Knowledge is the antidote to fear.

- Ralph Waldo Emerson

Introduction

Birds are grouped into a class called Aves.

Because they have unique adaptations for flight.

It is believed that birds first evolved from the archosaur of reptiles.

Birds have the following things in common with reptiles: one occipital condyle, one ear ossicle, the lower jaw structure, nucleated red blood cells, nesting behavior, and parental care.

Introduction

Birds however have some things that are unique to them:

Feathers, wings, endothermy, modified vertebral column, light bones, horny bill without teeth.

Fossil Records

Evidence from Archaeopteryx Shows that these ancient reptiles may

have climbed up trees with claws and then glided a flew short distances.

Another idea is that birds ran or hopped along the ground and then trapped prey with their wings.

There have been fossils found to show flight and some that show flightless birds.

Ancient Birds

Fossil Remains

Today

In the bird group there are about 9,100 different species, divided into 27 orders.

See page 329, the table will be on the test

Characteristics

Feathers- also called plumage Function to: allow flight, help species

recognize one another, mate attraction, endothermy, and waterproofing.

Color of Feathers May be due to pigments, reflected light, or

iridescence. Feathers are keratinized Contour feathers cover the body, wings,

and tail.

Contour Feathers

Structure of Contour Feathers 1. Consist of a vane with its inner and

outer webs, and a supportive shaft. 2. Feather barbs branch off the shaft. 3. Barbules branch off the barbs. 4. Barbules of adjacent barbs overlap one

another. The ends lock with the hook like hamuli (see picture on next slide).

5. The interlocking of barbs keep contour feathers firm and smooth.

Hamuli- Hook

Parts of the Feather

Contour feathers give the bird its characteristic

smooth round shape. They also give the bird its visual coloring and provide a first level of

defense against physical objects, sunlight, wind and rain. They are very

important.

Down feathers are smaller and lack the barbules and their

accompanying hooklets so they are not zipped

together and do not look as neat. In fact they are soft and fluffy.

They provide most of the insulation and are so good at this that

mankind for many years collected down feathers from various birds to put into sleeping bags and jackets to help keep

us warm.

Semiplumes are half-way between a contour feather and a down feather. These occur between the contour feathers and help to supply insulation and a certain amount of form

as well.

Filoplumes are very small and have only a very few barbs at their tips.  They are believed to have a sensory function, helping birds keep their feathers in order.

Diversity of Feathers

Feather Maintenance

Birds clean their feathers by preening (rubbing the bill over the feathers, keeps the feathers smooth, clean and in place.

Secretions from the oil gland at the base of the tail are spread all over the body which help keep the plumage water repellent and supple. This keeps the bill and legs from chafing.

Anting- many songbirds pick up ants with their bill and rub them all over the feathers. The formic acid that ants secrete is toxic to feather mites. So birds use them to keep parasites away.

An Egret Preening

Color of Feathers

Feather pigments are deposited during feather formation most colors in a bird’s plumage.

Other colors arise from irregularities on the surface of the feather that diffract white light.

An example of iridescence is the perception of interchanging colors on the neck and back of hummingbirds.

Iridescent feathers change color when seen from different angles or in different light conditions. The tips of the feathers have tiny platelets that either allow light to pass through or reflect it. The result is an amazing light show that has the viewer seeing a lustrous rainbow of colors. The peacock is the most famous of birds with iridescent feathers, but many of the more drab colored birds also display iridescence. The black parts of magpies and starlings sometimes appears

to be blue or green.

Molting

Molting- the periodic shedding of feathers The timing of molt periods varies. Flight feather are frequently lost in a

particular sequence so that birds are not wholly deprived of flight during molt periods.

However some birds like ducks can not fly during molt periods and have to hide in thick march grass until the molt is completed.

