"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. Remarkably, 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. This behavior has been reported in California and New Mexico. Such an extended period of torpor is close to a state of hibernation, not known among other birds. It was described definitively by Dr. Edmund Jaeger in 1948 based on a Poorwill he discovered hibernating in the Chuckwalla Mountains of California in 1946.”
(Source: Common Poorwill)
The extended period of torpor is highly unusual — really interesting life history trait!