Monitoring gull populations and diets: indicators of ecosystem health
Gulls are among the most conspicuous and abundant seabirds in Atlantic Canada, yet we know surprisingly little about their diets, movements and migrations. Populations of Herring Gulls were on the rise for much of the 20th century once they were protected under the Migratory Bird Act. Yet in recent decades, population declines have been observed throughout much of the Maritimes, reasons for which are unknown. However, the most recent census by the GMWSRS in 2001 found Grand
Manan populations to be on the rise: nearly 12,000 pairs of Herring Gulls and just over 600 pairs of Great Black-backed Gulls were nesting
in the Grand Manan archipelago. We are studying the diets
and movements of gulls in the lower Bay of Fundy which can provide insight into factors that might be influencing population trends. Dietary studies discovered a mixed diet of primarily of crabs, fish, and krill, but also smaller quantities of other seabirds such as eider ducklings and storm-petrels. Bio-chemical analysis of bird blood and feathers revealed Great Black-backed Gulls to be feeding at a higher trophic level, i.e. higher up the food chain, than Herring Gulls. Satellite tags were deployed on three Herring Gulls and tracked migrations from Fundy to wintering areas in the Chesapeake Bay, USA. One gull has been tracked for more than 900 days.
Herring Gulls are widespread throughout much of Canada, nesting in every province and territory from the Great Lakes to the Arctic Circle. Future studies will be collaborating with research projects elsewhere to compare the foraging ecology and migration dynamics of this species across a wide range of habitats.