BIRDS

6 Characteristics of Birds Endothermic (warm blooded) Vertebrates (Hollow Bones!) 4 Chamber Heart All Have Feathers All Lay Eggs Have Scales on Feet and Legs

Class Aves – Birds Birds are found in most every habitat from forests to deserts, even in caves. Some birds dive in the ocean to 45 m to catch prey. Birds have visited both the North & South poles. The bee hummingbird of Cuba weighs 1.8 g and is one of the smallest vertebrate endotherms.

How do birds fly? The top has less “air pressure” and this produces an UPWARD force (This is called lift!)

Specializations for Flight Weight Reduction Hollow bones No teeth or heavy jaws Only one ovary No urinary bladder Hot air sacs Huge Flight Muscles Rigid Skeleton Fused Bones Uncinate Processes Wishbone Efficient Respiration High Body Temp Sophisticated Nervous System

Bird Skeleton

Form & Function – Skeleton All birds that can fly have a large, thin keel on their sternum that provides area for the large flight muscles to attach.

Bird Skeleton Air Sacs

A bird’s most obvious adaptations for flight are its wings and feathers. Feathers are the feature that set birds apart from other vertebrates.

Form & Function – Feathers Feathers are lightweight, yet tough, consisting of: A hollow quill emerges from the skin. This becomes the shaft which bears numerous barbs that form a flat, webbed surface, the vane. Each barb contains many barbules.

Form & Function – Feathers Contour feathers are vaned feathers that cover and streamline a bird’s body. Called flight feathers if they extend beyond the body. Down feathers are soft and have no hooks on barbules. Filoplume feathers are hair-like – function unknown. Powder-down feathers disintegrate as they grow, releasing powder that aids in waterproofing.

Form & Function – Feathers As a feather nears the end of its growth, keratin is deposited to make some of the structures hard. The protective sheath surrounding the new feather splits open, and the feather unfurls.

Form & Function – Feathers When fully grown, feathers are dead – like mammalian hair. Birds molt to replace worn out feathers. Usually feathers are discarded gradually to avoid bare spots. Flight feathers & tail feathers are lost in pairs to maintain balance. Many water birds lose all their primary feathers at once and are grounded during the molt.

Flight - Wings are Specialized for Particular Kinds of Flight Elliptical wings are good for maneuvering in forests. High speed wings are used by birds that feed during flight or that make long migrations. Dynamic soaring wings are used by oceanic birds that exploit the reliable sea winds. High lift wings are found in predators that carry heavy loads. Soaring over land with variable air currents.

Mammal Respiratory system is not as efficient as bird system Bird lung Uses air sacs to make air flow one-way through lung Fresh air Countercurrent exchange Mammal lung Dead end system so Air is stale

Respiratory System There is an extensive system of nine interconnecting air sacs that connect to the lungs. Air flows to the posterior air sacs, to the lung, then to the anterior air sacs and out.

Efficient Respiratory System Air moves from outside bird into posterior air sacs by trachea Air moves from posterior air sacs to lungs Air moves from lungs to anterior air sacs Air moves from anterior air sacs out body by trachea

Food & Feeding The beaks of birds are strongly adapted to specialized food habits.

Digestion At the end of the esophagus of many birds is the crop. Used for storage. The stomach has two compartments: The first secretes gastric juices. The second, the gizzard, is lined with keratinized plates that serve as millstones for grinding food. Birds swallow small stones to help this process.

Owls can’t digest the bones & fur or feathers of their prey. These materials are bundled together and ejected through the mouth. Owl pellets can be used to determine what the owls in a particular area have been eating.

Excretory System Some birds, including marine birds, have a salt gland to help rid the body of excess salts. Salt solution is excreted from the nostrils.

Circulatory System Birds have a four-chambered heart. Separate systemic and respiratory circulations. Fast heartbeat – faster in smaller birds. Red blood cells are nucleated and biconvex. Mammals are enucleated and biconcave.

Nervous System Birds have well developed cerebral hemispheres, cerebellum (important for coordinating movement & balance), and optic lobes.

Senses Birds usually have poor sense of smell & taste. Some, carnivores, waterfowl, flightless birds have well developed sense of smell & taste. Birds have the keenest eyesight in the animal kingdom and also very good hearing. A hawk can clearly see a crouching rabbit a mile away!

Reproductive System Male bird sperm is produced in two testes that lie beneath the kidneys Sperm passes through small tubes called Vasa defrentia into the males cloaca During mating the male presses his cloaca to the females and releases sperm Females single ovary releases eggs into a long, funnel-shaped oviduct where they are fertilized by sperm

Reproductive System Reproductive System Cont. Fertilized eggs move down the oviduct, where they receive protective covering and a shell Unfertilized egg consists of a nucleus, cytoplasm, and a yoke When fertilized, the embryo is suspended in albumen, the egg white The liquid medium is supported by ropelike strands of material called chalaza that are attached to the shell membrane Female has a shell gland that secretes a protective calcium carbonate shell to surround the egg

Male Reproductive System The system is very unique and different from that of humans. Sperm formation occurs more rapidly in birds as compared to mammals. It takes from one to four days for the sperm to travel from the testes to the end of the ductus. Sperm undergo maturation in the male reproductive tract.

Female Reproduction System This system is unique to birds, unlike any other animal. Just like many other female animals, the avian female begins life with two ovaries and oviducts. At hatching, the left ovary contains all of the egg cells it will ever have. These cells will continue to develop once the hen reaches an age when she is able to reproduce.

Incubation and Development A female bird usually lays eggs in the nest. One or both parents will incubate or warm the eggs by sitting on them. The cover them with a thick, featherless patch of skin on their abdomen called a brood patch. In penguins the male emperor heats the egg by placing it on his webbed feet and enfolding it with his warm abdomen.

Characteristics of Birds All birds also have hindlimbs adapted for walking, swimming, or perching. Foot structure in bird feet shows considerable variation. All have keratinized beaks. All lay shelled amniotic eggs.

Birds who do NOT fly! Penguins Ostriches Emus

Living Birds Flightlessness has evolved in many groups of birds. Penguins (use wings to swim through water). Many fossil forms including flightless owls, pigeons, parrots, cranes, ducks, & auks. Usually occurs on islands with few predators.

Smallest / Largest Hummingbird Ostrich

The Origin of Birds Birds probably descended from theropods – a group of small, carnivorous dinosaurs. By 147 million years ago, feathered theropods had evolved into birds.

Evolution of Flight As the reptile line leading to birds became endothermic, the ability to conserve heat (insulation) was selected for. Longer scales = better insulation, up to a point At this longer length, besides providing better insulation, the scales provided lift for gliding. Now both insulation and lift were selected for, and feathers, wings, etc. evolved.

Retained Dinosauran Features Egg-laying Feathers as modified scales (new evidence indicates Velociraptors may have had feathers) Air Sacs

The Origin of Birds Archaeopteryx The oldest bird known. Skull similar to modern birds but with thecodont teeth. Wings with feathers were present.

The Origin of Birds Much of the skeleton was that of a theropod dinosaur. Long bony tail Clawed fingers Abdominal ribs S-shaped, mobile neck This fossil demonstrated the connection between theropods & birds.

The Origin of Birds Archaeopteryx arose from the theropod lineage. Closely related to Dromaeosaurs. More shared derived characters. Many had feathers used for insulation and/or social display.