Habitat selection and waterbody-complex use by wintering Gadwall and Shoveler in South West London: Implications for the designation and management of multi-site protected areas

Abstract

The degree to which Special Protection Area (SPA) designation reflects ecological reality is of critical importance to wildlife conservation. We examined whether the designation of a large SPA designated to conserve wintering waterfowl (chiefly Gadwall Anas strepera and Northern Shoveler Anas clypeata), reflected the birds’ habitat preferences and their use of the SPA in the context of the broader geographic area. To do this, 67 discrete waterbodies in and around the South-West London Waterbodies Special Protection Area (SWL SPA) were surveyed regularly each winter from 2004/5 to 2006/7, and new analytical methods developed, to investigate habitat selection and multiple-site use by the birds. Significant pressure on these waterbodies for mineral extraction, development and recreation, together with a long history of human usage has resulted in a wide range of habitats and conditions for these wildfowl.We found that Gadwall and Shoveler were able to adjust their site preferences and patterns of site use in response to changes in food resources and other ecological variables both within and between winters. Akaike's Information Criterion (AIC) was used to model the distribution of wildfowl between sites using a large number of physical and ecological predictor variables. This showed that Gadwall and Shoveler differ in many of their habitat preferences, to the extent that managing a site for one will not necessarily directly benefit the other.At the time of this study the habitat preferences of Gadwall and Shoveler do not closely match the ecological condition of the SWL SPA waterbodies. Furthermore, an investigation into the use of multiple sites by Gadwall and Shoveler indicated that although there is evidence for populations of wintering birds using groups of waterbodies in the SW London area, their patterns of site use do not closely match the distribution of the seven separate SPA component waterbodies.We provide guidelines for managing habitats for Gadwall and Shoveler, and suggest that in addition to bird counts the SPA designation process for multi-site protected areas should consider the behaviour, habitat requirements and the influence of human disturbance on the species concerned. In this instance, the patterns of wildfowl site use present a reasoned argument for the inclusion of additional sites in the SW London Waterbodies SPA, or for dealing with the SPA in a different manner to a site with a more contiguous boundary.