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Capercallie: A Review of Research Needs

2 CAPERCAILLIE: A REVIEW

2.1 Status and range

2.1.1 Statutory and voluntary designations

The capercaillie is listed on Annex I of the Birds Directive, Appendix II of the Bern Convention and Schedules 2, 3 and 9 of the Wildlife and Countryside Act 1981. The re-scheduling of capercaillie to Schedule 1 is currently under consideration.

It is a potential quarry species, but because of its decline in recent years a voluntary shooting ban has been in place on Forestry Commission and privately-owned land since 1990. This has been effective.

It was first included as a red data species by Batten et al. (1990) and subsequently red-listed by Gibbons et al. (1996). The later designation was based on a reduction of over 50% in its breeding range during the last 25 years.

The objectives and targets of the Government's Species Action Plan (UK Biodiversity Group, 1998) are:

To halt the decline, the causes of which are becoming clearer, and to restore the species to its former range.

Halt the decline in its core range in eastern and central Scotland by 2000.

Maintain, and expand where possible, the range and population numbers in Scotland to 20,000 (the status in the early 1970s) by 2010.

There is an active inter-agency Capercaillie Biodiversity Action Plan Steering Group, which includes the relevant government departments (FC, FE, ITE, DCS, SNH), NGOs (GCT, RSPB, SLF) and other informed individuals. The Scottish Executive is expected to join the Steering Group soon. This group holds regular meetings, and recently a Capercaillie Project Officer has been appointed (Anon, 1999) and funding by RSPB, SNH and the Forestry Commission.

2.1.2 Range

The world range lies within the boreal forest zone of northern Europe and Asia, with southern extensions into northern temperate and alpine zones in central and western Europe (Cramp & Simmons, 1980; Johnsgard, 1983; Marti & Picozzi, 1997; Klaus et al., 1989). In Europe, the main populations are in Finland, Norway, Russia and Sweden (Marti & Picozzi, 1997). The much smaller populations in Central Europe are more fragmented. These mainly restricted to the Alps, the Pyrénées, the Jura, the Carpathian and Cantabrian mountains. There has been an overall contraction in range throughout Europe, being most severe in the smaller and more isolated central European populations. The latest European population estimate, excluding Russia, is of 245,313 birds (Marti & Picozzi, 1997).

According to Cramp (1980), T. u. ugogallus occupies most of Europe, including central Europe and Fennoscandia eastwards into Asia. This is the race that was introduced into Scotland (see later). Three other races occur in Europe; T. u. aquitanicus in the Pyrénées and northwestern Spain, T. u. rudolfi in the southern and eastern Carpathians and T. u. taczanowskii in Russia south of nominate urogallus. However, this definition and distribution of races varies between authors [cf. Cramp, 1980 #128; Howard, 1998 #1006; Johnsgard, 1983 #2321].

2.2 History of capercaillie in Britain

2.2.1 The native population

The capercaillie was native to Britain and Ireland. Yapp (1983) considered that they were probably extinct in England by around 1300. In Ireland they survived longer, with a few still present in Co. Tipperary around 1760, but with no records after 1790 (Bannerman & Lodge, 1963; Hall, 1981; Hutchinson, 1989). Their demise in Scotland occurred around the same time. They were already scarce during the seventeenth century. It is generally accepted that the last survivors finally disappeared from Inverness-shire around 1770 (Harvie-Brown, 1888; Pennie, 1950; Pennie, 1951; Lever, 1977; Ritchie, 1920), although a few individuals appear to have survived until 1785 in upper Deeside (Bannerman & Lodge, 1963).

The demise of capercaillie in Scotland mirrored similar declines of other woodland species, all of which were linked to large-scale deforestation during the fifteenth to eighteenth centuries (Ritchie, 1920). A reversal in this trend happened during 1750-1850 when large areas of woodland were planted in Scotland, but this was too late to save the last native capercaillie. The Duke of Atholl planted 4000 ha of forest in Perthshire, much of which was larch. In the valleys of the Spey, Dee and Don large forests were also established, mainly of native Scots pine. In total over 200,000 ha of forest was planted on Scottish estates during this period (Holmes, 1975). Over hunting and a period of deteriorating climatic conditions may also have hastened their final decline (Moss & Picozzi, 1994).

