Seasonal patterns in numbers of Kelp Gulls <i>Larus dominicanus vetula</i> in the Port Elizabeth area and on Bird Island, Algoa Bay

Abstract

Numbers of Kelp Gulls recorded within the Port Elizabeth area peaked in the austral autumn, and on average comprised approximately 4% of the southern African population. Between 66% and 80% of Kelp Gulls recorded around Port Elizabeth were in adult plumage. It is assumed that adults breeding outside of the Port Elizabeth area move into the area after breeding. During their first year Kelp Gulls showed distinct periods of influx — thought to be due to the fledging of local birds — followed by a movement of birds into the region from further west. Birds are thought to be attracted to the urban environment by sources of human-provided foodstuffs available at the harbour and at a municipal rubbish tip. Seasonal patterns differed across sites in the Port Elizabeth area and were rarely the same for all age categories at any one site. Numbers of birds at roosts did not appear to be correlated to the state of the tide, but numbers foraging on the Swartkops estuary were. Numbers of adult Kelp Gulls at Bird Island peaked during the breeding season. Juvenile birds left the island soon after fledging.

Ostrich 2006, 77(3&4): 195–201