Class Aves: Birds

The birds of the world are divided into several orders. We have listed the extant orders here according to current taxonomic information.

bird orders

Overview of the avian information here

This page is designed to be a rough overview of a standard introductory ornithology course. It covers the following: systematics, bird origins, feathers, flight, physiology, feeding behavior, senses, seasonality, migrations, optimal foraging theory, flocking, territoriality, mating systems, reproduction, growth, parental care, nestlings, breeding, geographic variation and population dynamics.


Birds are such a diverse assemblage that some order must be found among them so that we can better understand their relationships. Modern bird taxonomists have developed methods for looking at the relationships of birds. In the past, most of these methods were based on morphological features, whereas today a lot of work is being done on an examination of the molecular similarities between birds.

For modern birds there are a few prominent features that stick out that have been used to differentiate them from one another. The primary two are the palette and the ankle bones. The first big division in birds is in the Neornithes: a separation of the Neognathae and the Paleognathae

The Paleognathae are represented by large (mostly) flightless birds such as the Moa, Emu, Cassowary, and other ratites. These birds have a paleognathan palette, and premolars that are connected to the braincase.

The Neognathae represent the rest of the modern birds. Their palette is much smaller and their ankles have, instead of a process on the astragalus, it’s the calcaneum that has the process.


Why is it important to study the relationships of birds? Probably the best use of bird phylogeny or cladistics is to answer larger questions, such as those posed by biogeography. How might a group of birds have gotten from one continent to another? Why this distribution instead of others? If you look at one group, the Paleognathae, we can examine the possible uses.

The Ratites, are Paleognathan birds that are usually fairly large and flightless. The Cassowary of Australia and New Guinea is more closely related to the Emu of Australia than it is to the Ostrich. The Ostrich is fairly closely related to the Rheas of South America. We know now that Africa and South America were at one time connected. The study of these birds helped shed light on the dilemma of continental drift.

So how do you relate birds to one another? Cladistics is one common way. Cladistics uses shared, derived characters to determine the overall relatedness of each. For a detailed report on how cladistics are used see the Introduction to Cladistics

Biochemical Systematics

In addition to morphological traits there are a few different types of molecular or biochemical techniques used to show the relationships of birds.

  • Protein electrophoresis
  • Restriction-fragment-length polymorphisms. (RFLP’s): take restriction enzymes and cut the mitochondrial DNA’s into base-pair specific sets.
    o Take the mDNA and put a bunch of enzymes in it.
    o Then you run them through an electrophoresis.
    o The more similar the fragment lengths the better.
  • DNA hybridization
    o Two strands held together by chemical bonds.
    o Within the same molecule the bonding is very strong.
    o But if you split the DNA from one and mix it with those of another taxa.
    o If you heat them up you can measure the point in which they start to dissociate. The the higher the temperature needed, the closer related they are to each other.
  • Sequence Data:
    o Takes a chunk of DNA and sequences this.
    o It has a few approaches: One would be a few individuals with long sequences and another, many individuals with shorter sequences.
    o Apapane from Maui; or Apapane from Kaui.
    o In this sequence, there is only one difference from the two islands. WOW.
    o Yet, if you look at the apapane to amakihi’s they are more different.
    o Considered to be the most powerful way of doing systematics; also the most expensive.
    o Sequence long regions of less rapidly evolving sequences, with more rapidly evolving sequences.

Bird Phylogeny

The process of determining relatedness in birds is a very complex process. Part of the reason for this is that birds are very similar. If you take a horse and a dog, both of which are mammals, there are significant differences between their skeletal make-up. If however, you do the same thing with the skeleton of a chicken and a parrot, you won’t find those differences. The complexities of the skull, pelvis, pectoral girdle, and foot are almost entirely the same!

If you look at a chicken you see the same thing. You can learn avian systematics by looking at any part of the bird. You could take any two orders of bird and their skull would be nearly identical. A horse and dog would be very different, but not with birds. This is part of the reason systematics is so difficult. The body plan has very little morphological differences in them!

Origin and Evolution

Consider for a minute the diversity of birds. There are nearly 10,000 species! Is it possible to trace these birds back to one common ancestor? If so, who is it?

One of the major criticisms of Darwin’s Origin of Species was the apparent lack of any evidence showing the evolution of birds. Then, as luck might have it, only two years after he first published his book, Archaeopteryx appeared in a site in Germany.

Today there are 8 preserved fossils of Archaeopteryx in various museums of the world. What an amazing find for science because it stirred scientists to try to figure out how birds were related to other creatures.

Archaeopteryx was amazing for a few reasons. First it superficially resembled both a bird and a reptile. In fact, except for the feathers, the bird-like feet, and the fact that it had a wishbone (furcula) it didn’t really look like a bird. The jaws had teeth in them, of which no bird today has teeth. It also had the ankle bone fused to the shinbone. Clearly this bird had features of dinosaurs AND birds. So where did birds evolve?

Three hypothesis on origin of birds finally arose:

  1. Therapod dinosaur hypothesis: The first was a hypothesis that they came from the therapod dinosaurs. Therapods are meat eating dinosaurs such as Allosaurus.
  2. Crocodiles – the second hypothesis was that they came from crocodiles because they had an endolymphatic duct. Yet, as more research was conducted, they discovered that there was a tremendous amount of variation in this duct even among the lizards and other reptiles. Not many people today give much attention to this hypothesis
  3. Neither crocodiles or dinosaurs:Neither on the dinosaur line or the crocodile line. Reasoning because several dinosaurs were very specialized already.

Today we can show that birds are related in many ways to Dinosaurs. By using key characters we can use cladistics to understand better the relationships. For instance we can look at features they share in common with animals such as reptiles, and ancient dinosaurs in order to figure out where they may have evolved. They can thus, be linked generally to Ornithodira and more specifically to Manirapterans.

If you look at a cladogram of Diapsids which includes snakes, lizards, crocodiles (archosaurs), and dinosaurs and birds, you can get a better picture as to where birds fit in.

Dinosaur cladogram:
Looking in particular at the Ornithodira, Dinosaurs, Saurischian dinosaurs, Therapods, Tetanurae, Coelesaurs, Manirapterans. (list heirchial)

Ornithodira Advanced metatarsal ankle
Dinosauria 3+ sacral vertebrae; reduced fibula
Ornithischia 5+ sacral vertebrae, opptisthopubic pelvis, predentary bone in lower jaw
Sauropodomorpha 10+ sacral vertebrae, ankles have an ascending process
Theropoda Elongate, narrow metatarsus; hollow bones, metatarsal 5 reduced
Tetanurae (Allosaurus etc.), has a tooth row on the upper row that does not extend back past the orbital (eyes). Also has a antorbital fanestra.
Maniraptora because has a semi-opisthopedic pelvis. Means that the pubis bone of the pelvis is rotating backwards and has a foot.
Aviale Presence of feathers

Summarization of the set of derived characters that link them to the dinosaurs:
• Pelvis
• Clavicles
• Wrist

Once the idea that birds came from dinosaurs began, there was a scurry to find fossil evidence that could link birds back to their dino-roots. Several different dino-birds arose in the last century. One was Caudipteryx

In China a fossil was found that was dinosaur-like but had feathers. It seems that the wings would have been too small to allow it to fly, but, the fact that it had wings made it big news! Thus, the idea was that the initial evolution of feathers may not have been for powered flight. In fact, if you look at the tail feathers, it looks as though they are symmetrical around the shaft. This finding forced a reconfiguration of the systematics of the group.

Another fossil was found that, although it was not a fossil with wings, it was a closely related dinosaur to birds that was very small and appeared to be arboreal. This tiny fossil is only about 10 cm long and if it lived in the trees could have glided from tree to tree.


How did it evolve?
For almost a century scientists have been debating this issue. The common belief was that flight must have evolved from the trees down. This is because every known modern semi-airborn animal (glider), seems to be arboreal. Yet, another competing theory is that the wings are used to catch insects and thus evolved from the ground up.

One set of reasoning for the ‘ground-up‘ hypothesis is that dinosaurs could have been leaping to catch insects and wings allowed them to come down in one piece. Part of the evidence is that the capturing of prey was the same movement for flight.

Wing-Assisted Incline running. (copy of the study).
In a 2003 article in science, Kenneth Dial proposed his theory of ‘wing-assisted incline running’ as a way for wings to evolve. In the study he used chucker partridges and had them run up grades from 0 to 90 degrees. From 0 to 45 degrees, they just used their legs, but greater than 45 they used their wings too. When they flap their wings, they put traction on the surface and thus, increase their ability to run up the incline

Links about Bird Evolution and the Evolution of flight:

Feathers and Plumage

Have you ever seen a bird without feathers? Today, all birds have feathers and birds are the only animals with feathers. However, it would be inaccurate to use feathers as a way of defining birds. This is mostly because there were several non-bird dinosaurs that had wings. One of these was the Caudipteryx. This species had wings but they were not sufficient for flying. These extinct bird-relatives did use the feathers and plumage for many other adaptive things, such as insulation, breeding, and camouflage. We shall examine all of this and other adaptations for feathers and plumage in this section.

Types of feathers:

Bird feathers are amazingly complex. Each feather is made from the protein Keratin. While keratin also makes up snake and lizard scales, it is a slightly different compound in birds. The three main types of feathers are the filoplumes (sensory feathers), the contour feathers, and the down feathers (insulation).

One of the reasons bird feathers are so complex is that each feather is made up of many different parts. The feather is similar in many ways to a palm frond. The rachis (same as in palms) is the central core. The area that the feather attaches to the bird is called the calamus. The rachis has barbs that extend from it, which collectively make up the vane. If you’ve picked up a feather you’ll notice that at the bottom there are several ‘non-flat’ parts that are called the pennaceous section.

Along the feather, each barb has a shaft called a ramus. From each side of the ramus are barbules and barbicels. In essence they act like modern day velcro. One side can hook onto the other and keep the wing stiff. As a kid I’m sure everyone has run their fingers the wrong way down a bird feather and separated them. Birds can ‘zip-up’ their feathers by running them the other way and in essence, re-hooking the barbules and barbicels.

Down Feathers: These feathers do not have barbules on them even though they still have some of the same structure as a normal feather. They are normally very soft because they lack the stiff barbes.

