OutdoorNebraska

W hat makes a bird a bird? Well, there's the fact that birds can fly. But so can bats, and bats are mammals. Birds lay eggs. But so do reptiles, fish and amphibians. Birds are endothermic, meaning their body temperature remains the same at all time. But mammals are endothermic, too. So what makes a bird a bird? There are three things that make birds unique: they lay hard eggs, they have hollow or nearly hollow bones, and they have feathers. Laying Hard Eggs Like reptiles, amphibians, fish, and the platypus, birds lay eggs. Within all of these eggs is a developing embryo that eventually will hatch. But unlike most reptiles, amphibians and fish, birds incubate their nests. This means the mother – and sometimes the father – sit on the eggs to keep them warm. If the eggs get too cold, the embryo inside could die. Because birds sit on their eggs, the eggs must be sturdy. This is why bird eggs have hard shells. A bird egg shell is made of calcium. Birds get some of this calcium from seeds, plants and insects. But new research shows that many birds will eat old egg shells, snail shells and rocks containing calcium to ensure they have enough calcium to produce strong eggs. All this calcium is deposited around the egg just before it is laid. This calcium is also important for the developing embryo to be able to grow strong bones. Hollow Bones Bird bones are not hollow like a straw, but they are not solid like mammal bones, either. Bird bones are somewhere in the middle. Their bones have a hard exterior or outside, just like mammal bones. But the inside of a bird's bones is filled with a network of structures to support the hard outside. Between these network structures, the bone is filled with air. This helps make the bone strong but light in weight. Having light bones is important as a bird tries to fly. Imagine trying to lift your whole body off the ground by flapping your arms. We can't do it because we are too heavy. Birds are very light weight. When they flap their wings, they can easily lift their whole body up and even fly for hours. Feathers Many species are characterized by their body coverings: reptiles have scales, mammals have fur, and birds have feathers. But all feathers are not created the same – or for the same reason. A bird has many different kinds of feathers. The down feathers are the fluffy feathers that are often under the body feathers. HOLLOW AREAS SHOWN IN GRAY What Makes a Bird a Bird? American Robin 4 — BIRDOLOGY: A Kid's Book About Birds

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