Comparative Feeding Behavior of Immature and Adult Herring Gulls
نویسنده
چکیده
Many birds do not breed until they are 2 or more years old. Such delayed breeding is generally found among large, long-lived, non-passerine species. Lack (1954) suggested that delayed breeding has probably evolved in species in which reproduction at an earlier age would not be likely to succeed or might be harmful to the parents. Ashmole (1963) and Amadon (1964) suggested that young birds might be unable to catch food as efficiently as adults do. Recently, a number of field studies have shown that the ability to obtain food improves with age (see Buckley and Buckley 1974 for references) . Given the inefficiency, it might be expected that the young have to compensate somehow for their lack of success, e.g. by spending more time in feeding. The object of this study was first to establish feeding efficiency in young and adult Herring Gulls (Larus argentatus), which show delayed breeding, and then to see how the young make up for any inefficiencies. The study was made on Walney Island, Cumbria, England, in 1973 and 1974. Herring Gulls and Lesser Black-backed Gulls (L. ~USCUS) breed on the southern end of the island. The colony is very dependent on nearby food sources such as the large intertidal areas of Morecambe Bay and a garbage dump on the island.
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