Colonial seabirds such as alcids often do not rapidly recolonize former breeding habitat following extirpation of nesting colonies. Social attraction (e.g., use of decoys, recorded vocalizations and mirrors) artificially stimulates nesting by providing social cues that encourage colonization. Common Murres (Uria aalge) stopped breeding at Devil’s Slide Rock, San Mateo County, California following the 1986 Apex Houston oil spill. Natural recolonization did not occur between 1987 and 1995. Common Murres began regular visits to Devil’s Slide Rock within 24 hours of social attraction equipment installation in January 1996 and six pairs nested by June 1996. Over 90% of murre observations were in decoy plots in contrast to control plots and outside of plots where few murre observations occurred. Significantly more murre presences versus absences were recorded in low density decoy plots and these birds most often frequented open areas (aisles) within decoy clusters. Significantly larger groups of murres visited high density decoy plots and aisle sub-plots. Murre densities were significantly greater within 30 cm of mirrors. Five of six nests were within 60 cm of mirrors. Nests coincided with areas where prior nesting and last pre-1996 attendance had been concentrated. Rapid breeding response combined with recent nonbreeding attendance suggests that the first colonists may have been surviving breeders from the original colony or young produced at the rock prior to the oil spill. The initial recolonization event and continued restoration efforts have prompted further colony growth to 190 pairs nesting by 2004. This study suggests that social stimuli can limit natural colonization of otherwise suitable habitat.
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Vol. 30 • No. 1