Modified Feathers:

(OWLS) : Some birds have modified this arrangement. Owls for instance have velvet-like projections that extend from their feathers that allow them to fly silently.

(Sand-Grouse): Sand-Grouse that live in desert locations have feathers with highly curled barbs. These barbs will hold water when a bird dips into an oasis. This allows the bird to then fly back to the nestlings and they can drink from the birds breast.


There are 10 primary feathers, connected to the hands that are used to produce thrust (labeled with roman numerals) and several secondary feathers connected to the forelimb that are used to produce lift. There are also several rows of coverts on the upper and lower wing that are arranged in-between the primary and secondary feathers.

Look at a bird and you’ll notice that their wings are overlapping. Another type of ‘bird velcro’ is the connectivity of these feathers through friction barbules. They are also on the tail feathers (known as retrices).

Weird Feathers on Birds:

There are a few birds that have highly modified feathers. The following are some note able ones.

Nightjars: These birds produce a very elongated secondary flight feather that is used in breeding. It does not have aerodynamic properties and instead probably restricts their flight. After the mating season they fall off (or are bitten off).

Manikins: In the neo tropical forest, manikins form breeding leks and will often snap their feathers down, creating a very loud fire-cracker like sound. This is caused by the secondary feathers that have very large shafts.

Motmots: The tail-feathers of mot-mots are extremely elongated. These are probably used to give some sort of social signal to others of their kind.

Spatuletail Hummingbird: The Marvelous Spatuletail has a very long extended tail feather. Scientists do not know exactly what the purpose of this is. It is doubtful that there are any improvements in their flight because of it.

Honeyguides and Snipes: Their tail-feathers have a lot of space in between them. When air passes through it causes turbulence and a lot of noise.

Woodpeckers: The shafts of the tails of woodpeckers are modified for support so that when they perch on the side of trees they can brace themselves vertically.

Caprimulgiform birds (nightjars and kin): These birds have highly modified feathers that look like whiskers. They are actually just contour feathers, but are probably sensory adaptations to help them catch bugs.

Bristle-thighed curlews: These birds have modified feathers associated with the upper portion of their leg. These feathers are probably extra sensory feathers to determine the depth of water they are standing in.

Bird Feathers

How many feathers to birds have? To determine this you’d have to keep track of feathers into the thousands. When you plucked (as you would a chicken), you’d notice though that the feathers didn’t cover the bird like a grass covers your lawn. Instead there are rows (tracks) of feathers. Since the feathers overlap each other, its seems like they are all one continuous covering.

Preen Glands

Have you ever seen a bird nosing under its tail and then stroking its plumage? The preen gland, that hold the musty oils that help cover and waterproof the feathers are found just under the tail.

Bird Ecoto-parasites:

Feather parasites like lice, can really do a number of the feathers. They actually eat the feathers and effect the insulation of the birds.


Ever noticed that birds don’t stay the same color? Unlike humans, they can change color through a process of changing out the feathers. New feathers start to grow through the stalk of the old ones and are then ‘molted’. The basic coloration of a bird can usually be remembered as the ‘non-breeding’ color. The alternate coloration of the bird is usually the breeding plumage. Many birds will thus molt twice a year, once to the alternate and once to the basic phase.


The colors on bird feathers are caused by a combination of the pigments and the placement of the pigments on the wings. Certain pigments like carotenoids produce yellows, and reds. Others like melanins produce the browns and grays. Blue and green plumage is very different because they have many pigments that produce them.

The placement of the pigments are important because some birds have their pigments packed on the barbs and others have them on the shaft of the feather. Thus, if you were to examine a bird that had red on the barbs, a worn bird would appear less red!


Flight and Locomotion

Wing Basics:
Start out with an inclined plane (your hand). Hold it against the wind and experience the lifting force. First of all you get vertical lift and then drag. It has some of the properties of an airfoil. Are there better inclined planes than others? You can introduce camber to the plane. Camber is the curve. A streamlined airfoil is actually the most efficient. Lift is produced because the air flowing over an airfoil has a greater distance to go, thus producing a higher velocity, and a lower pressure on the top – resulting in a net lift.

Angle of Attack:
Another important aspect of lift is the angle of attack (defined as the angle the wing is to the oncoming air force). At a certain angle of attack the bird will stall and fall. This happens with planes if they try to fly up to fast- they stall. What is the critical angle of attack anyhow? This is a tricky questions because it depends a lot on airspeed. It also depends on the type of wing a bird has. For instance, certain birds that fly at low speeds, like vultures, have different types of wings with slits in them that allow them to break up turbulence and gain lift. (Birds also have an alula, or a mid wing slot that allows them to fly at different speeds – similar to the flaps on an airplane wing).

Adaptive Evolution in the Avian Wing:
(Evolution. 11 212–224) As early as 1957, Savile, an engineer, was able to examine the wings of birds to determine how the aerodynamics of the wings work. In particular, how does air flow over the wing? For any plane, air flows over the edges, causing turbulence that prevents lift. Birds have been able to reduce the turbulent airflow at the corners of their wings because they have wing-tip slots. Some birds have U-shaped slots, some have V-shaped, and some are square (square ones produce the most lift).

While lift is always an issue for birds, we have yet to talk about thrust, or the act of moving the bird forward. Just flapping a wing up and down isn’t going to move it forward, just up. For birds, their solution comes from the unique rotation of their wings. As the wings beat, the primary flight feathers actually twist to provide thrust. This twist is partly a result of asymmetrical veining of the feathers.

Types of Wings

  • High Aspect Ratio Wing:
    a. Much longer than it is wide. Has lot of vertical lifting area. Not much slotting.
    b. Not fast flying birds but more soaring birds
    c. Albatross, or Frigate bird.
  • Elliptical Wing:
    a. Tends to be even pressure over most of the surface.
    b. Usually found in birds that live in forests. … facilitates a subtle change in the angle of the wing.
    c. Sparrows.
  • High speed Wing:
    a. Falcons, Plovers
    b. Wings that are narrow and come out to a sharp tip. These wings reduce drag. More of the wing-beat is producing forward thrust.
  • High lift Wing
    a. Extreme slotting in the wing-tips
    b. Vultures, Eagles, etc.

Bones of a bird:
• Keeled sternum is very important in flight.
• Membranous portion around the wishbone (pectoralis muscle): Fits on the craco-clavicular membrane, depresses the wing.
• Muscles that raise the wing are found below, attached to the keel and the sternum- supracoracoideus. Originates on the keel of the sternum. Has a tendon that passes through a hole in the coracoid and attaches to the humorous.
• Classic study showed that the muscle of the supracoracoideus is raised solely by raising the wings. In the 1930’s, scientists cut the tendons on this muscle on crows and threw them out the window. Turns out they flew well but they couldn’t take off again.
• The dorsal elevators are used for fine movements in the raising of the wings. The crows mentioned above must have used these muscles to some extent.

Wing-propelled divers:
• Marvelous convergent evolution in these divers
• Great auks and penguins use their beaks for flight only.
• Also the plotopterid … giant pelican

When one looks at bird flight, you can not overlook those birds that have lost their ability to fly. In many ways, an examination of flightlessbirds can help us answer some important evolutionary questions. Here is a list of some examples:
• Cormorants on the Galapagos.
• Parrot in New Zealand: Kaka po
• Dodo’s of Columbiformes
• Owls flightless
• From Hawaii in the sub-fossil record there were a lot of geese.
• Hawaii had the only known flightless ibis. (nowhere else are ibises flightless).
This is a result of:
… Lost the keeled sternum.
… Coracoid and scapula have an angle greater than 90 degrees
… In birds that fly this angle is less than 90 degrees.

• Found on many islands of the world and many of them are flightless.
• Maybe the rails that can’t fly are just big babies (Neoteny).
• Flightless rails have the characteristics of baby rails that will eventually fly.

Foot-propelled diving:
• Lots of foot-propelled divers
• Most extreme were Hesperornis. It is believed that they were clumsy on land. Feet very far back on the body.
• The femur can’t rotate downwards.
• It forms a hinge-like articulation
• Leg muscles of divers are much more incorporated into the body.
• Foot-propelled divers have a cnemial crest.
Grebes have toes with expanded surfaces lobes. Great adaptation for them.


  • Tibiotarsus and tarsometatarsus are about the same length.
  • If the two bones aren’t the same length it makes it difficult to sit down.
  • Center of gravity should be over the feet.
  • You can compare two different postures.

Graviportal vs Cursorial.
• Graviportal Bird (Moa) has the bones right on top of each other.
…. Not fast runners – convergent with that of elephants and large mammals.
…. Aepyornithidae (Aepyornis medius)
…. Dinornithidae birds.
• Cursorial Birds (Ostriches): important for running. Their legs are built for running.
…. Struthionidae
…. Dromiceidae
…. Cursorial means moving on land.

• Running birds have reduced numbers of toes. Convergent with mammals.
• Typical Avian birds typically have 3 toes forward.
• Perching feet have two toes forward and one toe back.

Wadding birds
• Typical feet with big toes.
• Large toes provide greater surface area.
• Integrates locomotion with feeding.
Other toe adaptations
• Feathered toes increases the surface area by feathers on their feet.
• Lark and Jacana (Larks walk on sand and the Jacanas walk on lily pads).
Passerine Birds
• Under what circumstances do Mynas walk, hop and run?
• If they try to sit they stretch the tendons in their foot. Thus as they sit their claws tighten on the perch.
• The sheath of the tendons have ridges and the shafts have bumps. Thus as they sit, the tendons grip and don’t let go.
Locomote by climbing.
• There is a difference in the feet of birds that “climb up” and those that “climb down”. Birds that climb up have a longer claw on the front toe. Birds that climb down have a longer claw on the back toe.


Environmental Physiology.

Birds have unique metabolic rates and have thus been used as model systems for the study of metabolism. In essence, they are creatures that are living life in the ‘fast lane’ – more on that later.

If you look at the average body temperature of vertebrates you’ll find that birds have the highest average body temperature of all. They’re significantly higher than mammals and are actually right on the cusp of protein denaturation. As mammals we can increase our body temperature when we have a cold. Birds can’t do that. To understand why we must first understand a bird’s metabolism.

