Publication Date

Spring 2016

Degree Type


Degree Name

Master of Science (MS)


Biological Sciences


Scott A. Shaffer


California Current, Diet, Larus, Refuse, Urban, Western Gull

Subject Areas

Biology; Ecology; Wildlife conservation


As human populations expand, they force free-ranging animals to adapt to an increasingly urban environment, resulting in changes in diets, reproductive success, and mortality. The diets of two western gull (Larus occidentalis) breeding populations in central California were compared. One colony, Año Nuevo Island (ANI), is 1 km from shore and within 30 km of a municipal landfill. The other colony, Southeast Farallon Island (SEFI), is located 45 km off the shore of San Francisco, CA. Given the proximity of ANI to the shore and the landfill, I predicted that gulls from ANI would have more garbage in their diets. Indeed, gulls from ANI consumed over three times more garbage. Twenty-three percent of wet diets from gulls at ANI contained garbage, whereas garbage made up only 6% of wet diets from gulls at SEFI. Despite the appearance of garbage in gull diets, birds from both colonies consumed a range of marine prey, and Clupeiformes, Euphausiacea, and Gadiformes were important to both colonies. Isotopic values (15N and 13C) measured in gull feathers were similar between colonies, suggesting that gulls from both populations consume similar prey from the marine environment during the non-breeding phase. The reliance on stable, easily accessible food from landfills during the breeding season may be an important adaptation for western gulls to cope with urbanization and declines in prey species in the California Current during the energy-intensive chick-rearing period