Nest-site selection and characteristics in a mixed- species colony of Avocets Recurvirostra avosetta and Black-winged Stilts Himantopus himantopus

particular location for nesting from all possible sites (Burger 1985). The exact location of a nest may have important consequences for breeding success, for example influencing predation risk (Regehr et al. 1998) or probability of flooding (Lauro & Burger 1989). Consequently, birds carefully choose nest-sites in order to maximize their possibilities of a successfully breeding outcome. Nest-site selection has been studied in many bird species, both solitary (Burger 1987) and colonial breeders (for example seabirds; Buckley & Buckley 1980). When choosing nest-sites, birds must consider the proximity of feeding areas, shelter and protection or camouflage against predators. In the case of colonial birds, they must add social factors, strongly influenced by the relative position of the nest within the colony and distance to neighbouring nests. Different factors can produce different or opposite selection pressures (Spear & Anderson 1989, Burger & Gochfeld 1990), and nest-site selection becomes a compromise depending on what factors most strongly determine nesting success in each circumstance. Nest-site selection and nest characteristics in Avocets Recurvirostra avosetta and Black-winged Stilts Himantopus himantopus were investigated in a large mixed-species colony. The aim was to compare nest size and nest location between the two species and to test whether there are inter-species differences that might suggest specific nesting adaptations. A second aim was to investigate possible correlates between hatching success and nest location. In relation to hatching success and causes of breeding failure, three predictions were made: (i) flooded nests are closer to water than successful ones, (ii) depredated nests are further from the centre of the colony than successful ones, and (iii) depredated nests are closer to dry land than successful ones if predation is mainly due to terrestrial predators. Bird Study (2004) 51, 20–24