SURVIVAL OF JUVENILE BLACK BRANT DURING BROOD REARING

Survival of young is an important and poorly understood component of w aterfowl productivity. We estimated survival of black brant (Branta be rnicla nigricans) goslings during summers 1987-89 on the Yukon-Kuskokw im Delta, Alaska, to determine timing and magnitude of gosling mortali ty and to compare methods of estimating gosling survival. Eighty-two p ercent of radio-tagged adult females (n = 61) fledged greater than or equal to 1 gosling (brood success). We estimated survival of goslings within broods by 3 methods: (1) changes in mean brood size through tim e, (2) observation of goslings associated with marked adults, and (3) age ratios of brant captured in banding drives. Estimates of gosling s urvival within successful broods averaged 81% and ranged from 66 to 92 %. Combining brood success and gosling survival within successful broo ds yielded estimates of overall gosling survival that averaged 68%, ra nging from 79% in 1987 to 56% in 1989. Eighty-two percent of gosling m ortality occurred in the first 15 days. Estimates of survival on the b asis of age ratios of birds captured in banding drives are biased low. Our estimates of average gosling survival are higher than reported fo r other species of geese.