A century of change in Glaucous-winged Gull (Larus glaucescens) populations in a dynamic coastal environment

Abstract

ABSTRACT As conspicuous midtrophic omnivores, gulls can serve as useful indicators to characterize long-term ecological changes in marine ecosystems. Glaucous-winged Gulls (Larus glaucescens) have been studied in the Georgia Basin of British Columbia, Canada, an urbanized coastal zone, since the late 1800s. We collated all available information to develop a (noncontinuous) 111-year time series of counts at breeding colonies, and combined these counts with demographic vital rates to assess how changes in historical gull egg harvesting practices, forage fish abundance, and Bald Eagle (Haliaeetus leucocephalus) numbers affected gull population trajectories from 1900 to 2010. Mean counts at 87 breeding colonies in the Georgia Basin showed a nonlinear trend, increasing from historical low counts in the early part of the twentieth century to peak values in the 1980s, and declining thereafter to the end of the time series. Demographic models that integrated temporal trends in clutch size and nesting success, and...