Contemporary mature forest cover does not explain the persistence of Capercaillie (Tetrao urogallus) lekking areas in Finland

摘要

Capercaillie (Tetrao urogallus) has traditionally been considered an old forest-dependent species. The lekking sites especially,were thought to be located in older forests. We studied the persistence of Capercaillie lekking areas in relation tomature forest cover at three study areas in Finland (southwestern, SW; central, CE; and northern, NO). Atotal of 381 leks were inspected twice at intervals of 10-30 years and were classified as either persisting or vacated. We defined mature forest as forest with > 152 m ~3ha ~(-1) of timber (SW and CE Finland) or > 68 m ~3ha ~(-1) of timber (NO Finland). We measured mature-forest cover within two radii around the leks (1,000 and 3,000m) using satellite image-based forest inventories, and performed logistic regression analyses on these data. We did not find significant trends between mature-forest cover and lekking-area persistence in any of the study areas. However, the proportion of mature forestsmay have already been too low to detect the significance of this factor. The only significant factor affecting the lekking-site persistence was time lag between surveys. The positive relationship between the time lag and lekking-site persistence in CE and NO Finland may be due to the partial recovery of the landscapes in terms of forest regrowth, from extensive clear-cut harvesting in the 1950s and 1960s. In SWFinland, the relationship was negative, possibly indicatingmore permanent changes in the landscape that is currently characterized by human settlements and agricultural areas. We conclude that in present-day Finland, the area covered by mature forest ismost likely too scarce to explain the lekking-area persistence of Capercaillie. An alternative explanation is that some important structural characteristics are missing from the current mature forests.