Population change among Pacific, kelp and silver gulls using natural and artificial feeding sites in south-eastern Tasmania

Abstract

The kelp gull, Larus dominicanus, which is widely distributed around the southern hemisphere, has become established in Australia only in the past half-century. The greatest numbers of kelp gulls in Australia are now found in south-eastern Tasmania in sympatry with the two endemic species, the morphologically similar Pacific gull, L. pacificus, and the smaller silver gull, L. novaehollandiae. We examined populations of the three species in this area. We surveyed large refuse tips and specific shoreline sites in the Hobart area regularly during the winter months in 1981 and again in 1992, recording numbers of each species, and age classes of kelp and Pacific gulls. Between the two survey periods, the number of Pacific gulls and the total number of all gulls present at refuse tips remained unchanged. There was, however, a marked increase in the number of kelp gulls at tips, equivalent to an annual rate of increase of 22.8%, and a corresponding decrease in the number of silver gulls. Kelp gulls of all ages were over-represented at refuse tips, while adult Pacific gulls fed preferentially at more natural shoreline sites. At shoreline sites, adult Pacific gulls appeared to exclude kelp gulls from small bays in 1981, but kelp gulls were present in most of these bays eleven years later. Reducing access to food at refuse tips may be an effective means of controlling the kelp gull population in this area.