Hatching success in Avocet Recurvirostra avosetta and Black-winged Stilt Himantopus himantopus

Abstract

Capsule Daily survival rate of nests was influenced by laying date and nesting period (laying versus incubation) in both species and by colony size in Black-winged Stilts. Aims To investigate the effect of clutch size, colony size, reproductive phenology and nesting period on hatching success of Avocets and Black-winged Stilts. Methods The study was undertaken at two localities in southwestern Spain (Doñana and Odiel Natural Parks) during 1990 and 1991 breeding seasons. The Mayfield method was used to estimate hatching success. Results Both species bred colonially and some colonies included nests of both species. Neither year, locality, species or clutch size had a significant effect on hatching success. Daily survival rate was lower for late nests than for early and intermediate, and lower during egg-laying than during incubation in both species. Hatching success of Black-winged Stilt nests was lower in large colonies (>50 nests) than in medium-sized ones (11–50 nests). Conclusion Late clutches within a colony (clutches with the least hatching success) might be replacements or belong to late breeders, but adults were not individually marked, precluding clarification. The results suggest a high probability of clutch predation and/or desertion in early stages of the nesting period, especially shortly after laying the first egg. The fact that hatching success in large colonies was lower than in medium-sized ones, but only for Black-winged Stilts (not for Avocets), might help to explain the difference in coloniality of the two species.