Prey consumed by breeding Pacific Gulls (Larus pacificus) were identified and quantified on seven islands in the Furneaux Group, Bass Strait, Australia, over the 2003/04 austral summer to examine temporal and spatial variation in dietary preference. Non-invasive dietary sampling involved collection of non-consumed parts of prey (large particles) and regurgitated pellets of prey remains (pellets) from feeding platforms every two weeks. Of the128 prey items identified, 17 of these items were prominent in the diet of Pacific Gulls. Of these, seven were identified by both large particles and pellets of prey remains, three only as large particles and the remaining seven only in pellets. PRIMER multidimensional scaling revealed differences between stages of breeding and between sites in the abundance of each type of prey found as large particles, but only between sites for prey found in pellets. Based on the relationship between body mass and dietary requirements a breeding adult Pacific Gull requires, on average, 600 kJ/d over the breeding season. This study identified prey corresponding to only 193 ± 35 kJ/d which equates to a total biomass of approximately 1,000 kg of prey being consumed by the 108 breeding Pacific Gulls, or 19 kg per breeding pair. Results were biased toward hard-bodied prey, and hence, this research failed to identify 90% of the food consumed by the Pacific Gull population. Caution is advised against one-off sampling in time and space, and using simple techniques, to examine dietary preference in gulls.
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Vol. 31 • No. 4