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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 (Donana 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 ...

Capsule Causes of breeding failure determined optimal nest location, Black-winged Stilts being better adapted than Avocets to nest close to water. Aims To compare nest size and location between the two species and to test whether there were inter-species differences that might suggest specific nesting adaptations, and to investigate possible correlates between hatching success and nest location. Methods Nest-site selection, characteristics and hatching success were studied during 1989 in a large mixed-species colony located in southern Spain. Results Black-winged Stilt nests differed in composition and size depending on distance to water (nests touching the water were larger and included mud), but Avocet nests did not. Avocets nests were more aggregated and central within the colony than those of Black-winged Stilts. Causes of breeding failure were flooding and rat predation. Successful or unsuccessful Black-winged Stilt nests did not differ significantly in characteristics or location. Successful Avocet ...

Because Gulls have been considered to reduce Avocet breeding success, the behaviour of Black-headed Gulls Larus ridibundus and Avocets Recurvirostra avosetta at Havergate Island, Suffolk, was analysed in order to compare the effects of two methods of Gull productivity control, (a) formalin injection of eggs and (b) nest raking. Of four lagoons, two were controlled by each method in a simple experimental design. Gulls breeding on different lagoons behaved similarly prior to control, although Avocets showed no such consistent pattern. During the period 0–60 min after control Gulls were significantly more active on the ‘raked’ lagoons than on those where clutches were injected, in which they returned to their nests. This difference between lagoons was long-lasting — Gulls from ‘raked’ lagoons showed significantly more disturbed behaviour and exhibited a greater frequency of aggression, both interspecific and intraspecific, during the 2-month period of the experiment. There were no determinable effects of tre...