The common poorwill (Phalaenoptilus nuttallii) is a nocturnal bird of the family Caprimulgidae, the nightjars. It is found from British Columbia and southeastern Alberta, through the western United States to northern Mexico. The bird's habitat is dry, open areas with grasses or shrubs, and even stony desert slopes with very little vegetation. Many northern birds migrate to winter within the breeding range in central and western Mexico, though some remain further north. The common poorwill is the only bird known to go into torpor for extended periods (weeks to months). This happens on the southern edge of its range in the United States, where it spends much of the winter inactive, concealed in piles of rocks. Such an extended period of torpor is close to a state of hibernation and is not known among other birds. Taxonomy The common poorwill was illustrated and formally described in 1844 by the ornithologist John James Audubon from a male specimen collected on the eastern bank of the Missouri River between Fort Pierre and mouth of the Cheyenne River in South Dakota. Audubon coined the binomial name Caprimulgus nuttallii, choosing the specific epithet to honour his friend, the ornithologist Thomas Nuttall. The species was moved to its own genus Phalaenoptilus by the American ornithologist Robert Ridgway in 1880. The genus name combines the Ancient Greek meaning "moth" and meaning "plumage". Six subspecies are recognised: P. n. nutalli (Audubon, 1844) – breeds over most of the North American range. P. n. californicus Ridgway, 1887 – dusky poorwill, is darker and browner than the nominate race. It occurs in western California and north Baja California P. n. hueyi Dickey, 1928 – desert poorwill, is paler than the nominate race. It occurs in southeast California, southwest Arizona (USA) and northeast Baja California P. n. dickeyi Grinnell, 1928 – San Ignacio poorwill, is smaller and less heavily marked than californicus. It is resident in southern Baja California. P. n. adustus Van Rossem, 1941 – Sonoran poorwill, is paler and browner than the nominate race. It occurs from extreme southern Arizona to north Mexico. P. n. centralis Moore, RT, 1947 – central Mexico Description This is the smallest North American nightjar, about in length, with a wingspan of approximately . It weighs . The sexes are similar, both gray and black patterned above. The outer tail-feathers are tipped with white, the markings slightly more prominent in the male. The