2.2.2 The re-establishment in Scotland

Numerous attempts were made to re-establish capercaillie starting in the 1820s, but all initially failed (Lever, 1977). The first successful breeding occurred in 1838/39 in the grounds Taymouth Castle, Perthshire following the release of adult birds imported from Sweden in 1837/38. The following colonisation of Perthshire and beyond was dramatic and was aided by numerous subsequent introductions, both from the Perthshire stock and from more introductions of adults birds from Sweden, Norway, Finland and Austria (Bannerman & Lodge, 1963; Harvie-Brown, 1888; Pennie, 1950; Pennie, 1951; Ritchie, 1920). Success at establishing new populations was frequently achieved by placing capercaillie eggs in black grouse nests. This proved to be a more successful technique than using captive-reared birds.

Two factors appear to have been crucial to these early successes, in addition to the techniques used. The maturing of large areas of forest planted during 1750-1850 and intense predator control. The latter factor was probably crucial to the success. The timing of the re-establishment coincided with a growing interest in sporting estates and gamebird shooting, which persisted well into the twentieth century. During this period almost the entire predatory guild (mammals, raptors and corvids) was eliminated from some of the largest shooting estates in Scotland (Newton, 1972; Newton, 1979; Yalden, 1999).

Maximum distribution and numbers of capercaillie were reached by the time of the First World War, although some shooting bag data indicate a later peak in abundance (Figure 1a & b). It is hard to envisage just how abundant they had become by this time. They were a highly prized quarry species, with some substantial bags being recorded in the late nineteenth and early twentieth centuries. Of particular note was a bag of 150 shot on one day in 1908 on Blackhall Estate, Kincardineshire (Ritchie, 1920). The number of gamekeepers employed on estates in Scotland peaked around this time (1910) and thereafter declined to a low point by around 1950 (Figure 1c).

From the First World War until the early 1980s, numbers appear to have fluctuated with an overall downward trend, although there are few quantitative data from this period. One of the best data sets comes from shooting bag records from 26 Scottish estates during 1880 - 1985 (Figure 1a & b). Shooting bag data are unlikely to reflect population trends accurately due to numerous biases. For instance, less effort will have been put into shooting capercaillie, both during the war years and in years with fewer birds. Recording accuracy could also vary among years. With these failings in mind, the shooting bag data show some interesting trends.

Baines (1991) split the bag data into two regions due to differing trends; the central Highlands (9 estates) and Tayside (13 estates). The Tayside data show a fluctuating upward trend from 1880 until about 1922 (Figure 1b). Thereafter the population appears to have declined until about 1942 after which it stayed at a relatively low level until the 1950s. A small recovery appears to have occurred during the 1960s and part of the 1970s, but only to crash again in the late 1970s.

The colonisation of the central Highlands was later than in Tayside (Figure 1b). Pennie (1951) showed that by 1879 capercaillie distribution extended no further north that the North Esk. Further releases of adults and cross fostering eggs onto black grouse eventually led to the central Highlands being colonised (Pennie, 1951; Pennie, 1950), but it was not until the 1920s that substantial numbers were being shot. Thereafter numbers increased rapidly and peaked in the late 1930s, but this was quickly followed by a dramatic crash to a very low level by the early 1940s. Numbers remained low until the late 1950s, after which a recovery occurred until the late 1970s only to be followed by another crash.

Common factors in both data sets are low numbers shot from the early 1940s until the late 1950s, higher numbers during the 1960s and throughout most of the 1970s, although in Tayside the recovery was less marked than in the central Highlands, followed by a dramatic decline from the late 1970s. Less shooting effort during the Second World War could have be one reason for the apparent decline in the early 1940s, but it does not account for the dearth of birds shot during the late 1940's and 1950s. That a decline actually occurred at this time is supported by a survey in 1948, which indicated a drop in numbers over the previous ten years and a retreat from some previously colonised areas (Pennie, 1950; Pennie, 1951). Extensive wartime felling of native pinewood appears to be one of the most plausible explanations for this decline, but this is based on anecdotal evidence and has not been fully explored.

It is remarkable that populations recovered so well after such an extended period of relatively low numbers after the war. Parslow (1973) remarked that "by 1959 numbers had begun to increase again in many areas, though locally its numbers were still depressed". During the 1960s until the mid-1970s capercaillie again flourished, but more so in the central Highlands than in Tayside. In fact, capercaillie became so numerous in some areas that control measures had to be taken to reduce damage to growing trees (Palmer, 1956; Palmer, 1976; Johnstone, 1970). Moss (1993) presented an additional set of shooting bag data from six large estates during1960-1983. These too indicate a peak in numbers around 1970 followed by a progressive decline until 1983, after which few capercaillie were shot.

