The Life of Birds

adaptation Adelie Penguin adult altricial American American Robin animal Archaeopteryx avian beak behavior bird's blood body bones breeding season brood build cells cent Chaffinch chicks cies clutch colony color courtship Cuckoo cycle ducks eagles ecologic eggs European European Robin example feathers feeding female Figure finches flight flycatchers flying glands grebes Grouse gulls habitat hatching hawks hormones House Sparrow House Wren hummingbirds incubation insects instinctive islands kilometers legs living male mammals mate ment metabolism meters migration migratory molt muscles natural selection nest nestlings normal North owls pair parasites parents passerines penguins petrels Photo pigeons plumage population predators probably regions reproductive reptiles Robin Ruffed Grouse sea birds singing Song Sparrow South America species of birds Starlings stimulate storks Stresemann swallows temperature terns territory Thrush tion tive trees tropical Turdus tyrant flycatchers Warbler weight wings winter woodpeckers Wren young birds