Components of population growth rate for White-winged Scoters in Saskatchewan, Canada

Abstract

Breeding range and abundance of White-winged Scoters (Melanitta fusca deglandi) have declined in northwestern North America. Hypotheses proposed to account for this trend are that survival and/or recruitment of females had declined. Thus, we used a reverse-time capture-recapture approach to directly estimate survival, seniority and capture probabilities for females of breeding age at Redberry Lake, Saskatchewan, Canada for 1975-1980 and 2000-2003. We also estimated population size of breeding females for 1975-1985 and 2000-2003 using capture-recapture data. Initially, this local population was in serious decline [95%CL(landa75-80) = 0.89 ± 0.09], but has since stabilized and may be slowly increasing [95%CL(landa00-03)=1.07±0.11]. This reversal in trajectory apparently resulted from increased recruitment rather than increased apparent survival. Importantly, recent recruitment of adult females appeared to be driven solely by immigration of adult females with no detectable in situ recruitment, suggesting a hypothesis that the local population is being rescued by females produced elsewhere.