| Summary: | We estimated first-year and adult survival of Black Brant (Branta bernicla nigricans) from the Yukon—Kuskokwim Delta, Alaska, to assess (1) the role that first-year survival plays in declining recruitment and in the local breeding population's decline since the early 1980s and (2) the potential role of subsistence harvest in declining first-year survival. We used band-recovery models in program Mark to estimate band-recovery rates and annual survival from 1986 to 2007. The only models of band recoveries that received support contained annual variation and an additive effect of sex on band-recovery rates. The two best-supported models of annual survival differentiated between first-year and older Black Brant. The best-supported model (Akaike weight = 0.69) included a linear trend in first-year survival, while the second best-supported model (Akaike weight = 0.20) included an effect of mean gosling mass on first-year survival. Band-recovery rates corresponded to harvest rates of ∼1%, indicating that during the study period harvest was not demographically important. Adult survival was comparable (0.87) to that from other studies of this population, while first-year survival declined from 0.46 in 1986 to 0.24 in 2007. The trend of decline in first-year survival represented the effects of variation in conditions for goslings' growth in the breeding area combined with unknown effects on migration and in the wintering areas. Declining first-year survival is an important contributor to decline in the local breeding population of Black Brant.
|
|---|