Colony attendance of common guillemots during the non-breeding season

Abstract

**Abstract:** Competition for high quality breeding sites in colonial seabird species is often intense, such that individuals may invest considerable time in site occupancy even outside of the breeding season. The site defence hypothesis predicts that site occupancy should be positively correlated with breeding phenology and success such that more successful sites are occupied earlier and/or more frequently. However, few studies have related non-breeding season attendance and subsequent breeding performance. Therefore, our understanding of the potential life-history benefits of this behaviour are limited. To address this, we used time-lapse photography to record the non-breeding attendance of >80 pairs of common guillemots, Uria aalge, breeding on the Isle of May, Scotland. Images were taken of sites every 15 minutes for three non-breeding seasons (start of October to end of March). We then recorded the time spent at each site, each day, each non-breeding season. We then followed breeding phenology and success at each site in the subsequent breeding season. Attendance at sites began in late October with sites gradually be attended more frequently and for longer until almost all sites were occupied for all daylight hours just prior to the breeding season (end March). We found that higher quality sites were occupied earlier and more often. Sites occupied more often had significantly earlier lay dates, and those occupied earlier were more successful, supporting the site defence hypothesis. These clear effects of non-breeding attendance on breeding timing and success highlight the potential fitness benefits of this behaviour on key life-history processes such a breeding. **Authors:** Sophie Bennett¹, Mike Harris¹, Sarah Wanless¹, Jonathan Green², Mark Newell¹, Kate Searle¹, Francis Daunt¹ ¹UK Centre for Ecology & Hydrology, ²University of Liverpool