Probability of Survival and Breeding for Juvenile Female Canvasbacks

Abstract

Few studies have examined factors affecting the probability of recruitment into breeding populations by juvenile ducks. We were able to do this for juvenile female canvasbacks (Aythya valisineria) at Minnedosa, Manitoba, Canada, 1983-1988 by combining estimates of duckling survival, annual survival, and breeding probability. Annual survival probability increased with duckling weight, declined with advancing hatch date, and was lower in years with more liberal than conservative harvest regulations. Breeding probability was lower during years with relatively dry wetland conditions than years with wetter conditions, and it also declined with advancing hatch date. Estimates of breeding probability ranged from 0.54 to 0.94 for juveniles and 0.74 to 0.95 for adults. Recruitment probability for juveniles ranged from 0.12 to 0.28 at the mean of the covariates (body mass and hatch date) and from <0.01 to 0.43 at the extremes. More than 54% of the recruits were ducklings produced in nests that hatched early. The per-capita contribution of recruits by hens that hatch nests early may be even more disproportionate because clutch size and nest success generally decline with advanced laying date. Managers should recognize that late, dry breeding seasons will likely result in poor recruitment of hatched ducklings. Where possible, habitat management should facilitate early nesting by canvasbacks.