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Abstract

When breeding within densely populated colonies, seabirds benefit from increased offspring protection from predators, but intraspecific competition for resources may outweigh these benefits. We tested whether the number of breeding-site neighbours and days of predator presence influenced the breeding performance of Common Murres Uria aalge at two different-sized colonies off the northeastern Newfoundland coast: Cabot Island (10000 breeding pairs; < 10 km offshore) and Funk Island (500000 breeding pairs; ~60 km offshore). Gulls, the main predators of murre eggs/chicks, inhabit both islands in similar numbers. During July–August 2018, camera traps placed at topographically similar plots on each colony recorded breeding performance metrics (i.e., hatching, fledging, reproductive success), number of breeding-site neighbours, and daily presence of gulls. Hatching success was lower at Funk Island (64.7%) than Cabot Island (96.2%), but nearly all hatched chicks fledged at both colonies. Lower hatching success at Funk Island was due to higher egg abandonment and predation. It was also associated with fewer breeding-site neighbours, including non-brooding mates and non-breeders, along with higher gull presence (96.6% of all gull sightings at both colonies). Fewer neighbours at Funk Island may have resulted from mates and non-breeding murres spending more time at sea due to longer distances to predictable foraging sites and higher conspecific densities relative to Cabot Island. In turn, with fewer breeding-site neighbours at Funk Island, parents appeared less able to defend against or deter gull predation. Although Funk Island has special conservation status, protection of Cabot Island may also be important for the long-term conservation of murres in Newfoundland.

DOI

http://doi.org/10.5038/2074-1235.49.2.1429

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