Results from the first GPS tracking of roof-nesting Herring Gulls Larus argentatus in the UK

Abstract

ABSTRACT Recent developments in GPS tracking technology allow the movements of bird species to be followed in ever-greater detail. Seabird research is benefiting greatly, due to the challenges of tracking species that often roam widely out at sea. Amongst the gulls, one of the pressing issues is to understand the ecology of the relatively recent urban colonists and how they differ from their counterparts in traditional rural colonies. Here, we present what we believe are the first GPS results from roof-nesting gulls. Four adult Herring Gulls (two males, two females) were fitted with GPS tags in May 2014 in the seaside town of St Ives, Cornwall (breeding colony c 250 pairs), and tracked for c 100 days during the 2014 breeding season. We estimated the home ranges of the four individuals and how their movement behaviour varied through the 24-h period and across the breeding season. The results highlight how variable movement behaviour was among individuals: whilst one bird roamed widely (90% range estimate = 560 km2), heading >50 km offshore and often active at night or roosting at sea, two birds had small ranges (<10 km2), always attended the colony at night and rarely headed more than a few hundred metres offshore, with the fourth displaying intermediate behaviour. All of the birds regularly utilised a few key sites within the agricultural landscape south of St Ives. Whilst this study was too small to allow general conclusions to be drawn about urban Herring Gulls, it reinforces how variable individual behaviour can be amongst the large gulls and will be particularly interesting when applied to a larger sample of birds, especially in big urban gull colonies further inland.