The Vertebrates: Birds (Revised, 1985)

[Music] from the musical notes of a song bird to the rockus call of a seagull the sounds of birds are as distinctive as the birds themselves each type of bird has its own special characteristics and yet there are several ways in which all birds are alike one typical characteristic is the need for Parental care most birds begin life blind and helpless and they must be fed by their parents there are some young birds that are able to move about on their own soon after hatching they can feed themselves but they still depend on their parents for help and protection another way that all birds are alike is that they all share the same basic body structure birds are part of a larger group called vertebrates animals with [Music] backbones in a general way the body structure of a bird is very much the same as that of other vertebrates but the body of a bird is also specialized in several ways some of the bones found in other vertebrates are missing in the skeleton of a bird that helps to reduce body weight other bones are combined making the body more rigid and more efficient as a flying machine another special adaptation is the structure of the bones themselves most of them are Hollow that reduces weight still further without sacrificing strength a bird has a large breast bone that sticks out in front providing a place for the attachment of the powerful Wing muscles these large muscles May account for as much as half of the total body weight there are several other characteristics that help birds to fly birds are the only animals with feathers most of the body is covered with contour feathers they're important for flying because contour feathers help give the body its streamlined shape the feathers actually used in flying are called quill feathers they're found on the wings and the tail the quill is a rigid shaft that provides the support needed at the base of the feather the upper part of the feather is called the vein this part is flexible but still firm under a magnifying glass you can see that the vein is made up of many long thin segments these are called barbs along the edge of each Barb are small branches called barbules with hooks that hold the barbs together if the barbs separate the bird can hook them again by using its beak to pin the feathers this is how it works something like a zipper with the barbs joined together the feathers form a broad surface that pushes against the air and moves the bird forward the outer parts of the wing feathers Bend as the wing moves and the action is something like the Turning of a [Music] propeller Wings feathers and Powerful flight muscles give a bird the ability to fly and this ability is reflected in other adaptations of a bird's body to direct its flight especially at high speeds a bird needs Keen eyesight the eyes of a bird are much larger in proportion to body size than the eyes of any other [Music] animal most of the eyeball is hidden within a socket of bone in the skull the retina of a bird's eye eye is densely packed with visual cells forming an image that's as much as eight times as sharp as the image on a human retina a bird has three eyelids there are two outer eyelids like those of many other animals usually these two are closed only for sleeping the third eyelid is used for blinking it moves sideways cleaning and moistening the eye since this third eyelid is transparent a bird can see even while blinking owls are the only exception they blink with the upper eyelid as well as with the inner transparent one Keen eyesight helps a bird to find food and to evade Predators as well as to direct its course as it flies another requirement for flight is energy it takes a great deal of energy to overcome the force of gravity and birds have several adaptations that help to supply The energy they need it begins with the food they eat some birds feed mainly on Plants many parts of a plant are mostly bulk with very little food value but there are certain parts like seeds and fruit that are rich in food energy and these are the parts that are most often eaten by birds other birds feed on insects worms or other animals this kind of diet is rich in protein which is a highly concentrated form of food also important is the fact that a bird has a rapid and efficient digestive system food can be transformed very quickly into the energy that a bird needs in order to fly and a bird also uses energy from food to maintain a high body temperature that's why birds are called warm-blooded animals a characteristic that they share only with mammals because birds are warm-blooded they can remain active in Winter as long as they can find enough food to maintain their body temperature some food may be stored as a layer of fat and that helps to provide insulation and prevent the loss of body heat birds have more feathers in Winter than they do in summer and Feathers give additional protection from the cold in fact feathers provide even better insulation than the fur of a mammal in Winter as well as in summer most birds maintain the same high body temperature depending on the species that temperature is in the range of about 104 to 108° F or 40 to 42° C several degrees warmer than the body temperature of an average mammal Birds also have a more rapid heartbeat than mammals this rapid heartbeat helps maintain their high body temperature and provide the energy they need for flying so all birds are alike in many ways and yet each type of bird is adapted in its own way to a particular environment and way of life there are birds that are able to soar to ride on on currents of air flying with little or no movement of their wings some birds have long narrow wings that are well suited for soaring at low altitudes over the ocean this kind of soaring depends on variations in the horizontal winds that blow across the water there are other birds that soar over land these birds have broad wings and they soar at high altitudes riding on the vertical currents of air that rise over warm ground other birds have wings that are adapted for long-distance flying as they migrate with the changing [Music] seasons geese and some other birds have long wings that make it possible to fly at high speeds the large breast muscles of these birds are well supplied with blood vessels and that makes it possible for the muscles to produce the continuous energy needed throughout the [Music] flight there are other birds that spend most of their time on the ground pheasants and other ground birds have large flight muscles but those muscles have very few blood vessels so they can't produce enough energy for sustained [Music] flight these ground birds can fly for only a short distance but their short powerful wings are well adapted for making a quick escape from a predator Penguins aren't able to fly at all at least not in the usual sense they use their short stubby wings and Powerful breast muscles in swimming Penguins actually fly through the water ostriches aren't able to fly but they can move rapidly on the ground an ostrich can escape a predator by running at a speed as fast as some birds fly ostriches are so well suited to life on the ground that they don't need to fly their powerful legs and feet are adapted for walking and running and also for kicking which is another way that ostriches protect themselves the feet of other birds also have special adaptations a perching bird has three toes in front and one in back strong muscles in the legs lock the toes in a firm grip that keep the bird on its perch even while asleep a climbing bird has only two toes in front but it has two back Toes that help to brace the bird as it climbs meat eating birds have toes with sharp talons used to capture and hold their prey many water birds have webbed feet that act as paddles in swimming some ground birds have feet with claws that are adapted for scratching the ground in search of food the beak of a bird is also adapted to a specific way of life some birds like a cardinal have heavy beaks used in cracking hard seeds the long slender beak of the hummingbird is used to sip nectar from flowers Birds of Prey have sharp hooked beats well suited to tearing meat a crane like other waiting Birds uses its long beak to probe the water and catch fish and other small animals and the broad spoon-like beak of a duck is used as a strainer most Ducks feed on underwater plants and they hold the food in their beaks until the water is drained out through the sides in the shape and use of the beak and in many other ways each type of bird is adapted to its environment and its way of life birds can be found in almost every kind of environment on the earth that's possible in part because of the special adaptations of each type of bird and also because of the characteristics that all of them share characteristics that give nearly all birds the ability to fly [Music]