What is Metabolism? It is defined as the chemical activities that provide energy for power, endurance, repair, storage, and reproduction. It’s usually measured in kcal/kg/hr or as cc O2/g/hr. There are three types of metabolism that we measure in birds:

  1. Basal – metabolism performed when not digesting food.
  2. Existence – when an animal has to thermo-regulate or digest a meal. However, this metabolism occurs when it’s not locomoting or exerting any pressure besides standing on the ground.
  3. Productive – metabolism when an animal is walking, flying, or getting ready to produce sperm/egg.

Larger birds produce more energy per day than smaller birds. For instance, passerine bird metabolism is greater than non passerine birds for a given body size. Most passerine birds have a body temperature from 40-42 deg.

Birds have unique problems related to their flying habits. Here is a list of some of the main questions that are important to ask about bird metabolism.

  1. How is oxygen obtained in sufficient amounts?
  2. How is overheating prevented?
  3. How is heat loss prevented or heat conserved?
  4. How is sufficient food obtained and processed?
  5. How is water and electrolyte balance maintained?

cartoon bird lungHow do birds breathe?
This is a great question to examine because they breath very differently from mammals. In fact, their lungs are only a small part of their breathing apparatus. They also contain air sacs that extend anteriorly and posteriorly from the lungs. These sacs can be so large that they extend into the large bones in the legs. If you were dissecting a bird you could cut a leg in half and blow up the bird via these sacs. More or less, birds are just large feathered balloons.

While mammals have a sort of ‘cul de sac’ type of lung (that is ‘in and out’), bird’s lungs are more like radiators where there is a one-way flow through the lung. Movement of air through the lungs is as follows: Glottis – trachea – syrinx – bronchus to each lung – mesobranchus, dorsobronchus, ventrobronchus, parabronchus.

bird lung

To move air through the lungs one needs to have two inhales and two exhales. It’s a very interesting system. The first part of the lungs is the parabronchi. Within the parabronchi tubes are the small air capillaries that have cross-current gas exchange and thus provide oxygen.

birds alaskaBirds have two sets of air sacs. One set has connections near the front of the lungs. The other set has connections to the back of the lungs. These are the anterior (cranial) air sacs, and the posterior (caudal) air sacs respectively.

On inhalation both sets of sacs expand at the same time. This causes a reduction in pressure and air enters the bird’s trachea to fill the sacs. Half of the air enters the posterior air sacs directly. The other half enters the lungs at their posterior end and passes through the lungs to fill
the anterior air sacs.

The posterior air sacs become filled with fresh air while the anterior sacs become filled with breathed air.

On exhalation both sets of sacs contract at the same time. Breathed air passes directly out of the anterior sacs and out via the trachea. Fresh air is blown from the posterior sacs into the posterior end of the lungs and then passes through the lungs and out via the trachea.

One inhale and one exhale constitute a complete cycle. Fresh air passes through the lungs, in the same direction, when inhaling and exhaling.

Note that there is a small residual volume of air left in the lungs after the exhalation. It would require a second cycle before this air was expelled from the bird. This is the genesis of the 2 cycle idea.

Its only ~10% of the total lung + air sacs volume and some of it may persist in the anterior sacs even after the next cycle.

To read more about bird respiration visit these sites.

Some birds actually have a coupling between flight and inhalation and exhalation. For instance, when the sternum is pushed up through through the flying motion, a bird can exhale. During the rest of a wing cycle when the sternum comes down a bird can inhale.

When compared to the breathing in mammals, birds actually take fewer breaths. They also have hemoglobin that can hold more oxygen than mammals (due partly to a higher surface area resulting from the smaller size of the molecules).

Circulatory system of birds.
To transport the blood around the body of a bird, the bird must have an efficient heart. In fact, bird hearts are almost twice the size of comparable mammals. This is just another example of how birds are extreme high-powered animals. Finally, if you look at migratory and higher latitude birds they have larger hearts than lower latitude birds.

Heat regulation: Birds actually have great ways of regulating the heat in and out of their bodies. Lets look at the three ways heat can be transferred:

  1. Conduction: Heat transferred between two bodies that are touching each other.
  2. Convection: Movement of gases between solids.
  3. Radiation: Releasing energy like a light-bulb. Net radiation from the sun to any body on earth is an example of radiation.

For birds, heat is regulated in a few different ways. When birds are cool they shiver or fluff their feathers (to hold in heat), and if they are hot they have to use evaporative cooling (birds such as desert vultures actually poop on their legs to use this phenomenon). Birds such as penguins have the ability to use counter-current circulation in their legs to keep up their core body temperature. Some birds, will crowd together to stay warm. On a large scale, birds in colder environments are usually larger than others of the same species in colder environments (Bergman’s Rule). At night birds will reduce their body temperature and go into a state of torpor to decrease energy expenditure.

Kidneysbird droppings
Ever been on a long camping trip and run out of water? You pee out a lot of it but you’re not supposed to drink it. Our urine requires water to dissolve in and thus reduces our water supply every time we pee. Birds are different. They actually produce uric acid as opposed to urea. Their pee is like a paste and it is usually white. The fecal mater is brown. Thus when you think a bird has ‘pooped’ on you, its probably more likely it peed on you (its the uric acid)! In fact this system is so well adapted that they can concentrate their excrement to over 3000 times that of their blood!

Salt glands:
Another harsh environmental factor that birds must contend with are those of the saltwater environment. Saltwater birds actually have salt glands located close to their eyes that allow them to excrete salt. Actual secretion occurs through what looks like tears, but in reality is a salty drop of water!

Feeding Adaptations

We’ve looked before at the skeletal make-up of birds and concluded that compared to its counterparts, there is relatively little diversity. Even though the skeletal features of these birds are almost the same, they do have quite unique bills evolved for diverse ways of feeding. In this section we’ll examine some of the many ways that birds obtain their food.

Getting food in the aquatic environment:
If you were to analyze the behavior of birds in the ocean, you’d notice they have very diverse ways of obtaining food. In a 1971 classic paper on Seabird Biology, several techniques were noted, including:

  • Aerial piracy
  • Aerial pursuit
  • Dipping
  • Skimming
  • Pattering (petrels) : flapping wings and kicking feet to stay above the water.
  • Hydroplaning (Petrels) : open their mouth, flap their wings and move through water.
  • Surface feeding.
  • Scavenging
  • Surface seizing
  • Pursuit plunging: See the prey and pursue it.
  • Deep plunging: Boobies and Gannets.
  • Surface plunging: See the bird and just try to make one shot. Pelicans.
  • Pursuit Diving feet:
  • Pursuit diving wings.

Unique Adaptations

Owls have unique modifications of their ears to detect prey. They also have asymmetric ears and the feathered face acts as a reflective dish to hear sound.
Besides their amazing hearing adaptations, they have large raptorian feet. They have claws to grip the prey. They can hold the prey tight to suffocate them and use their claws to pierce them.

While most avian predators have large feet, these birds of prey don’t. They get prey by knocking it out as they collide with it in the air at speeds up to 190 mph. They actually hit their prey with their feet. In fact, they are so good that they actually aim for and hit their prey in the head. They have a tomial ‘tooth’ used to disarticulate the cervical vertebrae.

Snail kite:
These raptors, are birds that do not feed on the same type of prey as most of the birds in this group. Instead they have modified beaks to get snails out of their shells.

Vulture head shapes:
In Africa, one can actually see four different species of vulture that feed on the same carrion. The question is, how do all these species co-exist in the same environment? Fish (1944) noted that there are different sizes and proportions of the beaks and skulls of these different catharid vultures. In fact there seems to be a consistent degree of difference between the different size classes. The most likely answer is that these vultures partition their food. On a kill, for example, only the largest, rarest vultures are actually able to break open the skin of the large mammals. Once they arrive on the scene, the other vultures can finally feed.

Beak of a filter feeder (Duck / Flamingos etc).
The lamellae of the duck on the side of the horny covering (culmen) of the upper mandible is specialized for filtering out food from the water. They get a mouthful of water and the tongue moves the water out. Flamingos are interesting because they are upside-down filter-feeders whose mouths have adapted to this upside-down lifestyle.

Caprimulgiform Palate
The palate of a caprimulgiform bird known as a potoo has enlarged palatines that protect the roof of the mouth against the impact of large insects caught in the air.

Ways of soil probing/gapping
Many birds attempt to get insects and worms from the soil. There are two methods to this: probing and gapping. Probing is where no hole exists and the prober sticks its bill into the ground and can open the bill underground just enough to obtain its prey. Gapping (common in Mynas) occurs when the birds stick their bills in the ground and open their bills in the ground to make a hole. This is exposing a prey by moving the soil away with its bill.

Woodpeckers are bizarre in that their hyoid apparatus curls around and connects to the skull. Its an amazing adaptation for sticking out the tongue (which is attached to the hyoid apparatus). Their tongues, which have a spiny tip for stabbing prey, aren’t much longer than any other birds, but this long hyoid apparatus, which is attached to the tongue, in essence gives them a really long reach.

Cranial Kinesis:
This is a process of flexing back the tip of the upper bill. The bill of a snipe, for example, can be opened near the tip. This occurs through a rotation of the quadrate whereby it moves the jugal bar forward. The basal two-thirds of the bill is rigid, hence the mandible is bent further.

Seed-eating birds:
Seed eating birds have modifications of the skull including the trabeculae, and nasofrontal hinge which allow them to exert lots of pressure on seeds but have a flexible hinge that protects the jaw joint. Some birds are very powerful. The hawfinch, for instance, can crush olive pits. The amazing strength in the upper and lower jaws of these organisms allows the birds to deal with hard pits and seeds by shearing forces.

Sunbirds are basically the Asian equivalent of the hummingbird. They have beaks that are optimal for collecting food from flowers. The length of the bill is important because of the way these birds take in nectar. They stick out their tongue a bit from the bill and the nectar is extracted through capillary action.

Hummingbirds have simple stomachs because of the simplicity of the food they eat. (Turns out that sugar water is not good for birds. Birds can’t assimilate sucrose because it inhibits the assimilation of other dietary requirements.)

Crops are part of the esophagus and are used as storage areas for food.
A number of birds have them. Birds consume food, store it in the crop and then regurgitate it to their offspring. Digestive juices in the saliva break down food in the crop. Fish eating birds don’t have much of a crop because they are more commonly used for the digestion of nuts and seeds.

