The lengths of fences in Highland woods: the measure of a collision hazard to woodland birds

Abstract

Birds die due to collisions with many static man-made objects, particularly wires (powerlines, ski-tows and fences) (Avery, 1978; Faanes, 1987; Bevanger, 1990; Alonso et al., 1994). Although these events are common, the effect that fatal collisions have on bird populations has rarely been studied. Catt et al. (1994a) found that capercaillie (Tetrao urogallus L.) living in native pinewoods in Scotland collided at a rate of 3 collisions km' a~' against 1.8 m high deer fences. This led to an annual mortality of 32 per cent, higher than all other causes of mortality combined. Further work showed that collisions against deer fences, particularly by gamebirds, were widespread in the Highlands of Scotland. In one year, 115 red grouse Lagopus lagopus (L.), 25 black grouse Tetrao tetrix L. and 31 capercaillie collided with 134.8 km of fences in and around woods, primarily conifer plantations. Smaller numbers of owls, pigeons and passerines also died (Petty, 1995; Baines and Summers, 1997). These mortalities are of conservation concern, particularly because capercaillie and black grouse are two of 23 species which have declined by over 50 per cent in