APPARENT SURVIVAL RATES OF WESTERN SANDPIPER (CALIDRIS MAURI) WINTERING IN NORTHWEST BAJA CALIFORNIA, MEXICO

To estimate annual apparent local survival, we collected capture–resighting data on 256 individually marked male Western Sandpipers (Calidris mauri) wintering at Estero de Punta Banda, Mexico, between 1994–1997. A hierarchical modeling approach was used to address the effect of age class and year on survivorship rates. The best-fit model included a constant apparent survival probability (ϕ = 0.489; 95% CI = 0.410–0.569), but several models fit nearly as well, and averaging among the top five, to account for model uncertainty, suggested that adults had somewhat higher values than juveniles (ϕ = 0.490 ± 0.051 vs. 0.450 ± 0.067). Detection probability was substantially higher for adults than for juveniles (p = 0.741 vs. p = 0.537). Those apparent survival estimates are low compared with those from other studies of Western Sandpipers at breeding and other nonbreeding locations, and substantially lower than the true survivorship rates expected for small sandpipers in general. We interpret these results as indicating that this site is of below average quality for nonbreeding male Western Sandpipers.