Birds are bipedal, warm-blooded, egg-laying vertebrates with about 10,000 living species. The fossil record indicates birds evolved from theropod dinosaurs 200 to 150 million years ago, and the earliest known bird is the late Jurassic Archaeopteryx. There is significant evidence that birds evolved from theropod dinosaurs; as more non-avian theropods that are closely related to birds are discovered, the formerly clear distinction between non-birds and birds becomes blurred. A genetically consistent evolutionary tree would classify birds as reptiles, though some scientists would elevate birds, turtles and crocodilians to their own class, on an equal footing with reptiles.
Globally, 1,223 species of birds, or about 12 percent of the total of 9,998 extant described bird species, were deemed endangered or threatened with extinction by IUCN's 2009 Red List. In the United States, about 74 bird species are at risk, about 9 percent of the total.
Andean flamingo
Ashy storm petrel
Bald eagle
Bicknell's thrush
Black-backed woodpecker
Black-breasted puffleg
Black-capped petrel
Blue-billed curassow
Brown-banded antpitta
Cactus ferruginous pygmy owl
California condor
California spotted owl
Cape Sable seaside sparrow
Cauca guan
Chatham petrel
Chilean woodstar
Coastal California gnatcatcher
Desert nesting bald eagle
Eastern brown pelican
Esmeraldas woodstar
Fiji petrel
Galápagos petrel
Hawaiian petrel
Heinroth's shearwater
'I'iwi
Inyo California towhee
Kittlitz's murrelet
Least Bell's vireo
Lesser prairie chicken
Magenta petrel
Marbled murrelet
Medium tree finch
Mexican spotted owl
Mono Basin area greater sage grouse
Newell's shearwater
Northern goshawk
Northern spotted owl
Okinawa woodpecker
Penguins
Piping plover
Queen Charlotte goshawk
Rota bridled white-eye
Southwestern willow flycatcher
Spectacled eider
St. Lucia forest thrush
Steller's eider
Tricolored blackbird
Western burrowing owl
Western gull-billed tern
Western snowy plover
White-tailed ptarmigan
Xantus's murrelet
Yellow-billed cuckoo
Yellow-billed loon