Average clutch size for large Larus gulls is close to three eggs, and the production of a clutch of four is uncommon (Keith 1966; Paludan 1951; Vermeer 1963). We report here on a colony of Western Gulls (Larms occidentalis) in which many clutches containing four and five eggs were found. It is of particular interest that in these large clutches not only was hatching success low but also eggshell thickness was reduced.

With the study of the equilibrium theory of island biogeography pioneered by MacArthur and Wilson ( 1963, 1967), increasing attention has been paid to the study of turnover rates (Mayr 1965; Diamond 1969, 1971; Power 1972; Terborgh and Faaberg 1973). The failure of bird species turnover rates to show the predicted negative correlation with island size in the California Channel Islands (Diamond 1969) raises questions as to what factors other than island size may be involved in determining species turnover. · Previous studies of avifaunal turnover have treated faunas as a whole and have not differentiated turnover rates for rare species from those of common species. Since very large birds and species at high levels on the food chain often exist at relatively low densities, these organisms would be expected to have a greater probability of extinction on small islands than those species which maintain larger populations (Brown 1971). A theoretical basis for this hypothesis can be derived from Gilpin ( 197 4). He has shown ( pers. comm.) that extinction rates should be a negative exponential function of K, and thus should be very sensitive to small population size.

GULLS (Family Laridae) are generalized foragers that utilize many kinds of food items ranging in size from insects to the carcasses of whales. They forage in the air, on foot in fields and the intertidal zone, and by swimming and diving for underwater prey. Although species and individual gulls may show considerable specialization in foraging techniques and food preferences, most species of gulls forage at least occasionally over a large range of available habitats and use a wide variety of feeding techniques.