The reason for this improvement is unclear, but a run of favourable weather conditions or habitat availability may have been involved. A run of warm springs in the 1960s appears to have led to higher than average breeding performance and recruitment in ptarmigan Lagopus mutus in the Cairngorms, and capercaillie could have been similarly affected (R. Moss pers. com). Combined with this run of warm springs, many of the forests planted during the 1920s and 1930s would have been open enough for capercaillie to use by the 1960s and 1970s. A comparison of forest cover (extent, species and age distribution) and climate before, during and after this period might shed more light on this interesting phase, which also occurred when gamekeeper numbers were relatively low (Figure 1c). At a finer scale, new techniques, such as the use of othorectified aerial photographs (Cameron, 2000), allow more precise estimates to be made of temporal changes in the extent and structure of native pinewoods, and other woodland types.

2.2.3 Recent quantification of range and numbers

Only recently have the range and numbers of capercaillie been more accurately quantified. The breeding distribution was mapped by two Atlas projects in 1968-72 and 1988-91 (Sharrock, 1976; Gibbons et al., 1993). The first Atlas was undertaken at the time when the shooting bag data suggested that numbers were at a post-war peak. Comparisons of the two data sets show a reduction in range of about 64% by the time of the latest Atlas. However, because of recording differences between the two Atlases such comparisons should be treated with some caution, but nevertheless a substantial range contraction was confirmed.

There is a consistent pattern between numbers and range. When populations are increasing there is an expansion in range to the north, west and south of the central Highlands. When numbers decline, range contracts to the core areas in the central Highlands. This pattern equates well with a dynamic source/sink model. Native pinewoods are mainly source habits; that is more birds are produced there than is necessary to maintain numbers. These areas export birds to sink habitats such as plantations, where the populations are not self-sustaining and are dependent on immigration. The balance between source and sink habitats is dynamic and under favourable conditions a proportion of the sink habits become source habitat and vice versa under poor conditions, such as at present.

The first attempt to estimate numbers (and range) used transect counts carried out over two consecutive winters (92/93 and 93/94) and produced an estimated population of 2200 birds (1500 - 3200, 95% confidence limits) (Catt et al., 1998). Based on the work of Catt et al. (1998), the Forestry Commission's Highland Conservancy has produced a map showing the most important areas for capercaillie (Figure 2). This zonation provides one way of more effectively targeting conservation effort on capercaillie (sections 3 & 4).

A similar survey was repeated in the winter of 1998/99 and produced an estimated population of 1073 birds (549 - 2041, 95% confidence limits) (Wilkinson et al., 1999). Thus based on the mean figures, a decline of 51% is indicated between the two periods, which highlights the present precarious nature of capercaillie in Scotland. Currently, the species is confined to scattered areas with the valleys of the Spey, Findhorn and Dee, with isolated populations on the Black Isle and in Easter Ross (Wilkinson et al., 1999) (Figure 2). There are a few exceptions to this general pattern. One of the most notable is a small population that has persisted on the islands of Loch Lomond throughout the latest downturn in numbers (Waltho, 1999). Here numbers have fluctuated, but there has been no overall downward trend as with most other populations.

2.3 Habitat and diet of adults in winter

2.3.1 Methods of describing habitat

The method most widely used in Scotland to quantify capercaillie habitat is that devised by Picozzi et al. (1992) and Moss & Picozzi (1994). This uses a key to allocate woodlands to one of 28 stand type boxes derived from a principal component (PC) analysis of woodlands with varying numbers of males at capercaillie leks. The position of each box on the grid is determined from the first two PC scores. The "granny" score (first axis) describes the naturalness of a stand; many open semi-natural pinewoods have a high granny score. The "plantation" score (second axis) describes features common in plantations, such as tall, closely spaced trees with little ground vegetation. In addition, both axes are related to succession; young stands have low scores and old stands have high scores. The method has been used in studies that have looked at relationships between aspects of capercaillie ecology and woodland structure (Wilkinson et al., 1999; Catt et al., 1998) or woodland structure alone (Summers et al., 1999), and deserves to be more widely used.

2.3.3 Habitat use

Capercaillie are birds of extensive old forests, particularly of coniferous species. Their world range coincides more closely with the distribution of Scots pine Pinus sylvestris and Norway spruce Picea abies than with other tree species, although firs Abies spp., larches Larix spp. and other species of pine occur in part of their range (Cramp & Simmons, 1980; Klaus et al., 1989). Occasionally capercaillie are present in more varied forests, some of which comprise a high proportion of broadleaved trees, such as oak Quercus (Castroviejo, 1970; Castroviejo, 1975). Most forests with capercaillie grow on acidic soils where ericaceous scrubs, bryophytes and lichens form a large part of the ground vegetation. Blaeberry Vaccinium myrtillus is a key species (see later), and is a consistent component of the ground vegetation of forests throughout the world range of capercaillie.

