Nestling growth and nest success of Gull-billed TernGelochelidon nilotica(Aves: Sternidae) in western Iran

Abstract

The nesting success and nestling growth were studied in a Gull-billed Tern Gelochelidon nilotica Gmelin, 1789 colony located in western Iran, during the 2008 breeding season. The nesting success was modelled in order to assess the effects of various nest-site parameters and nest initiation date. Nestling growth rate, described as body mass, head-bill and tarsus growth per day during the first 10 days of age, was analyzed in relation to brood size and the hatching position of nestlings. Mean daily growth rate of nestlings' mass (7.82 ± 0.35 g/day) varied in broods of different size but remained independent of nestlings' hatch order within the brood. Similarly, the growth rate of head-bill length was influenced only by brood size while neither brood size nor hatching position had a significant effect on the wing length growth rate. Nest initiation dates and plant cover around the nests were the most important factors predicting nesting success. As time of breeding period progressed, the rate of nesting success increased. Higher plant cover around the nest also increased the nesting success, probably by hiding the eggs and providing shelter for nestlings thus decreasing predation and mortality rate.