Spatio‐temporal differences in the diet and trophic ecology of Kelp Gulls (Larus dominicanus) in South Africa

Abstract

Opportunistic species, including some gulls (Laridae), can benefit from urbanization and increased anthropogenic food resources. Knowledge of the level of exploitation of anthropogenic resources by gulls is crucial to understand how changes in food availability might affect their populations, which in turn may impact other species. The Kelp Gull Larus dominicanus is widely distributed in the southern hemisphere and consumes a wide variety of resources, from waste in landfills to seabirds. We assessed if proximity to landfills influenced the diet and trophic ecology of Kelp Gull incubating adults and chicks using a combination of conventional diet sampling (stomach contents, regurgitated pellets), and carbon and nitrogen stable isotope analysis of blood plasma in seven colonies over two consecutive years in South Africa. Kelp Gulls consumed a variety of resources, including marine (e.g. fish), coastal (e.g. molluscs), terrestrial natural (e.g. insects, mammals), or terrestrial anthropogenic (e.g. chicken, bread) items. Inter‐annual differences were most apparent among gulls breeding next to a seabird colony, whereas gulls breeding at other colonies were more consistent in diet and trophic ecology. At most colonies, chicks were fed more natural and higher trophic level food items than were consumed by incubating adults. Overall, distance to landfill did not strongly affect the diet and trophic ecology and our results suggest that the Kelp Gull's broad feeding ecology allows it to buffer changes in food availability by switching among food resources. However, such dietary changes triggered by human actions may impact other species, including threatened seabirds.