Most studies of the kleptoparasitic behavior of gulls have involved intermediate-sized species. This study examined the kleptoparasitic relationships between the Pied Oystercatcher (Haematopus longirostris) feeding on Surf Clams (Mactra rufescens) and a large gull species, the Pacific Gull (Larus pacificus) in the swash zone of an ocean beach in Tasmania, Australia. Oystercatchers caught Surf Clams buried in sand using visual cues when the clams were covered by shallow water at low tide. There was no selection for clam size, possibly because they were unable to assess size before capture. Shells were not broken by hammering, but by forcing the bill into and between the valves. Handling time was prolonged and was significantly related to shell length. The profitability of clams (ash-free dry mass of flesh ingested per second of handling time) was independent of shell length. Pacific Gulls stole 8% of all clams taken by the oystercatchers. The mean length and ash-free dry mass of clams stolen (54.3 ± 0.64 mm; 8.14 ± 1.5 mg, N = 51) were significantly greater than that of all clams (46.8 ± 0.65 mm; 5.10 ± 0.3 mg, N = 98) caught by the oystercatchers. The oystercatchers had frequent rest periods between bouts of foraging, suggesting they were able to capture and ingest clams faster than they could digest them and experienced a digestive bottleneck. Losses to Pacific Gulls probably had no significant effect on the oystercatchers as they had adequate feeding time available to compensate.
|Number of pages||6|
|Publication status||Published - 2005|