Tetrao Urogallus) Leks in a Scandinavian Mountain Range Area
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Examensarbete i ämnet biologi Distribution and structure of Capercaillie (Tetrao urogallus) leks in a Scandinavian mountain range area Per-Johan Gustafsson Photo by Kjell Sjöberg Handledare: Kjell Sjöberg 30 Poäng, D-nivå Vilt, Fisk och Miljö 2008:8 SLU 901 83 Umeå, Sweden Examensarbete i ämnet biologi Distribution and structure of Capercaillie (Tetrao urogallus) leks in a Scandinavian mountain range area Per-Johan Gustafsson Photo by Kjell Sjöberg Supervisor: Kjell Sjöberg 30 Point, D-Level Wildlife, Fish, and Environmental Studies 2008:8 Swedish University of Agricultural Sciences SE901 83 Umeå, Sweden Abstract The Capercaillie (Tetrao urogallus) is distributed along the whole Scandinavian mountain range, but so far few studies exist about habitat selection, reproductive success, survival rate, lek structure and distribution, etc. of Capercaillie in this region. In this study, I searched for Capercaillie leks during the years 2003-2007 in valleys of the Scandinavian Mountain Range near the village of Tärnaby, Västerbotten County. In total, 20 lek sites were discovered, their locations in the landscape described, and the numbers of territorial males at each lek counted. Within the study area, the influence by forestry so far is small, compared to the situation on lower elevations and in more central part of the boreal forest region where most capercaillie studies have been performed. Observation of Capercaillie males in the study area suggests that the distribution of leks and the number of attending Capercaillie males is different than in other parts of Fennnoscandia. The lek sites were typically found in the upper parts of the coniferous forest, in the edge between the spruce and birch vegetation belts, or in forests mixed with Norway spruce (Picea abies) and birch (Betula pubescens ssp. Czerepanovii). The height of the forest varied from 0 to 25 m, but tree height of 10 to 18 m was preferred in areas of the leks. In lower parts of the valley, leks were also found in broader belts of coniferous forest. Keywords: capercaillie, Tetrao urogallus, Scandinavia, mountain range, leks, solitary display, edge zone, juniper Page 2 Introduction The Capercaillie (Tetrao urogallus) is a large, dimorphic grouse that is distributed from Scotland to central Siberia and Altai in the east, from 70oN in the north to 40o N in the south. It is not equally distributed within this distribution range. In southern Europe, for example, it is mainly found in mountain regions (Johnsgard 1983, Ahlén and Tjernberg 1996). This big woodland grouse has been characterized as a bird preferring old coniferous forests (Hjort 1994). The species seem to have undergone a general decrease in Sweden during the last decades (Svensson et al. 1999). The most accepted explanation for this is fragmentation of habitats due to modern forestry and management (Storch 2001). For example, clear-cuts become impoverished for several years for this woodland grouse (Gjerde and Wegge 1989). Spacing is necessary for the survival of a species, but also for fitness and reproductive success (Begon et al. 1999). In birds, males often spread out shorter distances than females, while the opposite is common among mammals, where the females more often stay near the place they are born (natal philopatry, Greenwood 1980). Capercaillie cocks often establish near their natal site (< 4 km), while females often disperse up to 30 km (Koivisto 1963 in Storch 2001). After establishing at a lek at the age of two or three years, territoriality and site fidelity remain strong in adult males (Wegge and Larsen 1987). They are thought to stick to their home range most of the year for the rest of their life. Therefore it is evident that the habitat has to provide at least such fundamental requirements as food and protection even during the harsh period of the year with snow covering the ground and subsequently during a period when some of the food is not available to the birds (Gjerde and Wegge 1989). A number of mating systems are found in grouse species. Indeed the tetronidae is the group of birds that shows the widest range in mating systems (Höglund and Alatalo 1995). However, it is suggested that other mating systems has evolved from non-lekking arrangements. Many grouse species have both lek mating and non-lek mating populations. The Capercaillie is a polygynous species where males and females only meet at certain sites, display grounds, lek sites or leks, for mating. After establishing at a lek, the males stay within their home range most of the year. In February the male may start their display activity and it normally culminates in the late April or beginning of May. During the entire displaying period, site fidelity is strengthened and the male is seldom far away from the lek site, which normally is situated at the