Duck Molting- this takes a couple of weeks

Other birds molting

Birds Skeleton

Characteristics: Lightweight, large bones have air

spaces, other bones are smaller in size. Like reptiles they have uncinate

processes, that strengthen the rib cage. The rear of the bird is adapted for

running, hopping, or perching. The neck is flexible The synsacrum and pygostyle support

and steady the pelvic region while walking, hopping, and flying.

Elephant Bird Skeleton

Skeleton Drawing

Key to worksheet

1) Skull  2) Cervical Vertebrae  3) Humerus  4) Second digit  5) Metacarpals  6) Fourth digit  7) Third Digit  8) Radius  9) Ulna  10) Scapula  11) Synsacrum  12) Pygostyle 

13) Ischium  14) Ilium  15) Pubis 16) Pelvic girdle  17) Uncinate process  18) Femur  19) Halux  20) Digits  21) Tarsometatarsus  22) Tibiotarsus  23) Keeled sternum  24) Coracoid  25) Furcula (or

wishbone)

The bonesWhile maintaining strength, most of the bones are pneumatic, meaning they are hollow and filled with air spaces

connected to the respiratory system. Skull The bones of the skull are generally fused

providing protection to the brain while being of light weight. A light, toothless beak replaces the bony, heavy toothed jaw of reptiles. Beaks, of course, can be highly modified for different types of food and feeding behavior   Note the large orbits, as sight is an important sensory mechanism for birds.

Neck

The necks of birds are very important for body maintenance and eyesight. Modification for flight has rendered avian forelimbs almost useless for any task other than flight. To make up for this lack of forelimb dexterity, the beak is used for many tasks such as preening feathers. To access hard-to-reach feathers on the back and tail birds require a flexible neck. Furthermore, as birds have immobile eyes, head movement and flexibility is required to focus on objects at various distances.

Thorax and Sternum

Overlying flaps projecting off the ribs called uncinate processes help to stiffen the rib cage so it will not collapse during the powerful strokes required for flight. The sternum is the highly modified breastbone. In flying and swimming birds the keel is enlarged for flight muscle attachment. Flightless birds such as Ostriches have a sternum without a keel.

Pectoral Girdle

The pectoral girdle is made up of the sternum, clavicle, coracoid and scapula. The clavicles come together to form the furcula, or "wishbone". The furcula provides a flexible attachment site for the breast muscles and along with the coracoids act as struts that resist pressure created by the wing stroke during flight. Flight muscles running from the sternum to the relatively short and stiff humerus elevate and depress the wing.

Pelvic Girdle

There is an extensive fusion of bones of the pelvic region to provide stiff support for the legs in order to deal with the stress of take-off and landing. The synsacrum is a fusion of the pelvic and 6 caudal (tail) vertebrae. At the end of the spinal column is the pygostyle, a fusion of the final few caudal vertebrae. The pygostyle supports the tail feathers and musculature.

Wing

The avian wing contains the usual arm bones of reptiles and mammals, but in a highly modified form. The humerus is rather short compared to the total length of the wing, as it must withstand the pulling of the flight muscles.  The radius and ulna form the support for the mid-wing. The outer wing or "hand" bones are highly fused for strength and feather support. The first digit or pollex supports the alula, a small feather used to control air flow around the wing.

Leg and Foot

The upper leg is composed of a fairly standard femur, but the lower leg and foot are highly modified by fusion of bones.  Of course, between the femur and the fibula and tibiotarsus is the knee, whose location in birds is often confused. The tarsometatarsus is an extended fusion of the foot bones. This lengthening adds extra leverage for running, landing and take-off.

Foot Types

SONG BIRDS or PERCHING BIRDS (warblers, thrushes, wrens, etc.) have independent, flexible toes, with one pointing backwards, ideal for grasping perches. Why don't perching birds fall out of trees when they sleep? When perching birds sit, a tendon on the backside of the ankle automatically flexes locking their toes around the branch. With feet locked, sleeping birds don't

fall. As the bird stands up its feet release.

WOODPECKERS have two toes pointing forwards and two backwards; for climbing up, down, and sideways on

tree trunks.

