Diets of nestling gull-billed terns in coastal Virginia

We studied the diets of nestling Gull-billed Terns (Sterna nilotica) at col onies in coastal Virginia during the breeding seasons of 1995 and 1996 as p art of a long-term study of the species. No previous quantitative assessmen ts had been made of diets of this species anywhere along the Atlantic Coast , and only a few observations had been reported from other coastal areas in the southern United States. during 80 h of observations over the two seaso ns, 757 feeding observations were made, primarily at two colony sites. We e xamined how prey type (fish, marine invertebrates, terrestrial prey) and si ze were influenced by year, tide cycle, season (early and late) and age of the young (small chicks <7 d old versus large chicks >7d). We did not find significant year differences, but all other factors revealed statistically significant results. Older (>7d) chicks were fed relatively more terrestria l and marine invertebrate prey than were younger chicks. In June (early sea son), fewer fish and terrestrial prey were fed to chicks than later (July-A ugust). Most prey were less than one bill length in size, with the majority of the smallest prey being marine invertebrates. Tide cycle influenced pre y delivered with terrestrial prey becoming relatively more important during high and ebb periods than during low and flood tides when aquatic prey dom inated. the major marine invertebrate prey taken was the fiddler crab (Uca spp.). Terrestrial prey consisted mostly of large odonates and orthopterans . Unlike earlier reports from Europe, we found no regurgitated food pellets in any of the colonies in either year. This study confirms that the Gull-b illed Tern is an extremely opportunistic feeder and has adapted to a variet y of habitats, helping to explain its cosmopolitan distribution.