A comparison of foraging at refuse tips by three species of gull (Laridae)

The comparative foraging of Black‐headed (Larus ridibundus), Herring (L. argentalus) and Great black‐backed gulls (L. marinus) was investigated at refuse tips in north‐east England. Between October and February, two races of Herring gulls are present, those which breed in Britain (L. a. argenteus) and the larger Scandinavian herring gulls (L. a. argentatus). Three types of feeding at a refuse tip were distinguished: undisturbed primary feeding (highly competitive feeding on freshly dumped rubbish), disturbed primary feeding (agile surface dipping for food from the air, close to the working bulldozer) and secondary feeding (low density feeding on dispersed and partially buried rubbish). In undisturbed feeding the largest individuals (i.e. Great black‐backed gulls) were competitively superior and achieved the highest feeding success. The smallest individuals (i.e. Black‐headed gulls) were rapidly excluded by the larger gulls. Scandinavian herring gulls were competitively superior in intraspecific interactions, but they were selectively attacked by Great black‐backed gulls. Disturbed feeding, in contrast, was used most by Black‐headed gulls and not at all by Great black‐backed gulls. Large body size is a disadvantage in disturbed feeding, due to increased wing loading acting as a constraint on manoeuvrability. Overall, the separation between species, in terms of the proportion of food gained by different feeding methods, was estimated at 30–50%. Cold and windy conditions led to increased numbers of Herring and Great black‐backed gulls at tips, and numbers of Great black‐backed gulls were also higher when fish landings at the coast were low. There were significant differences between tips in the number of Great black‐backed and Black‐headed gulls, possibly due to differences in working regime which influence the feeding opportunities which were available.