Habitat Selection and Nesting Association in Four Species of Charadriiformes in the Po Delta (italy)

SU M M A R Y. —Habitat selection and nesting association in four species of Charadriiformes in the Po Delta (Italy). Colony, nest site selection and interspecific associations of four breeding Charadriiformes were studied in the Po Delta, Italy, in 1991. Physical characteristics (such as length, size, distance from mainland and other islands, occurrence of small dunes, etc.) of eighteen islands and two peninsulas were considered; random points were selected on the islands, and several parameters (such as distance from the shore, apparent elevation above sea level, vegetation cover, kind of substrate, etc.) compared with those of a similar number of nest sites. Apart from Yellow-legged Gulls Larus cachinnans, which selected the longest and largest islands, the other species (Oystercatchers Haematopus ostralegus, Kentish Plovers Charadrius alexandrinus a n d Little Terns Sterna albifrons) did not show particular preferences at this level . With regard to nest site characteristics of each species, they were often different from random points and, less frequently, from those of the other species. Yellow-legged Gulls preferred sites with less sand, higher vegetation cover and taller plants; the opposite was true for Kentish Plovers. Intermediate characteristics were selected by Oystercatchers and Little Terns. Significant associations were found between Oystercatchers and Yellow-legged Gulls, Oystercatchers and Kentish Plovers, Kentish Plovers and Little Terns. Our study suggests that physical factors (i.e. nest site features) and behavioral factors (association resulting in better protection from predators, or due to a limited feeding overlap in the nearby intertidal areas) interact in the habitat selection of the four species studied in the Po Delta. The observed association between oystercatchers and gulls deserves further research.