Use of aspen Populus tremula by Capercaillie Tetrao urogallus in southeastern Norway

Abstract

The use of aspen Populus tremula by 27 Capercaillies Tetrao urogallus equipped with radio transmitters was recorded at Varaldskogen, southeastern Norway, during MayOctober, 1986-87. Males were observed in aspen at 23 of 301 checked locations, while females were recorded only once from 88 . Males used aspen in two distinct periods, 29 May-30 June and 25 August-6 October. The frequency of male locations in aspen was four times higher in early summer than in autumn . Some males most probably actively selected aspen trees, while others did not use aspen at all. Modern forestry practice may reduce thedensity of aspen trees below a thresholdvalue which prevents birds from taking advantage of this food source.