WATER BIRDS such as ducks have webbing between their toes for swimming.  GULLS also have feet

similar to these so they don't sink while walking in the soft sand or

mud near the water's edge.

WADING BIRDS. The long toes of herons, which spreads the bird's weight over a large surface area,

facilitates walking on soft surfaces near the water's edge

(where wading birds like to eat).

RAPTORS such as hawks, eagles, and owls use large claws (called

talons) to capture, kill, and carry

prey with their feet.

Pheasants and chickens use their strong feet to scratch the dirt and leaf litter to uncover seeds and insects.

Strong-legged flightless birds, like the Cassowary, protect themselves by kicking

with their powerful feet and sharp claws.

Skeleton Continued

Bird flight alternates between gliding and flapping flight.

It requires a lot of energy also called ATP.

The keel on the sternum is enlarged for the attachment of the strong pectoral flight muscles.

Airfoil design allows or creates lift.

Types of Nests Ground nests were probably the

first nests made by birds.  They are usually just "scrapes' on the ground forming a depression.  Birds shape these type of nests by rotating their abdomen in the same place many times.  Shorebirds typically employ this type of nest.  The picture to the left is a ground nest of a Killdeer.  An interesting note about shorebirds is that they almost always lay four eggs.

Types of Nests

Platform nests were probably the first elevated nests. Platforms eliminate risk from most ground predators.  These type of  nests, built by herons, cormorants, eagles and osprey (right) are very simple in structure.  Essentially they are a collection of loosely gathered sticks and twigs with a slight depression to hold the eggs.  Platforms can get quite large because some birds use the same platform year after year adding more material to the existing nest each year.

Types of Nests Insulated cavity-nests shelter eggs

from cooling winds and allow the parent's body heat to warm the eggs more efficiently. Many species use cavities as their nesting location, including woodpeckers, titmice, chickadees, owls, and bluebirds just to name a few. Nest cavities also serve as a valuable roosting spot, giving birds a place to "hide-out" during inclement weather. Cavity-nesting species have a keystone role in the environment because many other types of animals use old cavities for their homes. For example, southern flying squirrels often use old red-cockaded woodpecker cavities for their nesting location.

Types of Nests

Cupped nests are the most recognizable, most solid, and most complex of all of the nest types. Most songbirds build cupped nests in a variety of shapes and sizes. The pictures below illustrate several types of cupped nests and the species that build them. 

Digestion Birds depend heavily on their digestive

systems to remain nourished and healthy.  Many birds can starve in hours if deprived

of food, therefore, their digestive system is faster and more efficient than those of other vertebrate groups.  

Digestion in birds involves a lot of organs, each performing a specific function. It begins with entry of food via the beak and ends with waste exiting at the vent. Food is broken down and absorbed for use along the way.

Digestion

The discussion of avian digestion begins with the mouth.

 1. Bird beaks or bills replace the lips and teeth of mammals and vary in shape, size, length and function according to the type of diet consumed. Seed-crackers such as finches have a short conical beak, while birds of prey such as hawks have a powerful hooked beak for tearing flesh  

Digestion 2. The tongue of birds, just as the

beak, is adapted to the type of food the bird consumes.

Woodpeckers have a long narrow tongue which functions as a spear, allowing them to extract insects from holes they drill in dead wood. 

Birds of prey and finches have short, thick, fleshy tongues which allow them to manipulate their food.

Fowl and pelicans have tongues which allow the food to be easily shoved to the back of the mouth for swallowing.

A birds mouth is relatively unimportant in eating and digesting food in comparison with, for example, the mammalian mouth.  However, most birds do have salivary glands and the beak and tongue do help birds manipulate food for swallowing.

Digestion

3. After leaving the mouth, food passes through the esophagus on its way to the stomach (in birds called the proventriculus).   Many species of birds have an enlarged area of the esophagus known as a crop. The crop is well developed in most species and serves as a temporary storage location for food.

