| Summary: | Nest-site selection by tropical Roseate Terns (Sterna dougallii) was examined on Aride Island, Seychelles. Continuous variables reflecting concealment of the nest site, shelter, vegetation cover and intraspecific nest density were measured for nest-sites and random points. Seasonal variation in the initiation of nests with overhangs and their influence on hatching success and adult intraspecific aggression towards chicks were also examined. Roseate Terns selected nest-sites closer to taller vertical objects, and with a higher percentage of rocks, logs or branches overhanging the nest than occurred at random points. Nest-sites in small colonies differed more from the available habitat than did those in the main colony. Nesting density was positively correlated with the amount of rock cover. On Aride and other colonies in the tropics Roseate Terns breed at higher densities than their temperate counter-parts and spacing between neighbors may be a main factor in the selection of nest-sites, especially for birds nesting at the peak of the breeding season. Nest-site characteristics, notably overhangs, had no influence on hatching success. However, the proportion of chicks that died from adult pecking was significantly lower in nests with overhangs. Concealment is a main factor of Roseate Tern nest-site selection throughout its breeding range, in both tropical and temperate areas, but the factors selecting for concealment seem to vary amongst colonies. On Aride concealment appeared to be advantageous in defending territories and protecting young chicks from attacks of adults. Artificial overhangs could be provided to enhance chick survival.
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