SEA BIRDS FEEDING BEHAVIOUR

Foraging and feeding behavior of seabirds

Abstract

The European Seabirds at Sea (ESAS) database was established in the early 1980s using a common format. It contains the results of ship-based and aerial seabird surveys in the Northwest European waters, collected using standard methods. The emphasis has always been on mapping distribution patterns and variations in relative abundance, from which seabird abundance estimates for certain sea areas could be made. The data have been used first to evaluate different sea areas in terms of their vulnerability for surface pollutants. Later studies put more emphasis on ecological aspects underlying seabird distribution and from this work a growing need for more adequate, but still standardised, coding of behaviour types emerged. In this manual, a coding system is introduced that allows specific coding of associations of birds and marine mammals with certain surface phenomena (including land), coding of multi-species feeding associations (feeding flocks) and coding of a variety of behaviour types, with emphasis on feeding behaviour and foraging interactions. In this coding method, the original aim and style of data collecting of seabirds at sea remains intact, and new data are therefore directly comparable with historical material. The coding is thought to be of interest for ESAS participants as well as other groups studying the behaviour of seabirds at sea.

Foraging and feeding behavior of seabirds

Introduction

During most of the 20th century, seabirds at sea were studied only occasionally and as a matter of opportunity (Jespersen 1930; Bierman & Voous 1950). Particularly since the late 1970s, however, systematic aerial and shipboard seabird surveys have been conducted in many parts of the world. Bailey & Bourne (1972) stressed the need for uniformity of counting methods, to ensure that observations made by different observers and in different sea-areas are comparable. Although global standardisation of methods has never been achieved, despite serious attempts and comparisons of different methods, regional standardisation has been a major step forward in obtaining consistent and comparable results (Brown et al. 1975; Tasker et al. 1984; Van Franeker 1994; White et al. 1999).

In north-west European waters, the establishment of the European Seabirds At Sea (ESAS) database, in which a number of institutes from countries around the North Sea store data in a common format following recommendations of standard recording techniques (Tasker et al. 1984), has been a particularly fruitful example of standardisation, subsequent co-operation and data collection (Tasker et al. 1987; Webb et al. 1990; Camphuysen & Leopold 1994; Skov et al. 1995; Stone et al. 1995; Offringa et al. 1995; Garthe et al. 2003).

Discussion

In Europe, many of these surveys were designed to collect basic information on distribution and relative abundance of seabirds at sea (Tasker et al. 1984; Komdeur et al. 1992), often following the desire to categorise different sea areas in terms of their vulnerability for surface pollutants (Skov & Durinck 1992; Carter et al. 1993; Williams et al. 1995). Published comments on standardised methods often aimed at greater precision in abundance (biomass) estimates (Briggs et ...