Local survival of marbled murrelets in Central California: Roles of oceanographic processes, sex, and radiotagging

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Journal of Wildlife Management
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We estimated annual local survival rates for after-hatch-year (>= 1-yr old) marbled murrelets (Brachyramphus marmoratus) in central California using Cormack-Jolly-Seber mark-recapture models and radiotelemetry, and we modeled the effect of oceanographic conditions, sex, and radiotagging. We captured 331 after-hatch-year murrelets from 1997 to 2003, of which 117 were radiotagged. Recapture rates were best modeled using a term that reflected differences in capture effort among sampling occasions (p(effort)) and ranged from 0.068 to 0.166. The most highly ranked Model (Phi(PDO+radio,) P-effort) indicated that survival rates were positively related to the strength of the Pacific Decadal Oscillation (PDO) and were negatively affected by radiotransmitters in the year following tagging. Mortality was relatively low in warm-water years, perhaps because murrelets flew inland to breed less frequently and were less exposed to avian predators. Two competing models indicated that survival in the year following tagging was affected by (1) only radiotagging (model Phi(radio), p(effort)), and (2) radiotagging and sex (model Phi(sex+radio,) p(efford)). Model-averaged survival estimates were 0.868 (SE = 0.074) and 0.896 (SE = 0.067) for males and females, respectively, that were not radiotagged and 0.531 (SE = 0.175) and 0.572 (SE = 0.181) for males and females, respectively, that were radiotagged. Mortality of radiomarked individuals was greatest during a domoic acid (a neurotoxin in the marine environment) bloom in 1998 (Phi = 0.160-0.400) and radiomarking impacts were much less pronounced during typical years (Phi = 0.724-0.810). Additional causes of mortality included predation by peregrine falcons (Falco peregrinus) and oil spills. Survival for nonmarked individuals was similar or higher than what was estimated for murrelets in British Columbia and what was predicted for murrelets based on comparative analyses of other Alcid species, suggesting that mortality of after-hatch-year murrelets is not an immediate threat to population viability in the region.


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