Effects of microhabitat preferences on Kelp Gull breeding performance

GARCÍA BORBOROGLU, PABLO; YORIO, PABLO

Urbana-Champaign

Congreso; 121st American Ornithologists Union Stated Meeting; 2003

American Ornithological Union

We tested the hypothesis that nest microhabitat preferences are adaptive in Kelp Gulls at one of its largest colonies in Patagonia. We quantified 13 habitat variables at 104 and 92 nest-sites and at 70 and 60 random points in 1998 and 1999, respectively. We recorded egg laying dates, hatching success and breeding success at 92 of these nests in each of the study seasons. Compared to random points, nest sites presented more vegetation cover and were closer to the nearest available bush, but were located farther from the nearest clearing to take flight. Nests were built on substrates with lower slopes and higher percentages of silt-clay, but with lower percentages of rock. In both years, breeding parameters were related to vegetation cover and distance to nearest vegetation. Substrate slope and composition contributed to explain the variation in hatching and breeding success in 1998 and 1999, respectively. Our study shows that some Kelp Gull breeding parameters are affected by nest-site habitat characteristics. These associations were influenced in most cases by the timing of breeding, with earlier breeders being more successful. Vegetation effects and substrate characteristics were important variables in distinguishing random from nest sites and in explaining variation in breeding performance, showing that their preferences appeared to be adaptive and allowing us to detect both the pattern and process in Kelp Gulls habitat selection.