Dunlin Calidris alpina alpina in The Solent, southern England

Abstract

The numbers of dunlin Calidris alpina alpina counted in Britain and Northern Ireland in winter declined by 50% between 1973/74 and 1987/88, although they have since increased somewhat. In The Solent, an estuarine system on the central south coast of England, numbers declined in some estuaries but were maintained in two large intertidal basins, Langstone and Chichester Harbours. We examine the physical characteristics of The Solent estuaries and conclude that those in which dunlin declined were suboptimal habitat because of their tidal and geomorphological peculiarities and, in one case, because of the loss of the main roost site. Recently it has been suggested that the spread of cord-grass Spartina anglica in individual estuaries was causally implicated in the national decline through a reduction in the area available for feeding. This was not so in The Solent, where Spartina is in decline. This tends to suggest that although the spread of Spartina may have been a proximate cause of dunlin declines in individual estuaries it is less likely to be the ultimate cause of the national decline. We review the population history of the dunlin in The Solent and conclude that the dominant influence on numbers this century was hunting mortality. Since the 1950s there has been a progressive increase in dunlin numbers in The Solent, which we suggest reflects release from hunting pressure. We speculate that in the context of this long-term trend the recent decline may prove to be a short-term oscillation.