Rolstad, J., Wegge, P. & Gjerde, I. 1997: Capercaillie Tetrao urogallus leks in fragmented forests: a 17-year study of the Varaldskogen population, southeastern Norway. - Wildl. Biol. 3: 293.
The population dynamics of capercaillie Tetrao urogallus was studied at Varaldskogen in southeastern Norway from 1979 to 1996. The long-term objective was to understand the mechanisms that drive population dynamics in time and space at different spatial scales (single lek: 100 - 1,000 ha, multi-lek: 5,000 - 15,000 ha, and regional: 50,000 - 100,000 ha). The dynamics of displaying males at the single and multi-lek scale within a central area of 5,000 ha are reported. Questions asked were: how are number and spacing of displaying males affected by large-scale logging, and what are the consequences for female choice and matings? Three leks were subject to large-scale logging and three leks served as controls. These leks were censused each year and the surrounding areas were searched for single displaying males and new leks. Yearly production of chicks was estimated from August censuses with trained dogs. The number of displaying males (N = 84, 2 years) fluctuated between 13 (1985) and 34 (1982) and those of females (N = 84, 1 year) between 40 and 70. Yearly changes in numbers of displaying males were highly correlated with August counts of chicks two years before (R² = 0,60; P < 0.001). The population peaked in 1982, 1989, and 1996 at 7-year intervals. Within the area of the three logged leks the proportion of old (> 70 years) unmanaged forest decreased from 50 to 15%, whereas the area of the three control leks experienced a decrease from 50 to 40%. The average yearly densities of males did not differ between the logged (5.8/1,000 ha) and the control leks (6.8/1,000 ha) during the first 7-year period (1982-88: t = 1.7; df = 6; P = 0.14), but differed during the second 7-year period (1989-95) with 5.4 and 7.9 males/1,000 ha, respectively (t = 2.9; df = 6; P = 0.03). The three logged leks split into several smaller leks and single displaying males, whereas displaying males at the control leks remained highly clumped. During 1987-1996 the number of mating sites in the logged areas almost doubled (5.4 sites) compared to the control area (3 sites). The results are ambiguous regarding the effects of logging on the number of displaying males. However, logging clearly caused the clumped lek system to split into a dispersed pattern of smaller leks and single displaying males. This probably constrained female choice of mates, giving rise to a more even distribution of matings among the males.
Key words: capercaillie, fragmented forests, leks, Norway, Tetrao urogallus
Jorund Rolstad, Norwegian Forest Research Institute, Hoyskoleveien 12, N-1432 Ås, Norway
Per Wegge, Department of Biology & Nature Conservation, Agricultural University of Norway, P.O. Box 5014, N-1432 Ås, Norway
Ivar Gjerde, Norwegian Forest Research Institute, Fanaflaten 4, N-5047, Fana, Norway