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Capercallie: A Review of Research Needs

SUMMARY

1 The capercaillie is a red-listed species in Scotland where it has undergone a dramatic reduction in number and range over the last 20-25 years. In spite of much recent research, which has led to a better understanding of capercaillie requirements, the objectives of the Government's Species Action Plan will not be achieved unless the decline can be halted. In an attempt to arrest or reverse this decline, a review of the European literature has been undertaken to identify factors contributing to this decline. Research needs are prioritised and improvements in conservation practice that would benefit capercaillie are recommended.

2 Native capercaillie became extinct in 1783, largely due to previous deforestation. The successful re-establishment from 1938-39 coincided with the maturing of large areas of forest planted on estates during 1750-1850 and with intense predator control that eliminated entire predatory guilds from areas managed for gamebirds. Numbers reached a peak during 1910-30 and again during 1960-75. Since then numbers have declined and breeding range has contracted to the central Highlands. Two recent estimates indicate that numbers fell from around 2200 birds in 1992-94 to 1073 birds in 1998-99. Overall, conifer plantations have lower densities than semi-natural pinewoods, but the area of plantation is far greater, and with appropriate management could provide a substantial resource for capercaillie.

3 The habitat requirements and diet of adults are reasonably well known. Adults are almost entirely herbivorous. They forage mainly in the crowns of large coniferous trees in winter where they eat needles, buds and twigs. Scots pine comprises a large part of their winter diet in Scotland, but other coniferous species are also eaten. A transition to feeding on ground vegetation occurs in spring and the reverse happens in autumn. Diet is more varied during the period of ground feeding due to the sequential exploitation of seasonally available foods. Important foods are new shoots and flower buds of broadleaved trees, dwarf shrubs and cotton grass, and seeds of sedges and berries from dwarf shrubs. Males display communally at sites called leks. In continuous forest, leks are spaced about every 2 km and the number of males at a lek is related to the amount of old forest within 1 km of the lek. Many habitats at present appear to have fewer capercaillie than they are capable of supporting. Food-supply and habitat availability for adults appear unlikely to be factors responsible for the current decline.

4 Most chicks hatch during the first week in June. They are dependent on insects for food until 3-4 weeks of age after which they gradually switch to a largely herbivorous diet by 6-7 weeks of age. Insects provide protein-rich food necessary to sustain the rapid early growth of chicks. Females lead newly-hatched chicks to insect-rich areas called brood habitats. Blaeberry, which grows as an understory shrub in woodland on well-drained soils, provides one of the most important brood habitats due to the abundance of moth larvae that eat its leaves. Damp sites with lush vegetation also provide insect-rich areas for broods. The quality of brood habitats is adversely affected by heavy grazing, particularly by red deer. High densities of deer result in short vegetation that offers little shelter or food for chicks. Culling deer to less than 5 deer km² can reverse these negative effects of grazing, but in open woodland blaeberry is gradually replaced by heather, which then provides a poor brood habitat. A substantial improvement in the quality and extent of brood habitats is one of the key factors that may help capercaillie to recover.

5 Breeding success has been estimated from counts made in August, when dogs are used to flush broods. This is at a time when chicks can still be distinguished from adults. Breeding success appears to have declined from around 1.8-2.2 chicks per hen in the late 1970s and early 1980s to around 0.9 chicks per hen during 1991-97. This appears to be the main factor responsible for the current decline. Poorer breeding success appears to be linked to a complex interaction of numerous factors. These include (i) poorer spring weather conditions that may affect both the quality of food available to hens prior to laying in late April and the survival of young chicks in early June, (ii) increased predation levels on nests and chicks, (iii) and the impoverishment of brood habitats, due mainly to overgrazing by deer (4 above). While nothing can be done about climatic deterioration, management should, in theory, be able to address the latter two factors.

6 The survival of adults may be lower now than in the past. However, estimates of survival are based on relatively small sizes and should be treated cautiously. Nevertheless, collision with deer fences is now the main cause of mortality in adults and this appears to be the main reason for lower survival rates. Marking deer fences with visible strips of orange netting reduces collisions, but it does not eliminate them. The only way to resolve the problem is to move more quickly towards culling as the main means of limiting deer numbers, and to accelerate the removal of internal forest fences.

7 A suite of research projects is identified to address the most important factors identified in the review as being linked to the current decline. These are designed mainly to improve our understanding of biotic factors associated with poor breeding success, but also to help resolve problems with deer fence collisions. There is a danger that any time lag associated with undertaking research, implementing the findings and these having the desired effects on population recovery will be too long. Therefore, in addition to the research recommendations a more pragmatic targeted approach to management is required.

8 A three-tier classification of the most important areas for capercaillie is described. Core areas include the most important capercaillie habitats and populations. Extension areas have less prime habitat and fewer capercaillie, but nevertheless provide suitable habitat into which capercaillie could expand their range following improvement in breeding success in core areas. Within core areas, the most important sites are currently being identified, which are called key areas. To start reversing the current decline these key sites need to start exporting surplus birds to adjacent areas. A management package is proposed where the greatest input into improving habitats is targeted at key sites, but with substantial input into improvement of remaining core and extension areas.

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