Nesting success of White Terns and White-tailed Tropicbirds on Cousine Island, Seychelles

Abstract

This study investigates the breeding success of two tropical seabirds that exploit dissimilar nesting habitats on Cousine Island in the Seychelles  archipelago, the White Tern Gygis alba and the White-tailed Tropicbird Phaethon lepturus, which nest  in trees and in crevices on the ground, respectively. Both species have a clutch of one  egg. Over a 23-month study period, the outcomes of 134 nesting attempts by White Terns and 285 by White-tailed Tropicbirds were followed. White Terns produced an average of 0.4 chicks per attempt, significantly more than that of White-tailed Tropicbirds (0.25). Hatching success did not differ between the two species, but fledging success of White Terns (62%) was significantly higher than that of White-tailed Tropicbirds (43%). Nesting success of White-tailed Tropicbirds may be less successful than White Terns because their ground nests are at risk to purely terrestrial predators, in addition to predators that are both terrestrial and arboreal. Many nests of White-tailed Tropicbirds failed during the first two weeks of the incubation and nestling periods, but the reasons for this are unclear. Food availability may influence the reproductive success of both species.

OSTRICH 2009, 80(2): 81–84