Breeding biology of Kelp Gulls (Larus dominicanus) at Golfo San Jorge, Patagonia, Argentina

Abstract

The Kelp Gull (Larus dominicanus) is a widely distributed species in the Southern Hemisphere and the third most abundant seabird breeding in Argentina, where it has recently shown an important population expansion. Information on its breeding biology and regional variability will be required if management guidelines for this abundant seabird, with its expanding distribution, are to be prepared. We studied their breeding biology in the north of Golfo San Jorge, Argentina, during 1998 and 1999. The total number of breeding pairs was estimated at 8168 ± 874. Nesting density was variable, depending on habitat, with a mean of 0.14 ± 0.03 nests m−2. First eggs were found on 10 and 13 November in 1998 and 1999, respectively. The median date of laying was the same in both years (21 November). The mean clutch size was 2.32 ± 0.63 and 2.51 ± 0.58 in 1998 and 1999, respectively, and did not differ between years. Egg length, width and volume were similar between years. In three-egg clutches during both seasons, a- and b-eggs of the same clutch did not differ significantly in mean volume, but both were significantly larger than c-eggs. The length of the incubation period was estimated at 26.10 ± 1.74 and 25.88 ± 1.78 days in 1998 and 1999, respectively. Hatching success was similar between seasons (1.70 v. 1.79 chicks per nest). Median hatching date of a-eggs was 19 and 18 December in 1998 and 1999, respectively. The percentage of total chicks lost was 49.67 and 50.78 during 1998 and 1999, respectively. In both seasons the probability of surviving to four weeks of age was similar among siblings. Breeding success was similar between seasons (0.86 v. 0.84 chicks per nest).