Apparent survival of adult Herring Gulls (Larus argentatus) occupying two distinct breeding habitats within the East Bay Migratory Bird Sanctuary, on Southampton Island, Nunavut was estimated. The first group occurred on a small island where 30 pairs bred at relatively high densities sympatrically with Common Eider (Somateria mollissima), on whose eggs they feed. The larger group occurred at lower densities on a wet coastal plain on the surrounding Southampton Island mainland, where nesting birds were sparsely distributed. Program Mark was used to analyze capture-mark-resight (CMR) data obtained over six years from 62 adults captured between 1998 and 2002; 47 and 15 nesting on the island and mainland respectively. Factors in models included group and time effects on survival and reduced time effects on encounter probabilities; additional factors and interactions were not tested due to sparse data. High model selection uncertainty and wide 95% confidence intervals around model effect sizes precluded ability to draw inferences concerning the importance of group and time factors in survival. Given these results, focus was placed mainly on an estimate of annual survival (0.87 ± 0.03 SE) from the time- and group-independent model. This is the only known survival estimate produced for Herring Gull adults at the northern limit of their North American breeding range and falls within the wide range of values reported elsewhere.
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