Inter-colony variation in the foraging behaviour and resource selection of breeding Herring Gulls Larus argentatus

The resources available to breeding seabirds within their foraging ranges can influence productivity, either directly through the quality and quantity of food consumed by chicks, or indirectly by affecting the foraging behaviour and efficiency of parent birds. Where local resource availability is low, or the quality of resources are poor, species with flexible time-energy budgets can increase their foraging effort to provide adequate energy and nutrients to their chicks, although this may come at the expense of nest attendance. We investigated provisioning rates and nest attendance in European Herring Gulls Larus argentatus from seven colonies across southwest Scotland and Northern Ireland during two chick-rearing periods (2013 and 2014) in relation to the food resources used by these colonies. We observed variation in provisioning rates and nest attendance between colonies, and variation between years in nest attendance. We found no significant relationships between these behaviours and the proportion of intertidal prey consumed, suggesting that provisioning rate and nest attendance did not differ between resource types at the colony level. We also found no evidence that variation in behaviours was related to breeding success. Our results suggest that, within this region, the type of resources consumed had a greater influence on Herring Gull breeding success than differences in two proxies of foraging efficiency (provisioning rate and nest attendance), although other factors may also have influenced breeding success. Our work highlights the benefit of determining what food resources are provided to chicks, in addition to measuring foraging behaviours, to fully understand the consequences of consuming different resources on the breeding success of generalist foragers.