8.1 Birds

1. 8.1 Birds

2. Objectives • Describe the main characteristics of birds. • Explain how birds are adapted for flight. • Interpret how the shape of a bird's wings helps a bird fly. • Compare and contrast bird reproduction and reptile reproduction.

3. As fliers, birds can easily escape enemies and cover large areas in their search for food. • They can move over great distances to find good feeding or breeding sites. • For these reasons, birds have been able to make many kinds of habitats home.

4. Characteristics of Birds • Like reptiles, fishes, and amphibians, birds are vertebrates. • But birds are different from these other vertebrates in an important way. • They are endotherms, organisms that have a constant internal body temperature.

5. Reptiles and amphibians obtain heat from their external environment. • When it is cold out, they are sluggish. • Birds, however, can be active no matter what the temperature of their environment. • For this reason, birds inhabit nearly all parts of the earth.

6. All birds share certain other characteristics, too. • You can probably guess what most of them are. • Birds are the only group of animals to have feathers. • They have beaks instead of teeth. • Although not all birds can fly, all birds have wings. • And, like reptiles, birds lay eggs with shells.

7. Origin of Birds • One day in 1861, a man in Europe split apart two layers of rock in a quarry. • Inside he found the fossil imprint of an amazing organism.

8. Like a reptile, it had scales, jaws with teeth, and claws on its front limbs. • But also visible in the stone was the unmistakable imprint of feathers. • The 150-million-year-old fossil was an ancient bird! • Scientists called it Archaeopteryx CAR kee OP tur ihks).

9. The fossil of Archaeopteryx was evidence that birds may have evolved from a reptile ancestor. • Since then, other evidence has been collected to back up this conclusion. • But scientists still don't know the exact evolutionary relationship between reptiles and birds.

10. They think that feathers evolved from reptile scales, but they don't know why. • There had to be some in-between animal that couldn't fly but that could take advantage of having feathers. • Perhaps the first birds were fast runners who used their feathered wings to catch insects.

11. Diversity of Birds • There are almost 9,000 species of birds. • Types of birds include birds of prey, perching birds, water birds, and flightless birds.

12. Even within a group, birds have an amazing variety of shapes and sizes. • Each bird is adapted to eating a certain kind of food and living in a certain kind of habitat. • A bird's lifestyle is reflected in its beak, wings, and feet.

13. Birds of Prey • Birds of prey eat mammals, fish, and other birds. • They have sharp, hooked beaks good for tearing flesh,and claws made for grasping. • Birds of prey include eagles, hawks, owls, falcons, and vultures.

14. Water Birds • The different types of water birds have varied beaks, wings, and feet. • Many have webbed feet for swimming. • Other water birds, like this flamingo, have long legs for wading. • Some have long bills for digging food out of the mud.

15. Insect-Eating Perching Birds • Many perching birds are insect eaters. • They have long, pointed beaks that work like tweezers. • The beaks of woodpeckers are used as drills for boring into wood to find insects. • Swifts have wings that let them fly fast and turn quickly in pursuit of flying insects.

16. Flightless Birds • Flightless birds have lost the ability to fly. • They have lifestyles that make flight unnecessary. • Many flightless birds, such as this rhea, have become fast runners.

17. Seed-Eating Perching Birds • Other perching birds are seed eaters. • Seed-eating birds like this cardinal have thick, strong beaks for cracking open seeds.

18. Adaptations for Flight • Like airplanes, birds must be streamlined to fly. • Their bones must be lightweight. • In addition, they must use large amounts of energy, just as an airplane uses fuel. • A bird's body releases the energy stored in food quickly and efficiently.

19. Its cells do this work at a much faster rate than the cells of reptiles and amphibians. • In the process, they create more heat. • The extra heat produced by cells rapidly using fuel makes birds endothermic. • Adaptations for low weight and high activity are present in all parts of a bird's body.

20. Vision

21. Muscles

22. Bones

23. Digestive System • Birds must take in a large and steady amount of food to meet their high energy needs. • The crop stores food and releases it in a steady stream for digestion. • A special organ, called the gizzard, grinds up the food to make it more easily digested in the intestine.