There are many different types of stomachs in birds including those of fish eaters, nectar feeders, and insect eaters. Birds will have some sort of stomach specialization depending on their diet. Seed-eating birds have very powerful stomachs. It is said that turkeys can bend pennies in their stomachs! The avian stomach has a glandular portion known as the Proventriculus which is an avian novelty. It is the place where food is chemically digested. The gizzard or the muscular portion is located behind the proventriculus. Another part of the stomach is the CECUM. Its the place of bacterial digestion. Birds with the best cecums eat leafs or seeds (ie. material that their own digestive systems can’t handle).

Central Place Foraging:
Birds are great for studying the theory of central place foraging because they have a central nest and then go out and forage for food. In this theory, the question is: should parents forage differently close to the nest compared to far from the nest? The answer is YES! Far from the nest parents return with more prey. In essence, this is an aspect of Optimal Foraging Theory.

Nervous Systems: Olfaction, Optics, and Hearing

In this section we look at the complex nervous systems of birds. This topic deals with bird intellegence, memory, vision, and hearing.

To start off this topic, lets imagine a hypothetical experiment with a captive dove. The researchers prepare a small apparatus that will present food to the dove if a certain button is pushed. How easily do you hypothisize the bird will learn how to attain the food? Its a classic experiment. To answer this question and to understand bird brains we must learn a bit more about how well the nervous system of birds is wired.

Bird brains

Birds have a three part brain composed of a section for olfaction, optics, and hearing. The relative proportions of each of these sections vary with the ecology of the bird. For example, birds such as vultures and falcons, whom detect low levels of methane gas, have a large olfactory section to their brains.

The cerebrum of the brain is the front part of the brain. It contains the cerebral cortex. In birds, more so than most animals, there seems to be a lot more cerebral tissue.

The hyperstriatum of the brain is a region that is cladisticly new in birds. This section of the brain is associated with intellegence. Smarter birds have a larger hyperstriatum. As a comparison, intellegence in mammal brains is associated with the cerebral cortex.

Birds that sing have a ‘song control nuclei’ also called the song control region. This region of the brain integrates with the main parts of the brain and ultimately controls the muscles. Migratory birds whose breeding season corresponds with their vocal activity have developmental plasticity in this section of the brain. In other words the song control region grows in the breeding season and shrinks in the off season.

Female birds have song control centers just like male birds do. They can have the wiring, but in general it’s the atrophy in the song-control center that causes them not to sing.

Some birds, like parrots, have the ability to mimic human voices and give the impression of communication. One African gray parrot named Alex is reputed to be able to engage in conversations. While it may be just a form of repeating sounds on cue, the form of communication is fascinating. Alex is even used as a communication tutor for other African gray parrots.

Many birds have incredible memories. Nutcrackers, for instance, can catch 2,000 seeds in an area. They then feed on their stashed seeds in the winter. They nearly never make a mistake when it comes to remembering where they stored the seeds

The part of the brain that deals with memory is the hippocampus. The hippocampus is found in the cortex of the brain. Birds that have large spatial memory have a large hippocampus.

The medulla is a section of the brain that birds used primarly in hearing. Take owls as a case study. Dark hunting owls who rely on their keen hearing have about 47,000 neurons in the medulla. Light hunting owls who rely on sight only, have about 11,200 cells in the medulla.

Vision in Birds:
As a general rule, birds have incredable visual capabilities. One measure of vision is acuity. Acutiy is the abilty of a bird to resolve fine detail at a distance. Compared to humans, birds have 2.5 to 3 times our acuity at long distance.

Bird eyes are also relatively large. They are on average 15 percent the mass of the bird head. Human eyes are ony 2 percent. The eyes of birds are locate on the side of their heads. Because of their relative positions, head bobbing, a behavior commonly seen in birds, is used to help them with depth perception.

To protect the birds eyes they have a nictitating membrane. These membranes help keep the eyes moist. In many ways it works the same as our eyelids. However, it is important to realize that these membranes are the same as our eyelids. The apparatus is different even though the function is the same. In fact, we have a vestigial nictitating membrane in the side of the head.

Physiological differences in birds also include bony osicles that surround hte eye. These osicles are also found in dinosaurs.

Birds also differ from us in the way that they focus images through the lens of the eye. Instead of fucusing by changing the shape of the lens (as humans do), birds change both the shape of the lense and the shape of the cornea.

Pectin is present in the bird eye. There are about thirty theories that try to explain this. No one is exactly sure what pectin is for. Possibly it is an avian novelty. Avian retinas do not have blood vessels in them like mammalian eyes do. Yet, the pectin is highly vascularized.

Cones are the daylight receptors. In the human eye there are about 200,000 cone cells per square millimeter. Birds have between 400,000 and 1,000,000 cells per square millimeter.

The fovea is an area of the eye with a considerable density of cone cells. There are four types of cone cells: Near UV, green, yellow and red. Mammals only have three of these cone cell types. The spacing of the four different types of cone cells in birds are of equal distance. Over the top of the cone cells birds have three types of oil droplets (green / yellow / red).

As a general rule, birds have their eyes positioned on the side of their head. This means that at certain distances each eye will see a different image. Some birds can alter this typical patter though.

The yellow billed cuckoo can converge its eyes by moving them side to front. Bitterns have their eyes lower on their head to see bellow them. Binocular vision on in birds occurs when they have the eyes aimed forward. This gives them crossovers in images from both eyes. This cross-over allows them to deal with depth perception.

Most birds that have eyes on the side of the head have only one fovea. Fast flying biers have a temporal fovia. This temporal fovia allows them to see light from in front of them through each eye. This in turn helps with depth perception. Birds without this have to turn their head to get the same light in both eyes.

While birds can see much better than humans, they can often not hear as well. Part of the reason for this is that birds have less area of cochlea. Birds do have a tympanic membrane close to the surface of the ear. They also have a columella to the inner ear where the cochlea is. This bone puts movement into the fluids in the cochlea which is then detected by hairs in this region.

Hearing in owls:

• Barn owls for example
• Their eyes are at the same level, but the ears and plumage on both sides of the head are unique.
• Spatial asymmetry is very rare in nature. In fact the ear opens at two different heights of both sides of its head.
• Nucleus laminarus detects the differences of arrival of different neurons from the nucleus magnocellaris. Neurons on the same side as the magnocellaris of one side get to the laminarus at different speeds. Thus they can use their asymmetric openings, combined with a calculator in the medulla to get the distance.
Oil-birds can echo-locate in northern south America. They eat fruit.

• similar to hair-cells called herps cells.
• Basically the ending of a nerve surrounded by some cup
• As the cup moves (like with a feather), it detects pressure.
• Allows them to know where their feathers are etc.

Air velocity detectors
* Some seabirds are thought to have specialized air-stream pockets in their nasal passages.

Seasonality / periodicity


Birds can be seen as ultimate robots.


  1. Guarantee appropriate sequences in successive events of the temporal program.
    Ex. Morning and evening peaks of feeding activity.
  2. Anticipate future demands- readiness
    Ex. Body temperature, and activity, breeding seasons.

A book called the ‘Dictionary of Birds’ in 1985 has a figure where the chaffinch activity was documented.
* The idea is that you record the activity of a bird over 24 hours.
Endogenous: not learned: their rhythm drifts (its not normally 24 hours). Its in effect a ‘free-running’ rhythm. Its not quite a 24 hour period, a bit less.
– Zeitgeber: light regime causes the rhythm to occur again.
– Does it matter when the zeitgeber occurs to if it works?

Rhythm occurs because of the pineal gland. It is not the light sensor, like it is in reptiles. The pineal gland produces melatonin. Production of melatonin has a daily rhythm.

Red, orange and yellow light is effective at getting their testes larger (Benoit 1950).

Types of light regimes:

  • 12hours of light per day: 12:12
  • or 6:6:6:6
  • or 4:4:4:4:4
  • or 3:3:3:3:3:3

Males grew their testes best at a 3 to 3 rhythm.

Starling with different testes throughout the year:
When kept for 48 months at circ-annual rhythms it messed up throughout the year. Ie. Every day looks like the previous day.: Male starlings have certain times of the year that they grow their testes. This persists even if they don’t know what time of the day it is.

Old world warblers breed in central Europe and over winter in the Congo. Fly over the rock of Gibraltar and then turn left and fly to their destination in the Congo. When they return they fly strait north. Use an inc blotter on birds feet and try to find what direction birds are flying in. Birds kept in a cage in Germany orient themselves in the same direction as all the other wild birds. Direction of orientation is endogenous. Birds trapped in a cage in Germany when they should turn left, show unique directional preferences. Same with when birds should fly north. AFTER Gwinner and Wiltschko 1978, 1980).

We know a lot about orientation in birds, but we know nothing of navigation.

Migration / Navigation

Migration, as a topic, cuts across a lot of different disciplines. Birds pose a great group to study this phenomenon.

We can look at movements of any animal. By migration, we deal with seasonal movements. In other words, a bird is in different places at different times of the year. This is in contrast to sporadic movement. This kind of movement can be associated with the tracking of food sources. This is mostly on a local scale. If the birds, however, move to the same places every year to track food, this would be considered migration. Hummingbirds do this in Costa Rica where they move from high to low elevations. Another type of movement is considered dispersal. For example, breeding dispersal is when the young move away from the nest to utilize other areas. This is often called natal dispesal. BUT, when we talk about migration, we are only talking about seasonal dispersal.

Types of Movements
1. Seasonal
2. Sporadic
3. Dispersal

What drives Migration?
• On a basic level, the spinning of the earth drives migration. The earth is on a tilt so that the winter and summer have different amounts of light. Thus, at different times of the year there are differential amounts of productivity, depending on the time of the year.
• Birds will usually breed in areas that are high in productivity, and then leave that area in the off-season.
• Sunlight is a function of the earth’s tilt and location from the sun.

Examples (non-continental movements)
• Pennant-winged Nightjars breed in southern Africa during the rainy season, and then migrate across the Congo to its winter quarters in the Sudan in time to enjoy the insect-rich rainy season there. The Nacunda Nightjar in South America makes a corresponding migration between Venezuala and Argentina.

