FOOD AND FEEDING ECOLOGY OF BREEDING SILVER GULLS (LARUS-NOVAEHOLLANDIAE) IN URBAN AUSTRALIA

As many as 6000 Silver Gulls (Larus novaehollandiae) per hour were rec orded leaving a landfill near Wollongong, Australia during the breedin g season. The numbers of gulls that entered and left this site varied seasonally, with a minimum recorded in the non-breeding season. In two breeding seasons, from September 1988 to January 1991, 74% and 62% of wing-tagged, breeding gulls visited the landfill from an island breed ing colony 12 km away. Gulls visited the depot on approximately half t he number of days monitored. Within a day, most individuals (62% of ma rked birds observed) visited the depot only once, although some indivi duals visited up to four times. The average duration of visits was 1 h . These data suggest a high turnover of gulls at the landfill. Over tw o breeding seasons, 85% of regurgitations from Silver Gulls trapped at nests contained only human refuse, 13% only natural food, and 2% a mi xture of both. Meat comprised 63% of the human refuse and the rest con sisted of a variety of other (mainly starchy) items. The data suggest either that gulls gorged themselves quickly at the landfill site or th at a considerable amount of refuse was obtained away from the landfill site under investigation. The proportion of the population feeding on natural food changed from 5% to 25% through the breeding season, para lleling changes in the number of young chicks in the colony and the de nsity of the breeding population. The highest proportion of natural fo od in regurgitates was consistently recorded early in the breeding sea son (September) when the first eggs of the season had hatched. These e arly eggs produced most of the fledged chicks for the breeding season.