edge of his home range (Hjort 1994, Gjerde and Wegge 1989, Storch 1995a). This lek site is by definition shared by more than one male, and each male has his own home range in connection to the lek (Hjort 1994, Wegge and Larsen 1987). From studies of very large leks (>25 males), it could be concluded that Capercaillie males have individual territories on the lek, but in their home ranges they demonstrate a social system with a hierarchical organization in such a way that adult males are territorial, regardless of breeding status, when they attend the lek. Off the lek, it is only high ranked males that demonstrate their higher status (Wegge et al. 2005). Leks or display sites are typically consecutive from year to year (Wegge and Larsen 1987). In winter and spring, including the lekking period, males tend to stay within a 1 km radius of the lek, but outside the lekking period they disperse within a 3 – 4 km radius, sometimes more, during summer. At the end of the winter the Capercaillie often shows a strong preference for small parts (0.1-0.5 ha) of the home range (Gjerde 1990a). Page 3 Studies of Capercaillie lek arrangement and spacing have been conducted for example in Russia (Beshkarev et al.1995), Estonia (Viht 1997), Northern Europe (Wegge and Larsen 1987), Central Europe (Storch 1997), Slovakia (Saniga 1996a), the French Pyrenees (Catusse 1993) and Scotland (Picozzi et al. 1992). A more or less even distribution of Capercaillie leks is found in areas with coniferous forests. However, in the highest parts, close to the timberline in the Alps, a different pattern is observed. There the Capercaillie leks are distributed like a string of pearls along the timberline (Hjort 1994). Apparently it is the territorial demands of the male Capercaillie which affects the distance between leks (Gjerde et al. 2000) and consequently leads to an even distribution of leks. Most of the Scandinavian studies of Capercaillie so far are done in the southern boreal forest (Wegge and Larsen 1987). In southern Europe, surveys have focused on capercaillie living in mountain habitat (Catusse 1993, Menoni 1997). In this thesis I present results from a study of Capercaillie lekking sites in an area almost undisturbed by forestry. Clear-cut felling in recent years has influenced only a few percent of the total area. Most other studies of Capercaillie in Fennoscandia are conducted in areas heavily influences by forestry. In my study area the Capercaillie are thus able to select lekking sites in forests with minor influence by forestry. The forested areas along the Scandinavian Mountain range, with typical vegetation zones dominated by either Norway spruce (Picea abies) or Scots pine (Pinus sylvestris) in the conifer vegetation belt and birch forests further up along the mountain slopes have not previously been examined with respect to Capercaillie lekking grounds. Based on the observational knowledge about the structure and distribution of Capercaillie leks in the region (for example that there seem to exist several small leks with only one or two displaying males), one main question in my study has been to find out whether males display solitarily or at communal display grounds. In addition, it is also interesting to document if solitary males choose other display sites than collectively-displaying cocks. Further, the study also includes some documentation of two of the fundamental requirements for survival of Capercaillie in the Scandinavian Mountain Range, i.e. food and shelter. My hypothesis or prediction is that in the forested valleys of the Scandinavian Mountain Range, the distribution and composition of the Capercaillie leks are more similar to the situation in the European Mountain Ranges like the Alps and Pyrenees Mountains than the situation in the areas in northern Sweden at lower elevations. Study area The study was conducted at Boksjödalen (65 40´ N, 15 50` E) situated in the mountain region in the northern part of Sweden, during winters of 2002–2007. The terrain is composed of an elongated valley with relatively moderate slopes. The altitude of the study area is 460 m a.s.l. at the bottom of the valley and the mountains reach altitudes of 800– 1400 m a.s.l. The total study area exceeds 7000 ha. Coniferous forests of Norway spruce dominate ca. 50 % (ca. 3800 ha) of the study area while the remaining ca. 50% is covered with Downy birch (Betula pubescens ssp. Czerepanovii). The hillsides of the valleys are typically wooded with spruce in the lower parts and birch in the upper parts. Norway spruce reaches 650-700 m a.s.l.. The coniferous Page 4 forest limit strongly sinks from the eastern part of the mountain to the western parts and this can be about 200 m (Rune 1974, Sjörs 1956). The birch forest in the mountains may reach 850 m a.s.l.. In the middle part of the study area there is mainly deciduous forest, but with a few larger forest patches (>100 ha) with spruce forest.