Changes to the Common Scoter populationwinteringoffDornoch, Moray Firth, Highland

D. PATTERSON, D. MACASKILL, D. TANNER & J. GRAHAM

Common Scoters have been present in exceptional numbers off Dornoch, within the Outer Dornoch Firth Section of the Moray Firth Special Protection Area (SPA), for at least three consecutive winters. The sustained pressure of c. 6,000 foraging scoters on their prey resource may have caused a progressive change in scoter feeding distribution during late winter. Common Scoters moved away from their primary forage site earlier each year, relying increasingly upon a secondary forage zone along the open coast. The requirements for a sufficiently large/high quality forage resource to support such a large population at this latitude, combined with birds switching to a secondary forage zone during cold temperatures, may have caused a proportion of scoters to vacate the study area in late winter.

Introduction

In Scotland, as in other parts of their range, large wintering flocks of Common Scoters Melanitta nigra congregate in shallow inshore areas, frequenting water depths of c. 20 m, where they dive to forage within soft substrates on the seabed (Forrester et al. 2007). Their diet comprises mainly bivalve molluscs, with other species incorporated less frequently, such as small crabs, small fish and gastropods (Madsen, 1954). The benthic prey within these sedimentary habitats is strongly influenced by sea-bed hydrodynamic stress and hence this can be an important determinant of benthic distribution. Therefore, food resources available to Common Scoter are unlikely to be uniformly distributed, with certain areas of seabed yielding higher rates of energy intake than others (Kaiser et al. 2006).

The Moray Firth has previously been identified as the most northerly UK stronghold for Common Scoter (Forrester et al. 2007). It is now designated as a Special Protection Area for Common Scoter with an estimated non-breeding population of 5,479. The Moray Firth SPA also supports