| Summary: | The influence of nest location, terrain, social environment (e.g., nesting density), breeding synchrony and foraging effort on the reproductive success of Common Murres (Uria aalge) nesting at Castle Rock National Wildlife Refuge in northern California (2009–2010) was examined. Robotic video cameras were used to minimize the effects of human disturbance. Individual nest sites were selected and observed though the nesting season to determine timing and success of breeding. Adult behaviors were used to index foraging conditions. Murres at Castle Rock had relatively high breeding success (69%) both years of the study. Nest site characteristics and adult behaviors that influenced success varied between the incubation and chick-rearing periods and between years, although breeding synchrony influenced both hatching and fledging success. Hatching success was influenced by nest site terrain, social environment and laying synchrony. Nest sites were more likely to fail during the incubation period if they were located on even substrates or along the edge of a group of sites. The occurrence of site flooding had a pronounced effect on hatching success: nest sites where flooding was observed were 5.2 times more likely to fail in 2009 than nest sites where flooding was never observed. Eggs that hatched late relative to all observed nest sites were also more likely to fail than eggs that hatched early or during the peak of hatching. Fledging success was influenced by social environment, hatching synchrony and foraging effort. Nest sites with fewer breeding neighbors were more likely to fail, as were nest sites where adult aggression was never observed. Most notably, chicks that hatched late relative to other nest sites in the immediate vicinity and relative to all observed nest sites were approximately 4 and 7 times more likely to fail, respectively, than nest sites that hatched early or during the peak of hatching. Although opportunistic predation may have accounted for nest failures at isolated or exposed nest sites, the ...
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