Estimates and population consequences of tetraonid mortality caused by collisions with high tension power lines in Norway

1. Capercaillie, black grouse and willow ptarmigan mortality resulting from collisions with high tension power lines (11-420 kV) was estimated, based on the number of casualties found per kilometre of power line patrolled in three boreal forest and low alpine areas. 2. The length (km) of high tension power lines crossing tetraonid habitats was estimated using Geographical Information Systems and general knowledge about species-specific habitats. Of the entire Norwegian high tension power-line grid system (about 95 000 km), 55% was estimated to cross capercaillie habitats, 56% black grouse habitats and 16% willow ptarmigan habitats. 3. Because of biasing factors related to data-collecting procedures, the number of collision victims found per kilometre of power line patrolled was increased by a factor varying from 6.0 to 14.9. The estimated losses were about 20 000, 26 000 and 50 000 for capercaillie, black grouse and willow ptarmigan, respectively, which are about 90%, 47% and 9% of the annual hunting harvest of these species. 4. It was concluded that this estimating procedure may be useful to wildlife management authorities to assess losses caused by overhead wires in general. Locally, this mortality factor should be carefully recorded and considered together with other mortality factors like hunting, to avoid overexploitation.