A new survey method for Water Shrews ( Neomys fodiens ) using baited tubes

The Water Shrew, Neomys fodiens, is one of Britain’s least known mammals. Although it has a wide geographical distribution within the British Isles, it has a sporadic and localized occurrence, and remarkably little is known about its habitat requirements. The Water Shrew has never been the subject of a nationwide survey in Britain, and evidence of its occurrence is patchy. Although a number of field studies have elucidated much about its population dynamics, feeding ecology and movement patterns (e.g. Shillito, 1963; Wol ¢k, 1976; Churchfield, 1984a,b; Van Bemmel & Voesenek, 1984; Lardet, 1988; Cantoni, 1993; Castien, 1995), little is known of its habitat preferences, and its current conservation status remains unknown. It is an elusive species which leaves little evidence of its presence. Any field signs remain well hidden amongst the vegetation, so it does not easily lend itself to a wide-scale survey. The usual methods of surveying small terrestrial mammals by live-trapping or hair-tubes (Dickman, 1986) are expensive and/or labour-intensive. In order to encourage surveys of Water Shrews over a large area and a range of habitats an alternative economical method is required. The method devised here was based on the observation that shrews (including Water Shrews) readily investigate novel objects and frequently defaecate on and inside such objects. The appearance, consistency and contents of the scats can provide a guide to the species which has produced them. The remains of aquatic invertebrates (e.g. Asellus aquaticus, Gammarus pulex and Trichoptera larvae) in scats confirms the presence of Water Shrews, as coexisting terrestrial shrews very rarely feed on these prey (Churchfield, 1984a). These prey are easily identified in scats by scanning with the aid of a binocular microscope; the presence of freshwater crustaceans can often be detected with the naked eye.