Spatial endangerment of capercaillie (Tetrao urogallus L.) populations in Slovenia in 1998
1999
Cas, M. (Slovenian Forestry Inst., Ljubljana (Slovenia))
In 1998, 473 hunters and foresters participated in a repeated pan-Slovenian survey of capercaillie (Tetrao urogallus L.) leks activities in 1.234 observations. Out of the total of 559 surveyed leks only 273 (49%) are still active. Out of 495 leks (88.6%) in the Alpine region 51% were established as active and of the other 64 leks in the Dinaric region 33%. Active populations are present in 74% of the surveyed distribution area. 83% of the distribution area have been preserved in the Alpine (0.22 birds/km**2) and 19.7% in the Dinaric region (0.07 birds/km**2) in 4 839 km**2 or 22% of Slovenian area. The share of active leks in forests in 200 m- altitude zone areas increases linearly, from only 16% of active leks from 601 to 800 m above sea level to 70% from 1.401 to 1.600 m (timber line is at 1.650 m). Below 1.000 m there are only 11.2% of all active leks. The optimum of population density was established from 1.201 to 1.600 m in 66% of all active leks, with 0.59 birds and 0.18 of active lek/km**2. After 1986 the number of active leks has fallen by 199 (42%), 41% of this in the Alpine and 53% in the Dinaric region. The number of deserted forest leks grows linearly with decreasing in 200 m - altitudinal zones, from 22,9% from 1.400 to 1.600 m to 78,9% from 601 to 800 m. Deserted or most endangered are the margin distribution regions in the sub-Alpine region and in the entire Dinaric region. The greatest number of sub-populations has been preserved in remote high-altitude Norway spruce and beech forests.
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