Examples (large migrations)
• Golden Plover – North to south America.

Unique migrators
• Bronzed Cuckoo – is from New Zealand that is a brood parasite that never sees its parents. It flies from N.Z. 1900 Km to Australia and then 1600 km to the Soloman Islands.
• Blackpoll Warblers – from New England to Venezuala non-stop.

Spectacular Homing feats
• Unusual sensory systems – birds use the earth’s magnetic field a lot. They also use the sun in a way that allows them to track the sun’s movement.
• Ingenious experiments: We have discovered some of the unique experiments where people have put birds on turn-tables and moved them around.

Proximate and Ultimate Factors
– Proximate: physiological or mechanistic in nature. HOW does it happen?
– Ultimate: factors shaped by nature’s selective pressures: Why does it happen?
– The problem with migration: If birds leave to avoid poor food resources, how can natural selection (which does not for-see the future) shape migratory behavior such that birds leave before food becomes scarce?).

Photoperiod (is invariant)
If birds focus on photoperiod early enough, they will be predicted to prevail in the population. Thus they are being shaped by selection.

Origins of Migration:
To look at the origin of migration we are going to have to look at the costs and advantages. It is of course, very energetically difficult to migrate. Thus, there must be some sort of pay-off for moving to another area for part of the year.

Another view of migration is that it’s simply taking advantage of breeding opportunities. Lots of tropical ornithologists state that many birds are tropical birds that just leave the tropics to breed. In fact, many studies have shown that these birds have territories in both the tropics and in their temperate regions.

If you look at migration, not all ages and sexes will actually migrate at the same time every year.
• The gain of arriving early is much greater for males than females. It’s also much more of a gain for young males than old males.

Changes in migration of birds:
1. Serin Finches: mediteranean birds that are non-migratory. Yet a population was established in northern Europe that became migratory.
2. Fieldfares – Found in Greenland where they are non-migratory versus in Europe where they are migratory.
3. Polymorphism in Robins: The Molting of migrants of the European Robin occur earlier than resident birds. The migrant birds also put on a lot of body mass at certain times of the year. The migrants also show a type of ‘migration restlessness’ called Zugunruhe.
4. Gulls innate nature: Gull Cross-fostering experiment. For birds, experiments have been done whereby the eggs of one bird can be switched with that of others. For example, Herring gulls are non-migratory, while Lesser Black-Backed gulls are migratory. People have switched these eggs around and looked for a change.

  1. Turns out that the young that were raised with the non-migratory birds, actually did migrate.
  2. The opposite, however, did move with the migratory parents because they thought they were just following the parents.

Black-caps and Micro-Evolution of New Routes:
• People noticed that Black-caps started spending the winters in Britan.
• Before the 1950’s a few would pass through Britan from Germany on their way to Spain.
• Banding birds has shown that these birds are coming from Germany. Thus, they were basically flying west to get to England.
• It’s amazing that this actually happens, and it wasn’t noticed until the 1950’s.
• So, researchers bred in captivity, males and females and got the F1 offspring. These offspring were then put into a cage to see which way they orient during the Zugenruhe. They showed that there is a heritable basis for orientation in blackcaps.
• In south-west Germany, the Blackcaps would, however, orient to the south-west.
• Thus, the point is that you can see micro-evolutionary change in a short period of time within 50 years.

Arrival times of different birds are almost entirely accurate. They are accurate enough that you can almost set your calendar to them leaving.

The Canada Goose will move to their breeding grounds with the movement of warmer weather, northward.

Predators can set their clock as to when to breed knowing when the food will be most abundant for the offspring.

Populations of different regions may overwinter in different spots.
a. the Fox-Sparrow shows this well.
a. In the Seattle area, there is no migration.
b. In the Pacific Northwest, migrates past the Seatle Population .
c. The ones up in Alaska, migrate down to Lower California.

The Golden Plover shows that the route from the breeding to the winter quarters are not always the same as the route from the winter to the summer breeding grounds.

Ancestral migration routes
• Pectoral Sand-Pipers: Many birds follow ancestral routes to winter quarters. The Pectoral sand-pipers for instance, has extended its range from Northern N. America have extended its range to Northern Siberia. But, instead of flying strait south they follow the ancestral breeding route, back into North America and then south to S. America.
• Arctic Warbler: Finland and Norway across Siberia to Alaska
o These birds generally migrate down to SE Asia.
o The birds are originally from Sibera. So the birds from Finland fly all the way to Siberia and then to SE Asia.
o They do this instead of flying south to the area that would be very close to their range.

Fourty-eight-hour records of the rate of activity of a first year male White-crowned sparrow, show that in April, the bird is inactive at night, but that in May there is much greater activity at night (this is when the bird migrates).

  • The amount of Zugenruhe increases with the distance that they have to fly.
  • Species that have different populations (migratory and non-migratory). The hybrids have intermediate amounts of Zugenruhe.
  • People have used radar to track bird migrations.
  • Black Gulls, fly way out over the Ocean to Bermuda before they fly south to South America. It’s believed they are tracking the winds.

How far to birds fly?
• Laysan Albatros can fly 510 kilometers a day.
• The Homing Pigeon can fly 1080 km a day.
• The Ruddy Turnstone can fly 1045 km a day.

Building fat for migrations
• Birds will get fat before they migrate.
• As a migratory species they can have 5 different levels of fat.
• Ruby throated hummingbird puts on 2/3’s of its body weight to fly across the Atlantic.
• Fat is used as a fuel for migration because it has a lot of calories per gram of weight. The metabolism of fat also uses a lot more water than the other forms of fuel (carbohydrates or protein).

Stop-Over Ecology
• Birds have evolved to fly to stop-over points in the middle of their migrations.
• People have studied just how far you can go depending on the amount of fat stored.

Arctic Tern:
• Flies 36,000 Kilometers a year!

Politics of Migration
• Stopover ecology. The quality of stopovers sites may be conservation hotspots.
• Migratory birds do not recognize national boundaries. Conservation applies both to breeding and non-breeding sites.

Orientation in Birds

Problems in Animal Movement: There are many challenges that birds have in navigation. A few of the main problems are listed here.
• The bird must know where it is
• It must know the direction of its goal
• It must be able to maintain a course in that direction
• It must know when to stop.
• Broad evidence in birds: philopatry in migration, homing experiments.

Homing Ability Hypothesis: There are three sets of homing ability hypothesis
• No external cues are used: idea is that its just random searching cues. Another idea is that there is some sort of inertial guidance (ie. They remember every twist and turn).This hypothesis also does not account for the first flight of young birds.
Single environmental Cue:
Visual Orientation : Birds can recognize certain landmarks, etc. Birds like seabirds seem to be lost until they find the ocean and then make a beeline for it.
o Magnetic – During solar flares, when the earth’s magnetic field is screwed up, causes confusion in birds.
Celestial (sun, stars) – Its been shown that birds have used stars to navigate their path. This also means that they must have some sort of internal clock
True Navigation

Expermients used to determing homing ability

  1. European Starling adults knew where they had to fly while the juveniles innately flew back to where they were supposed to.
  2. INK-Pad / Blotter wheel: The classic way migratory birds have been studied is to look at bird migratory orientation. Shows that the birds are oriented to different directions in the winter and summer (N and S).
  3. Altering the magnetic Field: Birds use the vertical component of the magnetic field in order to orient themselves to the magnetic field. 
  4. Magnets on a bird: Turns out that on an overcast day, the birds that have the brass on their necks could orient ok, but birds that have a magnet on their neck, they can not orient correctly. Another way that orientations can be messed up is to wrap coils of wire around the birds head. These electric coils (Helmholtz coils) will cause a magnetic field to occur and thus it shifts the birds orientation. If the magnetic field is reversed, they fly in the exact opposite direction.
  5. SUN Orientation: On a sunny day, most birds can orient correctly. But on an overcast day the birds in a cage have no preferred direction.
  6. If birds are using a magnetic compass they must be able to reset or calibrate their magnetic compass every few days.

Orentation or Navigation: We’ve learned that birds will orient themselves to where the sun is. However, how do you determine if the sun is used for navigation? This can be done with some sort of clock shifting. If you clock-shift them by 6 hours, this is basically 7,000 miles to the west. So, when you release birds by clock-shifting, the Navigation theory says that they should realize this and fly west.

  • Under the Sun compass hypothesis, you’d imagine that non clock-shifted birds are released they should all fly to their goal.
  • If you release clock-shifted birds, using the sun-compass hypothesis, then you predict that birds fly in a predicted wrong direction. This is exactly what happened.

Night Orientation: Using the Zugenruhe, birds with blotting paper can show predicted paths of orientation while manipulating it with a planetaria. By flipping the planetaria, they can flip the birds orientation. The birds, however, are not focusing on a particular star, but are focusing on the rotation of the night sky.

Optimal Foraging

Optimal Foraging Behavior:

Optimal foraging is strictly behavioral ecology. In this kind of analysis we look at the performance of a behavior. The assumption of the theory of optimal foraging is that organisms will be energy maximizers or time minimizers. Energy maximizers try to get the most energy out of an environment and time minimizers try to get the energy they need in the least possible time. Thus, any time energy is limiting, an approach such as this is very useful. Some examples of variations of this are:
• Optimal diet problem
• Optimal patch use problem
• Optimal load size problem.

Crows and Welks:
One example is the crows that drop welks on the ground to crack open the shells. The crow must make several decisions. Mostly, how high should it fly before it drops the welk? If it flies high, they need to drop the welk fewer times. But, the higher the crow flies, the more energy it spends. It would be possible to theoretically calculate which height is the most optimum to drop the welk based on the least energy expenditure. From this theoretical estimate you an go out in the wild and estimate what is the actual average height that a crow drops a welk. It turns out that the height seen in the wild is the same as the theoretical best value.

Handling time:
Another common optimal foraging experiment is to look at the optimal size of prey for a bird to get the most energy per time out of a system.

Central Place Foraging:
Birds are most known for this type of foraging theory. This is primarily because birds have a nest and will then go out to forage. The idea is that birds will bring back more or larger prey when they are away from the nest than when they are near the nest.

