Birds

Birds

Birds copyright cmassengale Evolution and Classification Birds are Vertebrates of the Class Aves The evolution of warm-blooded, has enabled birds to survive in virtually every known environment copyright cmassengale Origin and Early Evolution

Evidence from fossils and from studies of comparative anatomy indicates that birds evolved from reptiles Their features and their fragile hollow bones do not preserve well. copyright cmassengale Archaeopteryx

The fossil genus Archaeopteryx link between reptiles and birds, these mammals possessed characters of both reptiles and birds. Like reptiles it had a large skull with teeth, bones that werent hollow, claws on its forelimbs, and a long tail. Its strong legs and rounded wings indicated that it glided rather than flew copyright cmassengale Archaeopteryx

In contrast, the presence of feathers and of a furculum, the fused collarbones commonly called the wishbone, suggest that Archaeopteryx was birdlike After Archaeopteryx the next bird fossil dates from about 90 million years ago, in the Cretaceous period. copyright cmassengale Hesperornis

Hesperornis, a large, flightless, driving bird, probably resembled the modern loon but had reptilian teeth. A smaller ternlike bird called Ichthyornis had large wings, indicating that it may have been a strong flier. The development of sustained flight may have been enabled birds to colonize new areas during the Cretaceous. copyright cmassengale

Classification Most taxonomist classify the nearly 9,000 species of Class Aves into 27 orders To classify birds into orders and families taxonomists most often use morphological evidence from beaks, feet, plumage, bone structure, and musculature. copyright cmassengale Characteristics of Birds

The following characteristics distinguish birds from other Vertebrates: Body covered with feathers Bones are thin and hollow The forelimb function on wings are used for flight not grasping The two hind limbs, with clawed toes support body A toothless, horny beak is present Body temperatures is generated and regulated internally The 4-chambered heart has a single right aortic arch

Amniote eggs are encased in hard, calcium-containing shells. Most species eggs are incubated in a nest. copyright cmassengale External Characteristics Soft, fluffy down feathers cover body of nestling birds and provide and insulating undercoat for adults. Contour feathers give adult birds their streamlined shaped and provide coloration and additional

insulation Flight feathers are specialized contour feathers on the wings and tails Hairlike Filoplumes, or pinfeathers, and dust filtering bristles near nostrils copyright cmassengale Feathers Continued Feathers develop from thin pits in the skin called follicles At maturity each vane has many branches called barbules that are equipped with microscopic hooks.

In the process called preen gland located at the base of the tail. The major molt, during which the birds replaces its flight feathers, occurs in the late summer between breeding and migration. copyright cmassengale Beaks and feet Hawks and eagles have powerful break and clawed talons that help them capture and then rip their prey. Swifts have a tiny beaks that opens wide like a catchers mitt to share insects in midair. The feet of flightless birds, on the other hand are modified for walking and running

copyright cmassengale Skeletons and Muscles Combine lightness and strength Bones are thin and hollow The fused bones of the trunk and hip vertebras and the pectoral and pelvic girdles Fused bones form a sturdy frame that anchors the powerful breast muscles

during flight and supports the muscles when a bird is walking or at rest. copyright cmassengale Skeleton The sternum supports the large breast muscles The humerus, ulna, and radius, along with the pectoral girdle and the sternum, support the wing. The pygostyle, the terminal vertebra of the spine, support the tail feathers, which also play an important role. copyright cmassengale Endothermy Generate and regulate body heat

internally Enables birds to inhabit both cold and hot climate Body temperature ranges from 4046 degrees Celsius. To help conserve body heat, birds fluff out there feathers to insulation. copyright cmassengale Digestive and Excretory system Food passes from the

mouth cavity straight to the esophagus. Enlargement of the esophagus called the crop stores and moistens food. In the first chamber, The proventriculus, gastric fluids begin breaking down the food. Then passes through the gizzard, a muscular organ that kneads and crushes the food copyright cmassengale Excretory System

