Interactive effects of timing and nest placement on the reproductive performance of the Imperial Shag

SVAGELJ, W. S.; QUINTANA, F.

Victoria, British Columbia

Conferencia; 1st World Seabird Conference; 2010

Pacific Seabird Group and International Steering Committee

Breeding success in seabirds usually declines over the course of the season. Also, the distance of the nest from the edge of the colony has been reported as an important factor affecting breeding success in colonial birds, with peripheral nests usually suffering higher disturbance and depredation than internal ones. We evaluated the influence of timing (laying date) and nest placement (distance to the edge of the colony) on the reproductive performance of the Imperial Shag (Phalacrocorax atriceps) for 632 nests monitored during three breeding seasons (2004, 2005 and 2006) at Punta León, Argentina. Breeding success consistently decreased with laying date during the three seasons. We found an interactive effect between laying date and the distance to the edge of the colony. Such distance was not related to breeding success of shags nesting either early or at the peak of the season. However, the breeding success of the late breeders increased with the distance to the edge. Our results suggest that low-quality (young or less-capable) pairs with low abilities in nest defense that breed late in the season, could take some reward nesting away to the colony edge, diminishing disturbance and/or nest-predation risk.