Marginal Value Theorem:
As a bird begins to eat in a patch, the food density decreases. What point should an individual leave a patch. How long will it take for an individual to leave a patch. If there is a patch that is close to another, the bird should leave sooner than if the patch is farther away. Thus, the use depends on the patch gain and the rate of travel between patches.


Sociobiology is defined as ‘the subset of behavioral ecology that specifically deals with social behavior.’

Types of groups that you can imagine include the following subsets:
1. Unrelated individuals (A school of fish for example).
2. Uniformly related individuals (not siblings). {For example, a group of cousins}
3. Variously close and distant relatives (perhaps with siblings) (ie. Mother, daughter, son, cousins, etc). This is probably the most common type
4. Siblings (with or without one or both parents)
5. Groups of genetically identical individuals.

Living in a group has several risks. Some of these include:
1. Increased intensity of competition for resources, including mates.
2. Increased likelihood of disease and parasite transmission.
3. Increased conspicuousness of predators or prey.
• Of these, you’ll always have 1 and 2 occuring, while 3 is not always the case.

Consider then the problems of the organisms in a group.
1. Subordinate male is rendered effectively strile by an aggressively dominant who keeps him away from ovulating females.
2. Dominate male who is cuckolded by a sneaky subordinate that he has not ostracized completely or killed.
3. Females unable to secure all the parental attention of the father of her children because of other females nearby
4. Colonial birds who must nest close to each other with maximum risk of having someone elses eggs deposited in their nests.

Selective background of group living.
1. Susceptibility to predation may be lowed because of aggressive group defense or because of oportuity for individuals to use the group as cover.
2. Nature of food resources may make splintering off unprofitable (large prey or patchy prey.).

Performance of a bird in a group: Shows that pidgeon’s reaction distance is increased with larger flocks. In other words, the larger the flock, the sooner they see the hawk. Thus, there is an advantage at least to wood pigeons when an attacking goshawk is nearby.

Predatory success while birds are in a group: (Kenward 1978) – The more birds there are in a group, the less successfull a hawk is. Some birds that form a ball when a predator is around. This in turn, may increase the risk of the predator because of the increased chance of getting hurt.

The idea that flocking reduces vigilance is a big deal: How important is predatation in the evolution of flocking? This can be done by comparing islands with mainland areas. Ed Willis came to Hawaii and compared them wrong. As it turns out, the birds do flock AND there are predators.

Part of the reason birds flock is because of vigilance behavior. A bird looking up can be considered more vigilant than a bird looking down. Thus, you can determine the amount of vigilance in a bird. You can also look at differences between males and females of dichromatic species. If you look at the vigilance rate, compared to the number of near-neighbors, you find that the vigilance rate goes down with increasing flock size. But the vigilance rates of single males are much higher than female birds.

Flocking: One aspect of flocking is interspecific flocks of birds. There are some flocks in Peru that have over a hundred species of birds. As it turns out there is lots of communication in the flock … including dis-communication.

Study in Hakalau: There were two different sites: Pedro and Pua Akala. In the less dense area, they would have to go way out of their way to find a flock. As it turns out, these flocks are full of insect-feeding birds. In general there are no differences in the flock sizes in the areas where the density is large, compared to areas where the density is lower. Pedro is the low density site. But, it shows that at the low density site of Pedro, that flocking is so important that the birds go out of there way especially to find these flocks.

Alternatives to the Benefits of Flocking:
• Social-Facilitation: the feeding rate, for example, may be increased when others are around. In other words, when others are around, there is an increase in fitness somehow.
• Local Enhancement: This concept deals with one individual that is successful at a particular location, attracting others to that location.
• Information Center: When individuals can learn from each other. For example, bank swallows hunt for insects. The idea is that the swallows are using each other to find the insects. If they nest too early, there are not many others to help find food. Another example is Ospreys feeding for fish. Schools of fish are also very patchy. Ospreys that nest near each other can look at other ospreys and see what type of fish and where their neighbor Osprey comes from. (For fish, such as flounder that are not schooling fish, a find does not attract other Ospreys to head out in the same direction.

Foraging in a Group:
• The probability of starvation plotted over the food requirement allows us to see that at different ‘food requirement conditions‘ there are better times to be a solitary, compared to a flocking bird.
• In a flock, not all organisms are equal. Is it better to be a dominant or a subordinant individual in a flock?
• The larger the flock size, the more aggressive confrontations there are in a flock.
• There are less scannings in larger groups, so the feeding curve also has an optimal level. In essence you can predict the optimal flock size.
• Flocking in birds has risk averse benefits. They reduce the varience in patches. In a risk prone environment they make take a chance and not forage with a group and end up dying.


When talking about Agonistic Behavior you can divide it up into Territoriality and Dominance:
1. Territoriality
a. Space related
b. Primary or exclusive use
c. Fixed area defended continuously for sometime.
2. Dominance
a. Aggressive encounter to reinforce status
b. Not necessarily space related.

If two birds were consistently displaying to each other along a seemingly invisible line, you would call that territoriality. If two males would go into the display wherever the met each other you would call it dominance.

For a territorial bird you can go to the same spot every day and find the birds. Thus, it is much harder to find and study a non-territorial bird.

Sanderlings can forage in flocks OR establish a territoriality. Phil Brunner has shown the same things for the Pacific Golden Plovers.

There is some difference in birds depending on the size of the territory being constrained by neighbors or by the energetics of moving around within it.

• Elastic Dickcissels theory: With the number of males increasing, the territory size decreases, down to some minimum number. If the size of the territory is too small it seems to loose any sort of value.

Types of Territories An all-purpose territory: if nesting and feeding is in the territory, and to some extent, sexual privacy.

  1. Nest site only territory: only within a short distance around the nest will the male drive off another male. Based on space.
  2. Leks: Aggregations of males to mate with females.
  3. Facultative territoriality: for instance, nectar feeders working to defend a spot.
  4. Blurred territories: some males may just defend the female’s space. The type of territory is not always cut and dry.

All birds of a home range (area that a bird uses), but only some of the birds have a territory. Most territories are a subset of the home range. All-purpose territories may equal the home range.

Tropical territorial species have territories year-round, while most temperate birds have territories only in the breeding season.

In a territorial system, there are a certain number of residents as well as a lot of floaters. Floats roam around looking for a territory but do not have one.

Manu national park in Peru (Amazing birding area)
• There are many different territories set up in the park.
• There are many species that share the exact same territorial boundries.

Brown was one of the first to put territoriality into a conceptual framework

  1. Territoriality
  2. Aggressiveness Economic defend ability.
  3. Competition

In the 1970s someone put out a hypothesis that got everyone riled up: The hypothesis was called the Super-territory Hypothesis. It was published in 1977. There must have been ten letters after this that said it was junk.
• Jerred Verner was the author of the super-territory. He basically said that you can look at birds and they are defending an area that is too large for what they need. He said that by looking at this, that by increasing the size of your territory you are decreasing the size of floaters. This would in-turn increase you relative fitness.
• Maybe when the birds set up the territory, they don’t know what its going to be like during the breeding time. In essence, unfavorable years may require a much larger territory.
• The concept of the Pubic Good was introduced. Anyone that would defend a smaller territory would reap the benefits of the others who were defending a larger territory. Thus it is not sustainable.

I’iwi’s in Hawaii show a classic example of facultative territoriality. When there is low-productivity, its not worth it to be territorial. When the productivity is really high, why be territorial because there is an over-abundance. It’s really at an intermediate level where it would be advantageous to be territorial. – conceptually its not worth it, but is this what happens in nature? Yes.

They would put a dummy in a feeder-box and vary the size of the stripe.
If the live great tit had a stripe bigger than the dummy, it would attack the dummy. If this is an honest signal, you can look at the stripe and know how to attack/defend it.
Shows that it doesn’t even have to be a living bird, but that the size of the badge is very important.

House Sparrow dominance
• There is a lot of variation in the badge on the sparrows chest. He found that the most dominant birds had larger patches.
• The important thing is that badge size really maters.

Variation in patches on Harrises Sparrows:
• With significant variation in the markings on a bird you are able to tell the difference between birds.
• This allows for individual recognition.
• More dominant individuals and older indivuals seem to have more dark plumage.
• SO, can you fake it!
• Dominant birds usually have a higher metabolism, higher hormone counts in their blood, and so it seems that it wouldn’t be possible to do this.
• But, you can color these individuals to see what happens.
• Turns out that most of the time they got attacked more often.

Mating Systems

Is there Romance left in nature, or is nature governed by so many instinctual selective devices that animals act more or less like machines run on a computer program?

The study of mating as a whole has been revolutionized in the last few decades. Let me start the discussion of mating systems in birds with a quick review of relevant terminology.

Monagamy (90 percent of birds): Birds have one mate.

Polygamy: mating system where an individual may associate with many different members of the other sex.

Polygyny: males pair with two or more females (2 percent).

Polyandry: Females pairing with several males. (1 percent) Found predominantly in shore-birds. Often occurs in sexual reversal (one sex is larger than another).

Polygynandry: Males pair with many females and females pair with several males. Basically a mixed mating system. It’s common if fishes but not with birds. Its characteristic of tinamous, and flightless ratites.

Promiscuity: Indiscriminate sexual relations (its doubtfull that they are indiscriminate, even though this is how it’s defined). Males though may be willing to copulate with as many males as possible.

Sexual Selection: Form of natural selection in which variation in fitness among individuals is generated by different mating success.

Sexual selection can arise from two different methods

  • 1) male rivalry: One male could deny access by other males to a female. For instance, territoriality would be a form of acquiring beneficial resources that would allow them better success in mating.
  • 2) Female preference: if females prefer some character of males, as a form of better fitness, they can greatly effect breeding traits.

Darwin’s notion of sexual selection

“Before we discuss further the question whether females select the more attractive males or accept the first whom they may encounter, it will be advisable briefly to consider the mental powers of birds. Their reason is generaly, and perhaps justly, ranked as low; yet some facts could be given leading to an opposite conclusion. Low powers of reasoning, however, are compatible, as we see with mankind, with strong affections, acute perception, and a taste for the beautifull and it is with these latter qualities that we are here concerned.”

Charles Darwin, 1871

The Descent of Man and Selection in Relation to Sex.

Wallaces response:

A young man, when courting, brushes or curls his hair, and has his moustache, beard or whiskers in perfect order, and no doubt his sweetheart admires them; ….

