Survival, Productivity, and Abundance in a Wilson's Warbler Population

We analyzed patterns in the abundance, productivity, and survivorship of a coastal California population of Wilson's Warbler (Wilsonia pusilla) using capture-recapture data from 18 years of standardized mist-netting conducted during the breeding season. The numbers of adult and hatching-year birds captured each year showed no consistent trend through time. The total number of adults captured annually, an index of adult abundance, was positively related to productivity in the previous year as indexed by the number of hatching-year birds captured. In addition, the number of adults captured for the first time at the study site, an index of new adults entering the population, was positively related to the previous year's productivity. There was a positive correlation between the numbers of summer residents and transients captured in each year. Estimated annual adult survival of summer residents was 50.3%. The annual recapture probability for summer residents (68.8%) was much greater than for presumed transients (7.2%). When the difference in recapture probability between summer residents and transients was ignored, annual survival was underestimated (30.5%). Year-to-year variation in survival showed no relationship to annual fluctuations in adult abundance. These patterns of survival and productivity parameters suggest that abundance in this population has been influenced primarily by circumstances on the breeding grounds.