The avion excretory system is also efficient and light weight The two kidneys filter a nitrogenous waste called uric acid from the blood highly concentrated uric acid travels by ducts called ureters to the cloaca, where along with undigested matter from the intestines, it is excreted in a semisolid, usually white mass copyright cmassengale Respiratory System Air enters through paired nostrils at base of beakDown trachea past syrinx, or song boxenters two primary bronchiito

lungs75% bypasses the lungs and flows directly to posterior to sacssacs connect with air spaces in bones, filling the hollow bones with air When bird exhales the carbon dioxide-rich air from the lungs, oxygen rich air is forced out of the posterior air sacs into lungs via small air tubes copyright cmassengale Circulatory System

4 chambered heart Right and left sides completely separated Right side receives deoxygenated blood from the body and pumps it to the lungs Left side receives deoxygenated blood from the lungs and pumps it to the rest of the body Has a single aortic arch Most birds have a rapid heart beat compared to other vertebrates-Hummingbird-600 times a minute copyright cmassengale Nervous System

Birds have a large brains, relative to their size Cerebellum coordinates movement Cerebrum controls complex behavior patterns such as navigation, mating, and nest building Optic lobe receives and interpret visual stimuli Keen vision is necessary for taking off, landing, spotting landmarks, hunting and feeding Have good color vision Birds large eyes are located near the sides of its head, giving a bird a wide field of vision copyright cmassengale Nervous system

Birds large eyes are located near the sides of its head, giving a bird a wide field of vision Birds with eyes near the front of the head have better binocular vision Hearing important to nocturnal species that rely on sounds to help them locate prey Birds lack internal ears-ear canal leads to a tympanic membrane, called an eardrum Sense of smell is poorly developed except in ducks and flightless birds Sense of taste helps birds avoid bitter-tasting or toxic foods copyright cmassengale 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 ferilized by sperm copyright cmassengale 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 copyright cmassengale Development and Behavior copyright cmassengale 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. copyright cmassengale

Incubation and Development Embryo development begins when the zygote forms a plate of cells on the surface of the yolk. This plate begins to form the tissues and organs

The membrane produces digestive enzymes that dissolve proteins and lipids in the yolk. Blood vessels in the yolk sac membrane carry the nutrients to the embryo. When hatching begins the embryo makes a star-shaped crack in the shell with a scalelike egg tooth. The chick presses and scrapes the shell until the crack widens enough for the chick to emerge. The egg tooth, falls off soon after the chick hatches. copyright cmassengale Incubation and Development

Bird have two contrasting methods for rearing young. Those that lay many eggs and incubate them for long periods hatch precocial young. These birds are active as soon as they hatch, they can walk, swim, and feed themselves. For examples ducks and quail. Birds that lay only a few eggs and hatch quickly produce altrical young. They depend on both parents for several weeks. For ex.

Woodpeckers, hawks, pigeons parrots. copyright cmassengale Behavior The long periods of parental care may enable birds to learn such complex behaviors as courtship, nesting, and migration. Young birds need protection until they develop the strength to fly and obtain food copyright cmassengale Territoriality and Courtship

During the breeding season many male birds establish an area that they defend against other males of their species, a behavior called territoriality. The male then attempts to attract a female to share this territory. Once a territory is established most birds engage in a period of courtship, behavior that is designed to attract a mate. Many males attract females by

means of their brightly colored feathers. Some males combine song with flight displays. copyright cmassengale Nest Building Nests hold eggs, conceal young birds from predators, provide shelter from the elements, and sometimes even serve to attract a mate. Most birds build nests in sheltered, well-hidden spotsfrom holes in the ground to treetops. As a further adaptation to their environment, birds construct their nests of almost any material available. Twigs, grasses, feathers, and mud are the most common

materials used. copyright cmassengale Migration When temperatures drop and the food supply dwindles, these birds migrate to warmer climates. Birds rely on a variety of cues to help them navigate. Some species monitor the

position of the stars or the sun. Others rely on topographical landmarks, such as mountains. Magnetic cues, changes in air pressure, and low frequency sounds may also provide information to migrating birds. The ability of birds to read these cues, along with their many adaptations for flight, enables them to migrate to and inhibit virtually any environment. copyright cmassengale copyright cmassengale

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