BREEDING BIOLOGY OF THE COMMON POORWILL AT THE NORTHERN EDGE OF ITS DISTRIBUTION

The breeding biology of Common Poorwills (Phalaenoptilus nuttallii) wa s studied from 1989 to 1992 in the Okanagan Valley of British Columbia and 1991 to 1992 in the Cypress Hills of Saskatchewan, Canada. Indivi duals were captured by luring them into mist nets using song playbacks . Data were collected from a total of 27 nests (from 17 pairs), found by following birds outfitted with radio transmitters. Poorwills arrive d from mid-April to late May. Four of five pairs in British Columbia a nd two of three pairs in Saskatchewan made two nesting attempts each. Poorwills appeared to be monogamous and the pair bond, with one except ion, was maintained throughout the breeding season. First clutches wer e laid from late May to late June and second clutches from early July to early August. Nest initiation was approximately 2 wk earlier in Bri tish Columbia than in Saskatchewan. Twenty-six of 27 clutches consiste d of two eggs. Both male and female birds shared incubating and broodi ng responsibilities, although males were found incubating significantl y more often, whereas females brooded significantly more. The incubati on period was 20-21 d. Hatching success was 63% in British Columbia an d 71% in Saskatchewan. The nestling period was 20-22 d. Fledging succe ss was 8% and 30% for British Columbia and Saskatchewan, respectively. Predation appeared to be the most important factor limiting reproduct ive success.