Seasonal dietary differences of the Yellow-footed Gull (Charadriiformes: Laridae) in Isla Partida Norte, Gulf of California, Mexico

Abstract

The Yellow-footed Gull (Larus livens) is one of the few members of the genus Larus inhabiting the Gulf of California. Its breeding biology, nest phenology, and behavior have been long studied but little is known about seasonal changes in its diet. In this study, we tested if the diet of Yellow-footed Gull differed between reproductive (April and July) and non-reproductive (December). The frequency of occurrence of food items in gull's pellets and food niche breadth (FNB) and Levin's diversity (Best) indexes for each sampling period (April, July, and December), as well as Pianka's dietary overlap (O%) and Morisita's (MI) dietary similarity indices between periods were estimated. We identified 9 taxa classes, whose frequency of occurrence varied significantly between all comparisons (April and December, July and December, April and July), and between reproductive (April-July) and non-reproductive seasons. FNB and Best diversity indexes indicated that Yellow-footed Gull has a broader niche spectrum during the breeding season (April-July), while dietary overlap estimators (O% and MI) were higher between July vs. December and April vs. December, but lower in April vs. July. Results are contrasted with previous studies of gull's feeding ecology, and possible effects of local human activity are discussed.