4. Crop shapes from various species of birds

The crop also allows food to be softened before it enters the stomach.

Pigeons and doves produce "crop milk" that they feed to their young for the first two weeks after hatching. Other species, such as ospreys, will regurgitate food that has been stored and softened in their crops and feed it to their young.

Digestion

5. Birds have a two part stomach, a glandular portion known as the proventriculus and a muscular portion known as the gizzard. Hydrochloric acid, mucus and a digestive enzyme, pepsin, are secreted by specialized cells in the proventriculus and starts the process of breaking down the structure of the food material.

The food then passes to the second part of the stomach, the gizzard.  The gizzard performs the same function as mammalian teeth, grinding and disassembling the food, making it easier for the digestive enzymes to break down the food. In most birds the gizzard contains sand grains or small rocks to aid the grinding process.

6. The small intestine is where food is digested and absorbed.  The small intestine varies in length and structure depending on the diet of the species.  Carnivorous birds tend to have shorter, less complex small intestines.  Herbivorous birds have longer, more developed small intestines.  Enzymes, produced in the pancreas, break down proteins and fats in the small intestine.  Nutrients are then absorbed through the intestinal membranes and into the bloodstream. 

7. The avian large intestine is reduced to a short, featureless connection between the small intestine and the cloaca. 

8. The cloaca is the final holding area for the waste products of digestion until they are voided through the

9. vent

Bird Beaks

Did you ever wonder why there are so many types of bird beaks or bills?

The most important function of a bird bill is feeding, and it is shaped according to what a bird eats. The bill is one of the characteristics used to identify birds.

You can learn about bird behavior by looking at the bill and thinking about what it eats. Then you may think about where it lives, and so on. Following are some common bill shapes and a description of the food they are especially adapted to eat.

Cone Shaped Bill

A cone shaped bill is found in many birds such as finches and grosbeaks. It is a strong beak used for cracking seeds.

Slender Pointed Beaks

Thin, slender, pointed beaks are found mainly in insect eaters. They are used to pick insects off leaves, twigs, and bark. This warbler is a good example. Woodpeckers have strong beaks which taper to the tip, forming a chisel for pecking holes in trees for food or nests. Most feed on insects which live under the bark.

Beaks

Hummingbirds have long, tubular bills that resemble straws, which they use to sip nectar from flowers

Mergansers, specialized for eating fish, have sharp tooth-like structures on the edge of the bill to hold fish tightly.

Hawks, owls, and other birds of prey which catch and kill live prey have sharp, "hooked" beaks. These are used to bite the skull or neck and also to tear the body into

pieces small enough to swallow.

The edges of a Mallard's bill are fringed to strain plants, seeds, and small animals from mud and water.

Beaks which are flat and wide at the base are found in birds which catch insects in flight, such as flycatchers. These birds also often have whiskers at the corners of the mouth, which effectively widens

the mouth opening, allowing more

effective capture of prey.

Respiration

Avian Respiration The avian respiratory system delivers

oxygen from the air to the tissues and also removes carbon dioxide.  The avian respiratory system is different from that of other vertebrates, with birds having relatively small lungs plus air sacs that play an important role in respiration (but are not directly involved in the exchange of gases). The air sacs permit a unidirectional flow of air through the lungs.

Unidirectional flow means that air moving through bird lungs is largely 'fresh' air and has a higher oxygen content. Therefore, in bird lungs, more oxygen is available to diffuse into the blood.  In contrast, air flow is "bi-directional" 䁩 n mammals, moving back and forth into and out of the lungs.  As a result, air coming into a mammal's  lungs is mixed with 'old' air (air that has been in the lungs for a while) and this 'mixed air' has less oxygen. 

Respiration

The air sacs can be divided into anterior sacs and posterior sacs. Air sacs have very thin walls with few blood vessels. So, they do not play a direct role in gas exchange. Rather, they act as a 'bellows' to ventilate the lungs. 

