Breeding Ecology of the Swallow-Tailed Gull, Creagrus furcatus

Abstract

THE Galfipagos Swallow-tailed Gull, Creagrus furcatus-referred to as Creagrus throughout this paper-was little known until a series of papers by Moynihan (1962), Hailman (1964a, 1964b, 1965), Snow and Snow (1967, 1968), and Nelson (1968a) showed it to be one of the most aberrant and interesting species of gulls. Hailman (1964b) showed that the species breeds throughout the year but that natural groupings of nests have their breeding synchronized, probably by social stimulation. Snow and Snow (1967), working on South' Plaza Island, found that individual pairs of gulls lay, on average, every 10 months if successful in raising a young, and rather more frequently if unsuccessful. Between cycles the molting adults are absent from the colonies for an average of about 4.5 months. With the exception of the Snows, who made fortnightly observations between February 1963 and April 1964, observers of the species had spent little time in Gal•pagos and a further long-term study on the species was obviously needed.