Breeding performance of the Imperial Shag (Phalacrocorax atriceps) in relation to year, laying date and nest location
Walter S. Svagelj A C and Flavio Quintana A BA Biología y Manejo de Recursos Acuáticos, Centro Nacional Patagónico – CONICET, Boulevard Brown 2915, Puerto Madryn (U9120ACD), Chubut, Argentina.
B Wildlife Conservation Society, Amenabar 1595, Ciudad de Buenos Aires (C1426AKC), Argentina.
C Corresponding author. Email: tito@cenpat.edu.ar
Emu 111(2) 162-165 https://doi.org/10.1071/MU10062
Submitted: 23 July 2010 Accepted: 26 November 2010 Published: 27 May 2011
Abstract
The breeding productivity of seabirds usually declines over the course of a breeding season. Breeding productivity in colonial birds has also been found to be affected by the distance from a nest to the edge of a colony, with peripheral nests usually having lower productivity than centrally located nests. We evaluated the influence of laying date and nest location (distance from the edge of the colony) on clutch-size and breeding success of the Imperial Shag (Phalacrocorax atriceps) during three breeding seasons (2004–06) at Punta León, Argentina. There was no relationship between year, laying date or nest location and variation in clutch-size. Further, whereas breeding success did not differ between years, breeding success consistently decreased with laying date. We also found an interactive effect between laying date and nest location. Distance from the edge of the colony was not related to breeding success of Shags that laid either early or at the peak of the season, but the breeding success of late breeders increased with distance from the edge of the colony. Our findings of a seasonal decline in breeding success are consistent with the typical pattern exhibited by seabirds. Our results suggest that low-quality (young or less-capable) pairs that breed late in the season may benefit from nesting away from the edge of the colony, reducing levels of disturbance and risk of nest-predation.
Additional keywords: central–peripherial distribution, distance from the edge, parental quality, seabirds, seasonal decline.
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