The spatial structure of seabird distributions. R.A. Robinson 1,2 , J.B. Reid 1 & M.C. Bailey 3 . 1 Joint Nature Conservation Committee, 7 Thistle Place, Aberdeen, AB10 1UZ, U.K. 2 British Trust for Ornithology, The Nunnery, Thetford, Norfolk, IP24 2PU, U.K. e.mail: rob.robinson@bto.org 3 FRS Marine Laboratory, Victoria Road, Aberdeen, AB11 9DB, U.K. Abstract The distribution of seabirds at sea during the breeding season is likely to be determined by a number of factors, including colony location and the dispersion of food resources. We characterise the distribution of three species: Northern Fulmars Fulmarus glacialis, Northern Gannets Morus bassanus and Common Guillemots Uria aalge foraging in northern Scottish waters, using patterns of autocorrelation to assess the importance and scale dependency of food dispersion and the location of breeding colonies. We show that patterns of seabird dispersion during the breeding season were determined hierarchically, with colony location determining broad scale patterns and food resources finer-scale patterning of dispersion. Introduction The importance of scale in determining patterns in ecology and the spatial and temporal processes underlying them is increasingly being recognised (Wiens 1989; Caldow & Racey 2000) and has generally received greatest attention in marine systems, where there tend to be fewer obviously discrete habitat boundaries (Stommel 1963; Denman 1994). Foraging seabirds exhibit extremely aggregated dispersion patterns, which vary according to the scale at which they are characterised (Hunt & Schneider 1987). For example, during the breeding season, many birds are likely to be constrained by their need to return to the breeding colony, which will limit foraging distances (e.g. Wanless et al. 1997). Birds might also be expected to distribute in relation to the occurrence of their prey. Previous studies have mostly concentrated on auks foraging near discrete oceanographic structures, such as thermal fronts (Schneider & Piatt 1986; Hunt & Schneider 1987; Mehlum et al. 1999). However, in areas away from such structures, birds are more dispersed requiring studies of greater extent. In this paper, we characterise the spatial distribution at sea of three species of seabird, Northern Fulmar Fulmarus glacialis, Northern Gannet Morus bassanus and Common Guillemot Uria aalge, which have different foraging strategies. Fulmars feed on a variety of fish and zooplankton, largely by surface-seizing, although they frequently congregate around trawlers to feed on fisheries waste. Gannets search and feed from the air, often in large numbers, plunge-diving on shoals of fish, although they also attend trawlers. Guillemots rarely feed at trawlers and mostly dive from the surface, pursuit-diving for sandeels 1