Main->Readings->4th Grade Readings->Table of Contents->Part 5: Birds
Vocabulary |
The earliest fossils of birds had many things in common with dinosaurs. They had teeth, claws, and tails as well as wings and feathers. Dinosaur fossils have been found which may have feathers, (although soft body parts do not fossilize well). There are other ways dinosaurs and early birds seem to be similiar. Therefore, many scientists believe that birds descended from dinosaurs. Like everything else in science, this belief is a theory, a way of explaining the facts. Whether or not this is true, it is also probable that dinosaurs and birds both evolved from reptiles.
The oldest fossils of birds are around 290 million years old. Like reptiles, they have lungs. Their eggs, like reptile eggs, contain food and have a hard outer covering so the eggs can be laid in dry places. However, birds are even better at living on dry land (or dry air) than reptiles.
Birds are warm-blooded. Their body temperature stays the same no matter how cold or hot it is outside. Their feathers also help keep them from losing body heat. This means that birds can live in very cold places where reptiles cannot survive. In order to stay so warm, they must eat more than reptiles. However, they are also more active and can move about more than reptiles can.
Birds have larger brains and are more intelligent than reptiles or amphibians. Birds also have two other traits which help them survive well. One is flight, and the other is their life cycle.
Although there are some birds which do not fly, such as the penguin and the ostrich, most birds are adapted for flight. They have light, hollow bones, and they balance on their back limbs while their front limbs have adapted to become wings.
Feathers, important for flight and warmth, are similar to hair and scales. Like hair and scales, they are made from a substance called keratin and grow from the skin. A feather has three main parts:
Because they can fly, birds can live in places no other vertebrate could reach. Some birds live most of their lives miles out over the ocean. Others live on cliff faces, or in the tops of tall trees. Many birds migrate long distances during the year.
Flight is common in birds and insects, but unusual in other animals. Some animals "parachute," or fall slowly, while others glide (like flying squirrels and flying fish). Bats, like birds, can flap their wings and rise into the air, but only birds can soar.
Birds lay fewer eggs than reptiles, sometimes only one or two. Although this would not be a good idea for reptiles, which do not raise their young themselves, it works out for the birds. This is because birds feed and protect their young from the moment the eggs are laid until the young birds are ready to go out on their own. Most birds build nests of some kind for their eggs. Nests act as protection and camouflage from predators. Often, both the parents care for the young, and many birds, unlike reptiles, pair for life. The life of a bird is hard work!
Questions: For your first assignment of the week, answer these questions in complete sentences on a sheet of loose-leaf paper, with a proper header:
Notes: For your second assignment of the week, in your journal on the next clean page, write the vocabulary words from this section and their definitions.
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Go on to Part 6: Mammals
This page last modified November 18, 2002
Copyright ©2000 Delia Marshall Turner. All rights reserved.
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