Tercera Etapa (1998 – 2000)

There are several steps to establishing a GRANNY score. In the first instance the landscape metrics (edge to area ratio, nearest neighbour distances etc) of a forest are calculated. This provides an assessment of the extent of fragmentation of the forest. Forest fragmentation is known to adversely affect the persistence of capercaillie populations (e.g. Menoni & Bougerol 1998, Stewart 2000, Wegge 2005). If the forest is highly fragmented then a low score is given to an area of woodland. The quantity of blaeberry (Vaccinium myrtillus) and heather (Calluna vulgaris) on the forest field layer is also believed to be an important determining factor in the persistence of capercaillie populations (e.g. Moss & Picozzi 1994; Moss 2002).

The quantity of these plant species on the forest field layer is recorded and the higher the percentage of cover, the higher the GRANNY score given for that particular woodland feature. The structure and tree species that make up the forest or woodland stand are also known to affect the survival of a population of capercaillie (e.g. Moss et al 1978, Moss & Picozzi 1994, Summers 1997). Thus the height and age of the trees in the forest, the species of tree growing and the level of spacing between the trees are all recorded and given respective scores. Each of these scores is then added together to produce the final GRANNY end-score; the higher the end-score the more suitable the area of woodland is for the capercaillie.

The GRANNY score developed in Scotland during in the 1990s considered the suitability of an area of woodland on a regional scale, considering the entire forest area. In recent years interest has grown in the micro-determinants of capercaillie habitat selection (e.g. Sachot et al 2003; Summers 2004). One such Habitat Suitability Index (HSI) examining factors on a smaller scale was developed by Storch in 2002 using data gathered in the Bavarian Alps. Suchant et al (2003) build on the model produced by Storch (2002) to develop an integrated habitat model for capercaillie and chamois (Rupicapra rupicapra) in the Bavarian Alps that allows for the integrated management of woodland for more than one species.

Despite their popularity amongst conservation managers Habitat Suitability Indexes for populations of capercaillie are difficult to rationalise. This is primarily due to the variation between the male and female capercaillie habitat preferences; and the variations encountered when applying the findings from the models when examining

different countries. During the winter months the different sexes have similar habitat needs (Jones 1982). However, during the spring and summer months the habitat requirements between the sexes become different and specific. The location of lek sites, the communal display grounds are also usually located in areas of different habitat within a forest. The selection of lek sites by the species has been particularly difficult to quantify. In his study of eleven different capercaillie populations in Sweden, Hjorth (1981) noted five major features of lek site habitat. The habitat attributes identified by Hjorth (1981) included areas with a firm ground portion and a part of the pine bog, a certain amount of ‘vegetational or topographical curtain’ towards the surroundings of the arena, some aged pines, a certain amount of tall shrubs or dwarf trees under the woodland canopy and one or more open space free from herbs, tall grasses or shrubs.

Radio tracking studies of the habitat requirements of the species in the Bavarian Alps have shown that the species has a specific preference for areas of ‘old growth forest’ with a 50% canopy cover and a well developed forest field layer containing blaeberry (Storch 1993). Similarly, studies that have been carried out in Sweden have shown that capercaillie express a preference for a mosaic (greater than 6% of the forest) of different woodland habitats and woodland that is over 40 years in age (Jansson & Andren 2003). This preference for areas of old growth open woodland is mirrored in the capercaillie populations in the Jura Mountains in Switzerland (Sachot 2005). Here capercaillie have shown no negative preference towards woodland at high altitudes (1100-1600 metres) or to the level of exposure of the woodland. This goes against the findings of other HSI models. The species was also observed in the Jura Mountains selecting areas of open forest, indeed some of the areas selected are also reported to have forest field layers that had been grazed by cattle. Here the species avoided areas of woodland with a dense understory or undercanopy and selected forests that had a canopy cover of around 30% and a forest field layer with a 20% cover (Sachot et al 2003; Sachot 2005). This illustrates dramatically the variation in findings between different HSI models produced in different European countries.

There have been several estimates of the natural density that the species occurs at in woodland however these seem to vary with location throughout the global range of the capercaillie (Grimm & Storch 2000). Marshall and Edwards-Jones (1998) stated

that natural carrying capacity of capercaillie in natural habitat is about 30 birds in 1000 hectares of woodland. They also state in this study that in order for a species to have a greater than 95% chance of survival over a fifty year period that the minimum viable population (MVP) size should be 60 individual birds in 5000 hectares of habitat. Grimm and Storch (2000) on the other hand state that in order for the chance of extinction of a population of capercaillie not to exceed more than 1% over a 100 year period the MVP is actually in the region of 470 individual birds in an area of 250 km² of suitable habitat. This represents a difference of about 30 hectares per individual bird, one estimate stating that each capercaillie requires around 83 hectares and the other only 53 hectares.

Diet & Foraging Behaviour

The feeding habits of the capercaillie are seasonal and can be separated into three distinct categories: (1) winter food (2) inter-seasonal food and (3) summer food (Jones 1982). The needles of the Scots pine are the dominant winter food of the capercaillie and during this period the species is normally found feeding in the crowns of trees (Palmar 1965, Storch 2005). Although the species exhibits a marked preference towards Scots pine the needles of larch, firs and spruces are also eaten, in descending order of preference (Moss & Picozzi 1994). During the spring and summer months the capercaillie feeds on the ground and takes a variety of ground vegetation that is largely composed of the leaves, flowers, berries and other material of suitable plants as well as a variety of herbs, mosses and sedges (Jones 1982).

An important habitat component across much of their distribution, including Scotland, is a forest field layer dominated by the floral species of blaeberry and ling heather (Plate 13) (Storch 1993; Moss & Picozzi 1994). These species are associated with mature pine forests in Scotland that have a relatively open woodland canopy and they provide food and cover for the capercaillie hen and her brood (Moss et al 1978). Blaeberry and heather are also an important source of lepidopteron larvae which provide protein that is essential for the development of the chicks (Picozzi et al 1999). Similarly, woodlands containing areas of bog vegetation are also particularly beneficial to the capercaillie, providing invertebrate larvae, moss fruiting bodies as well as grass and sedge inflorescences as food for both the adults and the young (Sjoberg 1996). Capercaillies are also known to eat the shoots and buds of deciduous

trees including birch (Betula spp.), rowan (Sorbus spp.), willow (Salix spp.) and oak (Quercus spp.) (Jones 1982).