title: Changes in behaviour drive inter-annual variability in the at-sea distribution of northern gannets.
abstract: The at-sea distribution of seabirds primarily depends on the distance from their breeding colony, and the abundance, distribution and predictability of their prey, which are subject to strong spatial and temporal variation. Many seabirds have developed flexible foraging strategies to deal with this variation, such as increasing their foraging effort or switching to more predictable, less energy dense, prey, in poor conditions. These responses may vary both within and between individuals, and understanding this variability is vital to predict the population-level impacts of spatially explicit environmental disturbances, such as offshore windfarms. We conducted a multi-year tracking study in order to investigate the inter-annual variation in the foraging behaviour and location of a population of northern gannets breeding on Alderney in the English Channel. To do so, we investigated the link between individual-level behaviour and population-level behaviour. We found that a sample of gannets tracked in 2015 had longer trip durations, travelled further from the colony and had larger core foraging areas and home range areas than gannets tracked in previous years. This inter-annual variation may be associated with oceanographic conditions indexed by the North Atlantic Oscillation (NAO). Our findings suggest that this inter-annual variation was driven by individuals visiting larger areas in all of their trips rather than individuals diversifying to visit more, distinct areas. These findings suggest that, for gannets at least, if prey becomes less abundant or more widely distributed, more individuals may be required to forage further from the colony, thus increasing their likelihood of encountering pressures from spatially explicit anthropogenic disturbances.
authors.affiliation: School of Environmental Sciences, University of Liverpool, Liverpool, L69 3GP UK.
authors.forename: V
authors.initials: V
authors.lastname: Warwick-Evans
authors.affiliation: British Trust for Ornithology, The Nunnery, Thetford, Norfolk, IP24 2PU UK.
authors.forename: P W
authors.initials: PW
authors.lastname: Atkinson
authors.affiliation: School of Life and Environmental Sciences (Burwood Campus), Deakin University, Geelong, VIC Australia.
authors.forename: J P Y
authors.initials: JP
authors.lastname: Arnould
authors.affiliation: Alderney Wildlife Trust, St Annes, GY9 3TA Alderney, Channel Islands.
authors.forename: R
authors.initials: R
authors.lastname: Gauvain
authors.affiliation: Department of Life Sciences, University of Roehampton, Whitelands Campus, London, SW15 5PU UK.
authors.forename: L
authors.initials: L
authors.lastname: Soanes
authors.affiliation: School of Environmental Sciences, University of Liverpool, Liverpool, L69 3GP UK.
authors.forename: L A
authors.initials: LA
authors.lastname: Robinson
authors.affiliation: School of Environmental Sciences, University of Liverpool, Liverpool, L69 3GP UK.
authors.forename: J A
authors.initials: JA
authors.lastname: Green