24. Air Supply • To provide the blood with as much oxygen as possible, birds have a special breathing system. • In addition to lungs, air sacs increase the amount of oxygen a bird can take in.

25. Heart

26. Feathers • Feathers are perhaps a bird's most important adaptation. • Without feathers birds could not fly no matter how light their bodies. • A contour feather is both strong and light. • These feathers together make up most of a bird's wings and tail, the most important structures in flying.

27. Shorter contour feathers cover a bird's body, making it streamlined. • Contour feathers have many rows of interlocking barbs. • These barbs are what make a feather strong and firm.

28. Under the contour feathers and next to a bird's body are down feathers. • The fluffiness of down feathers traps a layer of air next to the body. • This layer of air prevents heat loss. • Birds could not maintain body heat at high altitudes or in cold climates without the insulation of down feathers.

29. Physics of Flight • Birds use their wings to push themselves through the air. • But if birds relied on flapping alone, they would tire quickly. • Flying is made easier because wings provide lift, even without being flapped. • The key is in the shape of the wing.

30. You may have noticed that an airplane's wings are not flat. • The upper surface is rounded. • When a wing with this shape moves through air, the air has a longer way to go around the curved upper surface than it does across the flat bottom surface. • The air above the wing must move faster to cover this longer distance in the same amount of time.

31. This difference in air speed above and below the wing creates a difference in air pressure. • The pressure under the wing is higher. • So there is more force pushing up, under the wing, than there is force pushing down, on top of the wing. • The result is lift.

32. The larger the wing, the greater the lift. • Birds with large wings can soar and glide for a very long time. • Once they are airborne, they can cover great distances without flapping.

33. Migration • In places where winters are cold, many animals face a shortage of food for part of the year. • Plants stop growing.

34. Insects and other invertebrates die or bury themselves. • Some animals deal with the shortage of food by becoming inactive, or hibernating. • Birds, however, can go somewhere else to find food.

35. Taking advantage of their ability to fly, many birds migrate, or move to a different place during part of every year. • Some birds in the northern hemisphere, for example, fly south to warmer places for the winter months.

36. When migrating, many birds travel along certain flying routes. • Many of these routes follow coastlines, sea currents, wind currents, or land contours.

37. Some migrating birds travel distances that are hard to imagine. • The short-tailed shearwater flies upto 32,000km every year, circling the Pacific Ocean. • The arctic tern enjoys the endless days of arctic summers, then flies all the way to Antarctica in time for summer!

38. Reproduction of Birds • Birds reproduce much like their nearest vertebrate relatives, the reptiles. • The male passes sperm to the female, and the eggs are fertilized inside her body. • Shells form around the eggs. • Then the female moves the eggs outside her body for the embryos to develop.

39. Unlike reptiles, however, birds have eggs that must stay warm while the embryos develop. • Birds must therefore incubate their eggs, or use their body heat to keep the eggs warm. • The need to incubate their eggs causes birds to have reproductive behavior different from that of reptiles.

40. Incubation can't be interrupted for long. • How does one bird incubate its eggs and find food at the same time? • In some species of birds, the male and female take turns sitting on the eggs.

41. In other species, one of the parents sits on the eggs and the other finds food for both of them. • Either kind of cooperation requires an attachment,called a pair-bond, between male and female. • Not all birds have pair-bonds.

42. To help keep the eggs warm and protected, birds build nests. • In contrast, most reptiles bury their eggs in soil. • The nests of many kinds of birds are very complex structures. • In many species, nest making is shared by males and females. • This is another reason for pair-bonding.

43. Bird eggs have a hard shell compared to the leathery shell of reptile eggs. • The hard shell keeps the embryo from being crushed during incubation.

44. Along with the embryo, a bird egg contains yolk and albumen. • The albumen is the "white" of the egg. • The yolk provides most of the food for the embryo.

45. At the end of the incubation period, the chick breaks open the shell. • The chicks of some species are fully developed when they hatch. • They are ready to move and find food. • In other species, the chicks are blind, helpless, and almost featherless. • They must be fed and taken care of by one or both parents before they are ready to be on their own

46. End