REPRODUCTION CONSTRAINS THE USE OF DAILY TORPOR BY FREE-RANGING COMMON POORWILLS (PHALAENOPTILUS-NUTTALLII) (AVES, CAPRIMULGIDAE)

The purpose of this study was to determine if common poonwills (Phalae noptilus nuttallii) resist entering torpor during the breeding season. During the summers of 1991 and 1992, we studied poonwills in the Cypr ess Hills, Saskatchewan, Canada, near the northern limit of their dist ribution. Since poorwills are monogamous and share incubating and broo ding responsibilities, we predicted that the non-incubating or non-bro oding bird would enter torpor when stressed energetically (e.g. on col d and/or wet nights). Individuals carrying temperature-sensitive radio transmitters entered torpor significantly less often during the breed ing season (two of 195 bird nights) than the non-breeding season (27 o f 44 bird nights). During the breeding season we found no birds involv ed in an active nesting attempt in torpor. We conclude that reproducti on constrains the use of torpor by adult birds, but why non-incubating and non-breeding birds did not enter remains unclear.