What North American nocturnal bird is the only bird known to hibernate for months?

The North American nocturnal bird known for entering months-long winter torpor is the common poorwill. Its scientific name is Phalaenoptilus nuttallii, a nightjar found from western Canada through the western United States to northern Mexico.

At the southern edge of its range, some common poorwills shelter in rock piles and remain inactive for weeks or months during cold weather. Their body temperature and metabolism fall substantially, allowing them to conserve energy when flying insects are scarce. Scientists often describe this as extended torpor or hibernation-like behavior because the bird periodically becomes deeply dormant rather than simply migrating.

The behavior was documented in modern science by Edmund Jaeger, who found a torpid poorwill in California in 1946 and published his account in 1948. Meriwether Lewis had recorded apparently hibernating poorwills during the Lewis and Clark Expedition in 1804, but the observation was not understood at the time. The common poorwill is sometimes confused with the whip-poor-will, a different eastern North American nightjar.