Marking of deer fences to reduce frequency of collisions by woodland grouse.

Abstract

Recent studies of the effects of deer fences on tetraonids have concluded that fences are an important cause of mortality in woodland grouse. This 2-year study involving 16 sections of fences in the Scottish Highlands evaluates the effectiveness of making fences highly visible by using orange netting to reduce bird collisions with fences. A total of 437 collisions involving l3 bird species were recorded. Red grouse (Lagopus lagopus scoticus) formed 42% of all collisions, with black grouse (Tetrao tetrix) 29% and capercaillie (T. urogallus) 20%. Allowing for corpse removal by scavengers, an estimated 70% of red grouse and 29% of black grouse collisions were fatal. Black grouse and capercaillie both collided with 11 of the 16 fences at mean rates of 1.3 and 0.9 collisions km^-I year^-I, red grouse collisions occurred at l3 fences, with a mean rate of 1.6 collisions km^-I year^-1. Fewer grouse collisions occurred in the summer. Three quarters of black grouse collisions were by males. Collision rates were positively correlated with indices of black grouse and capercaillie abundance. Fence marking reduced capercaillie collisions by 64%, black grouse by 91% and red grouse by 49%. Although marked fences reduced capercaillie collision rates, they still remained an important cause of mortality. To conserve capercaillie, fences need to be removed altogether pending increased deer culls that would allow woodland regeneration without fences, or 'grouse friendly' fences designed.