Social foraging European shags: GPS tracking reveals birds from neighbouring colonies have shared foraging grounds

Developments in tracking technologies have enhanced our understanding of the behaviours of many seabird species. However few studies have examined the social aspects of seabird foraging behaviour, despite the effect this might have on the distribution of foraging areas and the differences that might arise between colonies. Here we use bird-borne GPS and behavioural observation to study the social foraging behaviour and habitat use of breeding shags from three breeding colonies in the Isles of Scilly, UK. Thirteen breeding shags from three colonies (six at two colonies and a single bird from another) were tracked between 2010 and 2012 and related to observations of conspecific foraging aggregations (2013-2014). Tracked shags had short foraging ranges (1.74 ± 1.6 km) mostly travelling to shallow waters between the islands and observations revealed that many shags foraged in large social groups that were consistent in time and space. There were also no clear differences in foraging distributions among colonies—birds shared similar foraging grounds. Our finding provides important insight into the use of social information among foraging seabirds and how this may lead to shared foraging areas, as well as space partitioning.