Behaviour and ecology

The western capercaillie is adapted to its original habitats—old coniferous forests with a rich interior structure and dense ground vegetation of Vaccinium species under a light canopy. They mainly feed on Vaccinium species, especially blueberry, find cover in young tree growth, and use the open spaces when flying. As habitat specialists, they hardly use any other forest types.

Western capercaillie, especially the hens with young chicks, require a set of particular resources which should occur as parts of a small-scaled patchy mosaic: these are food plants, small insects for the chicks, cover in dense young trees or high ground vegetation, old trees with horizontal branches for sleeping. These criteria are met best in old forest stands with spruce and pine, dense ground vegetation and local tree regrowth on dry slopes in southern to western expositions. These open stands allow flights downslope and the tree regrowth offers cover.

In the lowlands such forest structures developed over centuries by heavy exploitation, especially by the use of litter and grazing livestock. In the highlands and along the ridges of mountain areas in temperate Europe as well as in the taiga region from Fennoscandia to Siberia the boreal forests show this open structure due to the harsh climate, hence offering optimal habitats for capercaillie without human influence. Dense and young forests are avoided as there is neither cover nor food and flight of these large birds is greatly impaired.

Diet

The western capercaillie lives on a variety of food types, including buds, leaves, berries, insects, grasses and in the winter mostly conifer needles; you can see the food remains in their droppings, which are about 1 cm in diameter and 5–6 cm in length. Most of the year the droppings are of solid consistency, but with the ripening of blueberries, these dominate the diet and the faeces become formless and bluish-black.

The western capercaillie is a highly specialized herbivore, which feeds almost exclusively on blueberry leaves and berries along with some grass seeds and fresh shoots of sedges in summertime. The young chicks are dependent on protein-rich food in their first weeks and thus mainly prey on insects. Available insect supply is strongly influenced by weather—dry and warm conditions allow a fast growth of the chicks, cold and rainy weather leads to a high mortality among them.

During winter, when a high snow cover prevents access to ground vegetation, the western capercaillie spends almost day and night on trees, feeding now on coniferous needles of spruce, pine and fir as well as on buds from beech and rowan.

In order to digest this coarse winter food the birds need grit, small stones or gastroliths which they actively search for and devour. Together with their very muscular stomach, these gizzard stones function like a mill and break needles and buds into small particles. Additionally western capercaillie have two appendixes which grow very long in winter. With the aid of symbiotic bacteria, the plant material is digested there. During the short winter days the western capercaillie feeds almost constantly and produces a pellet nearly every 10 minutes.

The abundance of western capercaillie depends—like in most other species—on habitat quality, it is highest in sun-flooded open, old mixed forests with spruce, pine, fir and some beech with a rich ground cover of Vaccinium species.

Spring territories are about 25 hectares per bird. Comparable abundances are found in taiga forests. Thus, the western capercaillie never had particularly high densities, despite the legends that hunters like to speculate about. Adult cocks are strongly territorial and occupy a range of 50 to 60 hectares optimal habitat. Hen territories are about 40 hectares. The annual range can be several square kilometers (hundreds of hectares) when storms and heavy snowfall force the birds to winter at lower altitudes. Territories of cocks and hens may overlap.

Western capercaillie are diurnal game, i.e. their activity is limited to the daylight hours. They spend the night time in old trees with horizontal branches. These sleeping trees are used for several nights, they can be mapped easily as the ground under them is covered by pellets.

The hens are ground breeders and spend the night on the nest. As long as the young chicks cannot fly the hen spends the night with them in dense cover on the ground. During winter the hens rarely go down to the ground and most tracks in the snow are from cocks.

Дата добавления: 2015-11-16