SEASONAL REPRODUCTIVE PATTERN OF WHITE-WINGED CROSSBILLS IN INTERIOR ALASKA

It has been proposed that crossbills (Loxia spp.) are opportunistic br eeders that time the onset of their reproductive cycle based on food a vailability rather than photoperiod, as is the case in most other bird species. Crossbills are able to nest throughout most of the year at m iddle latitudes, but the reproductive biology of these birds at high l atitudes remains poorly known. A total of 469 White-winged Crossbills (Loxia leucoptera) was caught in Fairbanks, Alaska during a 2.5-yr per iod. Based on the proportion of juvenile birds in the sampled populati on, the proportion of adult females with a brood patch, and seasonal c hanges in adult male cloacal protuberance size, it appears that interi or Alaska White-winged Crossbills breed only in spring and early summe r. Timing of reproduction of crossbills breeding at high latitudes may be limited by environmental factors (potentially, ambient temperature and/or photoperiod) rather than by food availability.