MODELING ENVIRONMENTAL AND ENERGETIC EFFECTS ON FEEDING PERFORMANCE AND DISTRIBUTION OF SHAGS (PHALACROCORAX-ARISTOTELIS) - INTEGRATING TELEMETRY, GEOGRAPHICAL INFORMATION-SYSTEMS, AND MODELING TECHNIQUES

The shag (Phalacrocorax aristotelis) is an important avian member of t he inshore, marine community. It is a foot-propelled pursuit-diver, fe eding predominantly on lesser sandeels (Ammodytes marinus), which it c atches mainly on, or near, the seabed. A Geographical Information Syst em (GIS) was used to integrate data on diving behaviour and feeding ra tes of shags with spatial information on three environmental variables : distance from the nearest breeding colony, water depth, and seabed s ediments, the last-mentioned being used as an indication of sandeel di stribution. The results are used to assess how differences in the mari ne environments in two areas of east Scotland might influence the feed ing performance and distribution of shags. Output from the model indic ates a highly dynamic situation in both areas, brought about by changi ng energy requirements of the birds through the season and variations in food supply, superimposed on a heterogeneous physical environment. In order to test qualitatively whether predicted daily feeding time wa s a good predictor of the observed distribution of birds on the sea, d ata from ship-based surveys were compared with spatial patterns of fee ding times. For both study areas, the relative frequencies of where bi rds were recorded on the sea were lower in areas where the predicted d aily feeding time was high. Limitations of the current model and futur e applications for this approach are suggested. (C) 1997 International Council for the Exploration of the Sea.