Habitats occupied by capercaillie in Scotland in winter fit into the overall pattern found throughout their world range. Typically they are birds of old forests, such as semi-natural pinewoods, but they will occasionally also use old woodlands of other species, such as Sitka spruce (Picozzi et al., 1996). However, during periods of low populations, such as at present, it is semi-natural pinewoods in the central Highlands that retain the best population while other habitats outwith these core areas are largely vacated or have low density populations (Wilkinson et al., 1999). In contrast, during periods when populations are thriving they colonise other coniferous habitat outwith the core areas. These are mainly plantations of Scots pine, but also of introduced conifers, particularly when patches of old trees are present.

2.3.2 Diet

Adult capercaillie are almost exclusively herbivorous, and well adapted to the severe winter conditions that are prevalent throughout most of their range (Cramp & Simmons, 1980; Glutz von Blotzheim et al., 1973; Andreev & Lindén, 1994; Andreev, 1988). Not surprisingly they exhibit seasonal differences in diet because many potential food plants are covered by deep snow during winter (Pulliainen, 1979; Pulliainen, 1970). At this time of the year they feed mainly in tree foliage and only switch to feed on ground vegetation once the snow melts. A progressive move back towards feeding in trees happens as snow accumulates in early winter (November and December) (Zwickel, 1966). This foraging pattern persists in areas or years with little snow.

To some extent winter diet reflects the forest type used by capercaillie, but some tree species are apparently browsed in preference to others. The needles, buds, twigs and immature cones of Scots pine can comprise almost their entire diet in Fennoscandia where Scots pine is abundant (Pulliainen, 1979; Pulliainen, 1970; Seiskari, 1962). They also appear able to select trees with a lower than average resin content and higher than average nitrogen content, thus maximising their protein intake (Pulliainen, 1970; Spidsø & Korsmo, 1994; Lindén, 1984). Norway spruce is eaten much less frequently, even though it may be abundant in the same locality. This apparent preference for pine may to some extent be related to canopy structure rather than an aversion to eating spruce.

Capercaillie are large birds with hens weighing just under 2 kg and males around 4 kg (Cramp & Simmons, 1980). Many old Scots pine have crowns that enable birds to move throughout by a network of substantial branches, which facilitate browsing. The "granny" trees of semi-natural pinewoods in Scotland are a good examples (Steven & Carlisle, 1959). In contrast, crowns of Norway spruce are more conical with relatively fine branches, making them less suitable for a large bird to forage in. This difficulty is exaggerated in many alpine and northern provenances of Norway spruce, which have very narrow crowns with semi-pendulous branches, an adaptation for snow shedding. Occasionally capercaillie will feed heavily on young Norway spruce, and in times when numbers are high substantial browsing damage can occur (Bjor, 1959). The smaller female is able to feed in trees with lighter crowns and in stands with higher tree densities.

Winter diet can be quite different outwith Fennoscandia. In the Cantabrian Mountains where capercaillie live in oak forests, holly Ilex aquifolium is the most important winter food (Castroviejo, 1975; Castroviejo, 1970). In the Jura Mountains, silver fir Abies alba foliage and beech Fagus sylvatica buds comprise around 90% of the diet, with Norway spruce and blaeberry making up the balance (Gehringer, 1978).

There are three studies of diet in Scotland (Zwickel, 1966; Picozzi et al., 1996; Jones, 1982). Zwickel (1966) examined the crop content of 99 birds from north-east Scotland, which had been shot between October 1965 and January 1956 (Table 1). The overall contents of their crops comprised 93% conifer needles, buds, twigs and cones. Scots pine was by far the most abundant species eaten (90%) followed by a much smaller amount of Douglas fir Pseudotsuga menziesii (3%). Cereal grains comprised the balance (6%). Traces of Norway spruce, Sitka spruce and European larch Larix decidua were also found in some crops, as were traces of numerous ground vegetation plants. Jones's (1982) study was carried out just over ten years later (Table 1). Scots pine was again taken more frequently than any other food, but substantially more Sitka spruce Picea sitchensis , blaeberry and heather Calluna vulgaris was eaten. This sample of crops was mostly from birds killed in winter, but included a few from other months. Nevertheless, Jones (1982) stated that when winter crops were analysed separately they still contained similar amount of dwarf shrub vegetation.