‘the permanence of female taste was ‘scarcely verifiable in human experience’

Goddes, P., and Thomson, J.A. 1889

The Evolution of Sex

When the concepts of sexual selection and mate preference were coming to the forefront on scientific thought, they were hotly contested. One of the main reasons for the debate was that the men in that day and age could not agree that human females had any preference for other males. If human females had no preference, how could birds have a preference?

Some of the evidence came from extra-pair copulations, also called extra-pair paternity.

Other evidence came from females of whom have a certain reperoire size that would choose males with a larger repertoire size (length of their call). Thus it is believed that the size of the song is a trait of male birds that has been shapped by female presence.

Its also important to show that males and sons have some sort of genetic linkage. One is that bright-stripped males were linked to bright-stripped sons.

Long tailed Widows in Africa: Males have very long tails. It’s a classic study to see if females prefer longer tails. Thus, he had several birds that were control. He also took some males and cut their tale, and took other males and glued their tales. Turns out that Female long-tailed widows greatly preferred males with longer tails.

Anders Molar did a study with Barn Swallows. He showed that female barn swallows preferred to breed with males that had long streamers.

Polygyny threshold model. (Orians 1969): Why would a female ever choose to be a secondary female in a males territory that already has a female, instead of being the only female in another males territory. You can basically look at fitness curves in relation to certain territories. There is a cost to being the secondary female would have a curve shifted down. Thus, how much better does a territory have to be to allow a female to choose to be a secondary female on that territory.

If ‘A’ is the decrease in fitness induced on a female by being the secondary female on a territory. ‘B’ is then the change in territory quality of two curves.

EPP: environmental potential for polygyny: A high potential for polygeny occurs if there is patchy distributions of resources so that one male can obtain more than his fair share of resources.

LEKS: Aggregations of males that come together for no other reason than to attract females. Its in leks that males can reaches extremes. The most dominant male will sometimes get more than 50 percent of matings.

European RUFFS: Some males in a lek look very different. For example the European Ruff an have a satellite male that looks almost albino. The terminal males are darker. The satellite males exist only to get the females that are inbetween male territories. (Photo by C.C. Doncaster).

Swallow-tail manikins: Engage in cooperative displays in leks. One group in a single lek can have a dominant male. There are three helpers in the group with the dominant. They will then engage in a marvelous leapfrog dance. The idea is that maybe the helper males are just younger males that need to learn the ropes from the older males. They are not closely related though. Or maybe the next helper may become the next dominant.

New Guinea Birds of Paradise exibit the extremes of gaudiness.

Cotingas of central and south America. In addition to colored feathers, birds have skin accessories. For instance, blood engourgment in the mouth area become erect when blood enters the area.

Reproductive Biology


The testes of a male bird increase significantly during the breeding season. This dramatic change seems to occur mostly in temperate and migratory birds. Its unclear if tropical birds really do the same thing or not.

The testes of birds are not much different than that of other vertebrate animals. The sperm are also very similar to other vertebrates. The acrosome is at the tip (for penetrating the egg). The midpeice, which is loaded with mitochondria is used for power. Passerine birds, however, do have a slightly different sperm morphology.

The cloacal protuberance is an extension from the abdominal body wall. This protuberance indicates a male. It’s the most common male external reproductive feature. The cloaca is where sperm, urine, feaces etc leaves the body.

For copulation, the male has to get his cloaca close to the tip of the cloaca of a female bird. The male protuberance is intermittent in the fact that it will change its length during the breeding season.

Roosters havea phallus or a penis. It is relatively short, in any case.

Ostrich males have a penis that’s about 20 centimeters long. Some birds of prey and galliform birds also have an intermittent organ that works the same as a penis.


Female birds also have an increase in the size of their reproductive organs. In birds, it’s generally the left ovary that is active. The ovaries look very similar to a bunch of grapes.

Each one of the circular ‘grape-like’ structures are called follicles that can be atretic or mature eggs. Inside each follicle is the ovum (germ cell), plus the yolk. An atrectic follicle is one that has started to develop but then aborted.

Growth and Development

Hatching is a momentous event because it is switching gas exchange from the surface of the egg, to now using its lungs. Birds have an egg tooth, which is a small point on its upper bill that is used to excavate a ring in the egg. The air space in the egg is used by the bird to drill a hole in the egg. The birds have a very powerful hatching muscle on the back of the neck.

Embryonated chick eggs: Eggs at hatching are usually about 18 days old (ish). Some people then use the eggs when they are 16 days old. Yet, there can often be communication between kids in the nest, and parents to the eggs. There are some calls that the kid in the egg can make to tell the parents what is going on. Thus, it seems to be that the young can feel when inside the egg!

There is a large change in morphology that occurs in the nestling period. The nestling period is from the time the first kid hatches to when the last kid fledges. Thus the nestling period leads to the fledging period. The act that goes from one to the other is the act of ‘fledging’. The fledging periods is from when the last kid fledges to when all the young are independent form the parents.

Altricial birds:
In these types of birds, the chicks are almost useless when they hatch. They are mostly featherless and their eyes are half closed. This is the form of full altricial. There are of course stages of altricial. Hummingbirds are extremely altricial.

Semialtricial kids are unique as well. These birds often have some down feathers, and large feet. Its also dependent on the parents but hatches at an advanced state.

A semi-precocial bird has its eyes wide-open and is covered in feathers.

Precocial chicks, are completely down-covered. It can walk. Its wings are not big enough to fly but it can walk. It can follow its parents around and its eyes and brains are well developed.

Superprecocial: mound builders
Precocial: duck, shorebirds, quails, grouse, murrlets
Altricial: songbirds, woodpeckers, parrots

Character Altricial Precocial
Eyes at hatching Closed Open
Down Absent or sparse Present
Mobility Immobile Mobile

Transition from incubating to taking care of the birds when they hatch.

Delivering food is an important aspect of parental care in altricial birds. The relationship between kids and adults must be very closely evolved when you have sharp bills (ie. Anhinga parent, and kids.

Most birds have a sigmoidal growth curve (s-shaped). The biggest difference between the different sized birds is not that they start growing faster, but that as the other stops growing, the other just keeps on growing more and more.

Endothermy is birds is unique. An altricial bird has no endothermy when it is born. It slowly gains endothermy as they begin to grow.

The growth curves vary significantly amount species. For example, a curve-billed thrasher has a slow growth curve. They fledge when they weigh less than their parents. Cliff swallows, however, actually grow very fast and looses weight after it leaves the parents. This is most certainly an insurance solution that makes sure that it doesn’t starve.

Tissue allocation hypothesis: Bob Brickleff:
If you take a leg tissue, you can grow it or mature it, but you can’t do both at the same time. Thus, tissue allocation, refers to a decision to increase mass or increase maturation of the tissue. Quails, which are precocial, put a lot into the maintenance of their leg muscles. Thus, the growth of the leg muscles is much longer. This is because for a given amount of growth there is a given amount of maturation. Other species like starlings, don’t really need to walk (its altricial), so it can add mass quickly and worry later about maturation.

The strategy of an altricial bird is to start with nothing and grow like mad! Te primitive state is the precocial state and the altricial state. Its believed that the altricial state has evolved to minimize the time for nest predators.

Some birds secrete food for their kids: pigeons produce crop milk. But flamingos and penguins also produce crop milk.

Parental Care

After eggs have been laid in the nest, the parents must incubate the eggs. There are several ways in which males and females can brood their young.

One change that forms in females is the brood patch. This is an area of the breast that gets thicker after having laid eggs. The tissues gets thicker and more wrinkled so that it increases the amount in contact with the eggs. It also gets highly vascularized. The incubation patch, thus, is quite literally a heating device.

Boobies incubate their eggs by not sitting, but standing on them. There are a few modifications that occur in the feet of these birds.

The incubation period of the birds is the time from the last egg to the time of first hatching. There a bunch of birds that begin incubating eggs, though, before they lay the last egg. Thus, there are some times when this definition does not always fit.

The Galliform birds (megapodes), manage incubation pits with rotting compost. They put sand over the eggs to prevent them from overheating. These birds are the ultimate in precocial birds (a young megapode hatches and has no parental care whatsoever. It hatches from the pit and is ready to go.).

The size of a brood patch can vary with the clutch size. For example, a number of galls, have clutch sizes of three eggs. Thus their brood patch has a nook for each egg.

Physiologists have spent a lot of time looking for the temperature of the eggs during incubation. One of the aspects of incubation is trying to keep the temperature of the egg fairly constant over the whole surface of the eggs.

Altricial species (who are born looking mostly like maggots) have a greater application of heat over time. Precocial species (which generate endothermy when they are still within the egg), do not increase their incubation over time.

The weight of the egg decreases over time from the time it is born to when it hatches. Usually there is about 14% loss over time.

Is incubation costly?:
To look at this you need to look at the metabolic rate of the individual. There is no evidence that incubation is more costly inside the nest than it is outside the nest.

Incubation constancy:
There is great variation between species in the number of times that a birds will stay on the eggs.

Sessions. Attentiveness:
When the air temperature is high, there is less heat loss from the eggs, so they spend longer off the eggs. As the air gets cooler, they spend more time on the eggs. Thus, incubation of the eggs is clearly ‘air-dependent’.

Incubation based on introduced species:
In a cold place the starlings, bring their ancestral patterns of incubation to it, but the crested myna in cold places does not do so well. Most of the reason for this may be because they have traditionally different incubation patterns. The crested myna in Vancouver simply doesn’t have the capacity to adapt at incubation.

Incubation periods of hole-nesting birds as compared to open nesting birds is slightly longer in hole nesting birds. Most notably because predation is lower in hole-nesting birds.

Classic study: Copper eggs
A dove was given metal eggs with an inlet into it to alter heat. When the egg is warm, the bird thermoregulates as if it is warm. When its cold, it’s the opposite. Thus the bird is treating the egg like it’s part of the core.

Other classic studies: Tinbergen looking at behaviorally how a bird recognizes its nest.

Nestling Behavior

Distraction displays:
One of the hardest things to do when looking for some nests is to follow the parents, because good parents lead you away from the nests. One example is faking an injury, etc.

