NUMBERS, BREEDING CHRONOLOGY, AND BREEDING SUCCESS OF COMMON MURRES AT BLUFF, ALASKA, IN 1975-1991

In 1979-1991, midsummer counts of Common Murres (Uria aalge) at Bluff, Alaska, showed no overall trend but varied in relation to weather con ditions on the days of the counts within years and also varied markedl y among years in relation to spring weather conditions, timing of bree ding, and the number of actively breeding pairs. The high variability in annual mean counts during a period when there was no overall change in numbers indicates that annual differences in counts may reflect di fferences in colony attendance of adults rather than changes in popula tion size. Both breeding chronology and reproductive success varied am ong years: breeding chronology was most advanced and reproductive succ ess was highest in years when spring air temperatures were highest. An nual variations in numbers, breeding chronology, and breeding success paralleled those for Black-legged Kittiwakes, but the magnitude of var iability in murre numbers and breeding success was much lower than tha t of kittiwakes. Breeding chronology of Common Murres was earlier at B luff than at coastal colonies north of Bluff and island colonies in th e central Bering Sea; however, comparisons with other studies indicate that there are no easily discerned geographic patterns. Although Bluf f is near the northern limit of the breeding range of Common Murres in the eastern Pacific Ocean, there is no evidence of adaptations to sho rten the duration of breeding attempts or of a shortened breeding seas on. In contrast to studies of Common Murres elsewhere, we found that r eproductive success did not decline seasonally and breeding success of replacement attempts equaled that of first attempts. Both the very ea rliest and latest attempts were unsuccessful each year, however, indic ating stabilizing selection on the laying dates of murres at Bluff.