Factors Affecting Duration of Incubation in Black Brant

We investigated factors affecting duration of incubation in Black Brant (Branta bernicla) during 1992 and 1993 on the Yukon-Kuskokwim Delta, Alaska. Duration of incubation varied with clutch size and decreased with later nest initiation. In contrast to other studies, we found no relationship between incubation period and ambient temperature, mean egg size, or nest attentiveness. We hypothesize that a decrease in incubation length with later first egg date is an adaptation by females to reduce disadvantages of hatching late. We suggest that potential costs of reduced embryonic development time outweigh benefits for females that are able to initiate nesting early because their eggs hatch early enough to maximize recruitment of hatched young. For females that nest late, however, advantages to reproductive success of hatching earlier may outweigh costs of reduced development time.