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

As many as 6000 Silver Gulls (Larus novaehollandiae) per hour were recorded leaving a landfill near Wollongong, Australia during the breeding 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 breeding colony 12 km away. Gulls visited the depot on approximately half the number of days monitored. Within a day, most individuals (62% of marked birds observed) visited the depot only once, although some individuals 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 two breeding seasons, 85% of regurgitations from Silver Gulls trapped at nests contained only human refuse, 13% only natural food, and 2% a mixture of both. Meat comprised 63% of the human refuse and the rest consisted of a variety of other (mainly starchy) items. The data suggest either that gulls gorged themselves quickly at the landfill site or that 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, paralleling changes in the number of young chicks in the colony and the density of the breeding population. The highest proportion of natural food in regurgitates was consistently recorded early in the breeding season (September) when the first eggs of the season had hatched. These early eggs produced most of the fledged chicks for the breeding season.