Respiration

So, how does air flow through the avian lungs and air sacs during respiration? 

1 - On first inhalation, air flows through the trachea & primarily into the posterior (rear) air sacs

2 - On first exhalation, air moves from the posterior air sacs & into the lungs

3 - With the second inhalation, air moves from the lungs & into the anterior (front) air sacs

4 - With the second exhalation, air moves from the anterior air sacs back into the trachea & out

It takes two respiratory cycles to move one "packet" of air completely through the avian respiratory system (see 1, 2, 3, and 4 above). The advantage is that air, high in oxygen content, always moves unidirectional through the lungs.

Respiration

Migration Migration is the seasonal movement of

animals from one habitat to another. Animals migrate between their wintering and breeding habitats. Some creatures that you would recognize that migrate are: whales, fish, butterflies, turtles, and of course birds. Some animals travel incredible distances on these annual journeys. The longest migration of any known animal is that of the Arctic Tern, which travels 15,000 miles from the North Pole to the South Pole and back again each year! 

Migration Migrating birds follow established

migratory routes. Migration in North America is essentially north-south along four major routes known as "flyways:" Pacific, Central, Mississippi and Atlantic.  Many birds migrate between North and South America and are referred to as Neo-tropical migrants (Neo = new + tropical).  Most of these birds migrate 500 miles non-stop over the Gulf of Mexico.  Other birds island hop down the eastern coast of the U.S. (see maps below).  Upon arrival in southern wintering grounds, birds have been described as nothing more than "feathered skeletons" having depleted much of their fat and muscle reserves. 

Migration

Why do birds Migrate? Seasonal cycles of climate or insect abundance attract

corresponding cycles of breeding, flocking, and migratory relocation.

Migration benefits are species or population specific and include the need to escape inhospitable climates, probable starvation, social dominance, shortage of nest/roost sites, or competition for food.

Another way to view the same ecological forces is that migrants aggressively exploit temporarily available opportunities.

Traveling to different habitats enables birds to find plenty of food throughout the year. For example, in the winter, when food sources are limited in northern areas, waterfowl such as geese fly south to areas that have mild weather and abundant food.

Bird on a Mission

Migration How do birds navigate over such large

tracts of land and ocean? It has been demonstrated that birds rely on

several different cues – visual landmarks, geomagnetic field, solar compass, skylight polarization pattern/stars, and olfaction - for their orientation and navigation across vast stretches of land.

Schlicte and Schmidt-Koenig (1971) fitted well-trained homing pigeons with frosted contact lenses that limited image formation beyond 3 meters. The blind birds flew over 170 km directly back to their lofts. Of course some crashed into the loft and some missed the loft altogether!

Migration Patterns

Migration

Brood Parasitism Birds are well known for their parental

care, patiently incubating their eggs and then bringing food to their young until they are old enough to look after themselves. However, certain birds, known as "brood parasites," lay their eggs in the nests of other birds and do not provide any parental care for their own offspring.  Care that the "hosts" provide to the young parasites is care denied to their own young.  This often has a detrimental effect on the reproductive success of the hosts and may affect their population numbers as well.

There are two types of brood parasitism, non-obligate and obligate.  Non-obligate brood parasites lay eggs in the nest of cospecifics (i.e. same species) and in their own nests.  Examples include several colonial nesting species such as Bank Swallows or African Weavers.

Obligate brood parasites lay eggs in nests of other species and have completely lost the ability to construct nests and incubate eggs.  Examples include Brown-headed Cowbirds and European Cuckoos.  About 1% of all known bird species are obligate brood parasites.  Other obligate brood parasites include: all African Honeyguides, about half of the species of cuckoos, the Black-headed Duck in South America, Shiny Cowbirds, Screaming Cowbirds, Bronzed Cowbirds, and Giant Cowbirds.

Brood Parasitism

Brood Parasitism

Brood Parasitism