Predator-prey interactions between great black-backed gulls (Larus marinus) and puffins (Fratercula arctica L.), and the evolutionary significance of puffin grouping behaviour

Abstract

The alms of this study were to quantify various aspects of predator-prey interactions between Great Black Backed Gulls (Larus marinus) and Common Puffins (Frateroula arotica Le) in order to assess the possible long term effects of predation by gulls on a single Puffin colony and to examine the possible influence of avian predators on Puffin social behaviour. Kiore has been little quantification of the extent of Great Black-Backed Gull predation of Puffins throughout the gull breeding season. Chapter One extends data already published on gull predation of Puffins on the island of Dun, St Kilda, by showing what proportion of gall diet comprised Puffins and by indicating the importance of Puffin prey to gull breading success. Chapter Two describes the ranging behaviour and hunting success of gulls on Dun. Gulls only hunted flying Puffins and concentrated their hunting efforts in areas near, but not directly over, their own nests. Any one pair of gulls shared on average about one third of its hunting range with two or three other pairs of Gulls attempted to catch Puffins most often in areas where Puffins, flying in polarised flocks termed 'wheels', habitually turned in to fly over land or out to fly over the sea. With increasing numbers of Puffins in a wheel, gulls made fewer attempts to catch Puffins and took longer to make a successful kill. The grouping behaviour of Puffins is one of the most striking features of the species' social life at the breeding colony. Chapter Three describes and quantifies temporal and spatial aspects of Puffin grouping behaviour at a. variety of colonies. Differences in the diurnal phasing of the formation of different types of Puffin groups and Abstract (cont.) regularities in the spatial distribution of groups in the sea and in the air indicate that individual Puffins regularly synchronised some of their movements in and around the breeding colony with numbers of other Puffins breeding in or using the same part of the colony. The flight behaviour of an individual Puffin in a wheel flock above a sub-colony was influenced by the number of other Puffins in the wheel, b-wind speed and direction, and by the presence of a hunting gull in the vicinity of the wheel. To conclude, the implications of the present study for the management, monitoring and future study of Great Black-Backed Gulls and Puffins are outlined.