Birds that nest of a cliff show huge amounts of aggression.

Classic studies:
Lars von Haartman (1949) was a Finish ecologist looked at the stimulus that parents used to give stimuli to the kids. Von Haartman then created an experimental nest box. He had a trapdoor in the bottom that allowed him to remove the bottom to see what the adult would do when it encountered young. So do the parents respond to hearing or to seeing.
You can start out with several young from several nest boxes, and make sure that everyone is very hungry. Now all the kids are very stressed. You can manipulate the young so that all kids are ALWAYS hungry. When you do this the parents increase their foraging behavior.

Reflection Pearls
The kids have a number of features that should be very attractive to the parents. There are markings on the pallet that are very bright. Thus, when they open their mouths, there is a lot of selection on the brightness of the mouth. They call these ‘reflection pearls’. Its been shown that parents prefer giving food to young with the most colorful mouths. The sides of the mouths are swollen in newborns. These edges of the mouth are very colorful. They are often filled with blood and red. If it is bright red it means that it doesn’t have much food in its stomach (food in the stomach takes blood away from this area). Brood parasites, will sometimes mimic the palatal markings of their host species.

Reproductive Biology


The testes of a male bird increase significantly during the breeding season. This dramatic change seems to occur mostly in temperate and migratory birds. Its unclear if tropical birds really do the same thing or not.

The testes of birds are not much different than that of other vertebrate animals. The sperm are also very similar to other vertebrates. The acrosome is at the tip (for penetrating the egg). The midpeice, which is loaded with mitochondria is used for power. Passerine birds, however, do have a slightly different sperm morphology.

The cloacal protuberance is an extension from the abdominal body wall. This protuberance indicates a male. It’s the most common male external reproductive feature. The cloaca is where sperm, urine, feaces etc leaves the body.

For copulation, the male has to get his cloaca close to the tip of the cloaca of a female bird. The male protuberance is intermittent in the fact that it will change its length during the breeding season.

Roosters havea phallus or a penis. It is relatively short, in any case.

Ostrich males have a penis that’s about 20 centimeters long. Some birds of prey and galliform birds also have an intermittent organ that works the same as a penis.


Female birds also have an increase in the size of their reproductive organs. In birds, it’s generally the left ovary that is active. The ovaries look very similar to a bunch of grapes.

Each one of the circular ‘grape-like’ structures are called follicles that can be atretic or mature eggs. Inside each follicle is the ovum (germ cell), plus the yolk. An atrectic follicle is one that has started to develop but then aborted.

Geographic Variation

Georgraphic Variation occurs in birds across the country and has been documented in several cases. Clinal factors for instance, have been found in even a single species. The Fox sparrow from California has a deeper bill than that from Idaho and Oregon. It is believed that this geographic variation and divergence is caused by local selective pressures such as by mate choice or rivalry.

When thinking about natural selection and adaptation it is important to remember that it works in two ways: 1) within a species (called intraspecific selection) and 2) on a newly formed species.

It is important to ask the question then: What generates this speciation and how does it persist (what maintains it)?

But, before we go too far into the discussion lets clarify some terms:

  • Hybrid zone – a zone of intergradation that can be stable.
  • Equilbrium model – hybrids are dead ends (sinks) that can not reproduce thus creating a sharp boundry between two pure populations
  • Bounded Superiority Model – hybrids are of equal or better adaption for habitat in an intergradation zone so as to out-compete the further encroachment onto the other’s range.
  • Clinal – gradients of character states, such as body size or feather color. The expression of the opposing actions of divergent selection and blending gene flow in contiguous populations can be dynamic or static.

Case 1: Hybridization and speciation
A study on blue-winged and golden-winged warblers represents a case of hybridization and the ecological aspects of speciation. The blue-winged warblers can live in a wider range of habitats and thus hybridizes with the golden-winged warblers. Thus ecological aspects will eventually decide the fate fo the golden-winged warblers.

Case 2: Yellow and black and Black morph Bananaquit
The Y&B morph dispersed to Grenada from other islands. Now it is replacing the B morph in a clinal fashion. There is a gradual increase in Yellow-black morphs. Is it a better competitor? Is this sexual selection? As it turns out females of the black morph actually prefer the yellow and black morph males.

The rest is straight from my notes

EX: Mascarine white-eye: Grey, Brown, Brn/Gry – very steep gradient across island

Generation of Geographical Variation
1. if heritable characteristics
2. non-heritable envt. Variation (House finch – food determines plumage color not genes)
3. Genetic drift on neutral or weakly selected characters
Genetic drift can overwhelm selection pressures if the latter is weak.

Heritability = ratio of variance attributed to sires and dams (G)/ envt. Variation + G

Heritibility of bill length = .35 to .36..plenty of additional variation in variance of bill length; raw material for nat sel. To act upon.
If no bill length changes there is stabilizing selection
RRBB eggs moved from the everglades to talahasee looked more like Talahasee birds and Oklahome birds to Minnessota looked more like Minessota birds but in both cases not totally showing that genetic component of heritability still influential.

-Amakihi nest morphology on big island
-Also young birds not re-captured as often as adults this shows substantial natal dispersal. Effective pop.size decreases with the decrease in natal dispersal distance. Small effective pop. sizes evolve faster and often in directions dictated by chance.
-Honeycreeper male plumage cline along Hawaiian Island chain evidence of clinal female sexual selection.
-latitudeinal gradient of clutch size N – greater S less,
– porosity of egg shells with altitude
– repertoire size .. W marsh wren and E marsh wren. The former has a larger song repertoire and this seems to keep the species from hybridizing – no intermediate forms have been detected however the W males may attract more E females and be slowly moving eastward
– area of A and B different # of allozymes (neutral character – no selection) but non-neutral selection may be occurring.

Population structure:

Same suite of changes throughout the pop. Dispersal and gene flow “enetic glue”

Individuals on each end of the range on 2 different evolutionary trajectories………. If individuals disperse can upset that.

Individuals needs to make it from point A to point B but needs to reproduce.

Theory: one individual per generation makes it into other population that pop. will not loose an allele. Can look at dispersal as geographic variation.

22-4 Males did not move much, nestlings moved a lot.. females tended to disperse farther than males.

Amakihi – juveniles go somewhere else
Akepa Juv.- Are not going anywhere.. show great changes from one island to the next.. they have much less dispersal of the kids
Apapane- Nomadic
I’iwi – juvenile dispersal

Generation of geographical variation by natural selection operating on heritable characters

Quantitative genetics of
1. morphological traits
2. behaviorial traits
Measure heritable characteristics operated on by natural selection

Measure non-heritable characteristics ? caratenoids in plumage (house finch)

Genetic drift (operating on neutral characteristics.. one’s that do not give the bird an ecological advantage): chance events associated with
– traits begin to look different
– no envt. Variation
– no envt. Selection
– just chance events of whose surviving and who is not

If weak selection, genetic drift can overcome it

All evolutionary processes come into play with geographic variation

Downy woodpecker: latidutinal cline
Galapagos finch competition – Santa Cruise: interspecific competition
Daphne major: Intraspecific competition

Population structure is geographic structure is maintained by natural selection

Dispersal = genetics glue

One individual only needs to enter population to make a change
Dispersal is life history character that maintains or generates geog. Variance.

22-1 Snow geese
Assortative mating offspring preferentially mate with birds parents’ color

22-1 Allopatric speciation diagram

Isolation barriers
EX: Australian robins
Aracari in Amazon basin…. Vicariant event (glacial period) reduced the forest to patches resulting in Aracari’s being divided ? speciating and then brought back together during interglacial (now)? they can not interbreed.
Mannikins – rivers are isolating barriers
22-9 Divergence temporary in Yellow-rumped warbler/Myrtle warbler now being re-joined – barrier gone
22-10 Orioles (hybrid zone)
Two theorys in static hybrid zones (see previous page)

Population dynamics:

The populations of many birds will vary significantly from year to year.

Population limitation can be caused by a number of different things such as food, nest sites, competitors, predators, disease, or harsh weather. Two of these limiters determine a carrying capacity or ceiling. These are food and nest sites. The other factors can maintain the population below the carrying capacity.

Example: experiments have been conducted on cavity nesting birds whereby they have correlated the number of birds with the number of dead trees. (Raphael and White 1984). Under a certain threshold of dead trees the birds are limited by trees. After a certain level, other factors probably limit their density.

Another few things to consider in any population of birds are their niche requirements and their habitat selection. Certain birds will choose certain habitats. .

Population regulation deals with density-dependent and density-independent factors that prevent a population from exceeding carrying capacity.
• Density independent factor: unrelated to the number of individuals in the population.
• Density dependent factor: strength of regulating factor varies with the number of individuals.

Example: A study was done in Finland showing that temperature can regulate a population. When plotted on a graph the relationship between Great Tits (Parus major) breeding numbers and mean temperature of the preceding winters in an area of Finland can be seen.. In the winters 1969-1971. In the winters 1969-1971, extra food was provided. Filled symbols – pair numbers after winter of food provision, open symbols – pair numbers after other winters. From von Haartman 1973.

Changes in Ecological Factors as they effect Populations of birds.

Some examples:
• The more grass-seeds the more sparrows there are:
• More birds in the type of sediment (which is related to the prey).
• Dipper territories are larger in acidic stream conditions.

Nest-site limitation
• Examples
Brawn and Balda 1988: cavity nesting birds in Ponderosa Pine forest in Arizona. Shows that populations of birds can be nest-site limited but if they are in areas where there are lots of cavities, nest-sites are not limiting.
• Dunn 1977: Weasels, which each rodents, will eat bird nests. The more rodents, the less nests are destroyed because weasels have enough food to eat. Yet, the higher the density of nests, the greater percentage of nests that are destroyed.

Ectoparasitism and Disease: (Examples)

• Brown and Brown 1986: Cliff swallow study. The bugs per nest and bugs per nestling increased with colony size.

Ideal Free Distribution: This is very important in population dynamics. This model is the null model.

• Individuals have knowledge of all habitats
• Individuals are free to move between habitats and stay in one of preference.
• Loss of an individual from Habitat A increases the fitness of the rest of individuals in A.
• Gain of an individual in Habitat A decreases the fitness of the rest of individuals in habitat A.

Species listed under Aves