We can already hear you: "Say what? The Common Poorwill hibernates? You have GOT to be kidding. Birds don't hibernate!"
We're not kidding. Named "The Sleeping One" by the Native American Hopi tribe, the Common Poorwill (Phalaenoptilus nuttali) has a tendency to lie around all winter. This small, black and gray nightjar spends the colder months concealed in piles of rocks. It's not completely asleep, like, say a bear; instead, it's very greatly slowed down--a state called "torpor," in which metabolism and body temperature are reduced for days or even weeks. While some hummingbirds experience daily, short-term torpor in order to conserve energy, the Common Poorwill is the only bird known to have long bouts of it, which some scientists call hibernation.
The Common Poorwill is nocturnal, which is rare in itself. Its habitat ranges from British Columbia and southeastern Alberta down to northern Mexico via the western United States. It prefers dry, open areas with grasses or shrubs; it also likes sparsely vegetated, stony desert areas. It is in the southernmost part of its range that the poor-will has most often been seen its long torpor bouts, usually in extremely cold and extremely hot weather, and sometimes even while incubating eggs.
The Lewis & Clark expedition found torpid (or hibernating) Common Poorwills in North Dakota back in 1804. Dr. Edmund Yaeger described them in California in 1948.
In torpor, the poor-will's body temperature as been measured as low as 40°F, with a respiration rate reduced by 90%. That's pretty cool, huh? (In more ways than one.)