Daytime roosting and habitat preference of capercaillie Tetrao urogallus males in spring - the importance of forest structure in relation to anti-predator behaviour

Radio-equipped adult capercaillie Tetrao urogallus males (N = 10) were trac ked during April and May 1996-1997 in a coniferous forest in southeastern N orway, which has been subjected to clear-felling and replanting during the last five decades. With the use of radio-telemetry daytime habitat preferen ce was investigated at two levels of scale: within home range and within fo rest stands inside home ranges. In addition, roosting habitat preference wi thin stands was investigated by locating heaps of intestinal faeces, hencef orth called roosting sites. Within forest stands, forest structure and visi bility were measured at roosting sites (N = 94) and at random plots (N = 18 8). Within home ranges the birds used plantations and old naturally regener ated forest according to availability, and open bogs were avoided. Of the r oosting sites, 90% were located underneath the low branches of Norway spruc e Picea abies trees. For roosting within old naturally regenerated stands ( > 70 years old) males preferred sites with higher tree density, higher vert ical and horizontal cover and lower visibility than in the surrounding fore st. In young and middle-aged plantations, on the contrary, roosting sites t ended to have lower tree density (P = 0.118), but still seemed to have bett er cover than the surrounding forest (P = 0.117). The forest structure pref erence of roosting sites was reflected in the use of vegetation types withi n the old naturally regenerated forest. Because dense cover reduces the pro bability that the birds are detected by a predator, but at the same time in creases the risk of being killed once detected, capercaillie males have to compromise between shelter and outlook. Our data indicate that males prefer goad cover at the expense of good overview of the surroundings when select ing roosting sites, and that tree density is usually too dense in younger p lantations, probably because outlook is reduced and flying obstructed.