The latest study of winter diet was from an unusual habitat where capercaillie inhabited four adjacent blocks of forest in Perthshire in which Sitka spruce was the most abundant tree species (Picozzi et al., 1996). Faecal pellets were analysed to determine diet. Sitka spruce comprised over 70% of winter diet with most of the balance made up with Scots pine. Some birds were radio-tagged and these often used the older patches of Sitka spruce, especially those with windblown pockets. Many blown trees were still alive and sprouting new shoots. Presumably capercaillie found it easy to walk along the nearly horizontal trunks and browse the new shoots. Such patches also provide good cover from potential predators. Thus, all three Scottish studies confirm the importance of tree canopy feeding by adults in winter.

2.4 Habitat and diet of adults during spring - autumn

2.4.1 Habitat use

The relationship between semi-natural pinewoods and capercaillie density in Scotland is largely derived from winter count data (Wilkinson et al., 1999; Catt et al., 1998), which is not the crucial time of the year (2.3). Unfortunately there is no comparable data for spring and early summer, when the quality and availability of foraging areas for females and broods are more likely to have a limiting effect on populations through numbers of chicks reared. This is not to say that semi-natural pinewoods are not important in spring and summer, but raises the point that other habits may be important too. For example, old open woodland is likely to have more heather and less blaeberry than younger stands of trees. Thus, it may be essential to have a mix of young and old crops rather than a dominance of old forest in the landscape. Studies elsewhere have shown that capercaillie use different habits or even different areas in different seasons (Storch, 1995a) and in Perthshire a population inhabiting a spruce dominated forest made greater use of younger stands and clear cuts in summer than in winter (Picozzi et al., 1995). This shift in habitat preference between seasons largely results from changes in diet.

2.4.2 Diet

Diet from spring through to autumn is more varied than during winter. This is because capercaillie sequentially exploit seasonally available plant foods (Cramp & Simmons, 1980; Semenov-Tian-Shanskii, 1959; Jacob, 1987). These are mostly eaten on the ground, although there is a gradual progression from tree to ground feeding in spring and the reverse in autumn. This slow change from one food to another allows time for the gut to adapt to a different diet (Moss & Hanssen, 1980).

During the spring transition from tree to ground feeding, young tree shoots are frequently eaten (Borchtchevski, 1994; Picozzi et al., 1996; Pulliainen & Tunkkari, 1991; Rolstad, 1988; Storch et al., 1991; Jacob, 1987). Larch seems to be particularly palatable at this time of the year, as are the flower buds of numerous conifer species, which have a relatively high protein content. The buds and new shoots of broadleaved trees are also eaten, particularly from aspen Populus tremula , rowan Sorbus aucuparia , and beech. Aspen seems to be sought after in some localities (Rolstad, 1988), as are newly emergent flower heads of cotton grass Eriophorum vaginatum, flower buds of birch and shoots of Equisetum spp. (Pulliainen & Tunkkari, 1991). Females exploit these nutrition food more than males.

Once ground feeding is established, shoots and stems of ericaceous plants are an important part of the diet, being eaten throughout late spring, summer and early autumn. Blaeberry is one of the most important of these dwarf shrubs. A wide range of additional foods are eaten in spring, including the young curled shoots of bracken Pteridium aquilinum and ferns, capsules of mosses, woodrush Luzula spp. and a variety of herbaceous plants. In summer the seed heads of sedges Carex spp. and rushes Juncus spp. are eaten, as well as some invertebrates. Later on, berries of Vaccinium spp. and Rubus spp. provide an extra bonus prior to the onset of winter. Deciduous tree shoots (e.g. larch and aspen) are frequently eaten in the autumn before leaf fall and the move towards feeding on evergreen conifers for the winter (Rolstad, 1988; Picozzi et al., 1996; Seiskari & Koskimies, 1955). In late summer/early autumn juveniles are still growing, especially the larger males, and these appear to select for higher quality foods than adults (Pulliainen, 1979).

The only dietary study of adults in Scotland was undertaken in a spruce-dominated forest in Perthshire (Picozzi et al., 1996). Sitka spruce still provided a substantial portion of their diet in spring, summer and autumn, although not as much as in winter. More larch was eaten in these seasons too, particularly in spring and autumn. Interestingly, the fruiting heads of sedges were one of the most important food in summer. Sedges were abundant on clear cuts and radio-tagged birds were known to feed there. Surprisingly, dwarf shrubs featured little in the diet at any season, but they were relatively scarce in the environment.

Food availability for adults throughout most of this period is probably not limited, apart possibly with females just prior to breeding. In April the quality of food available to hens may be crucial in determining breeding success (Moss & Hanssen, 1980; Moss et al., Submitted). At this time they need foods with relatively a high nitrogen and phosphorus content, which can be provided in the young shoots and flower buds of trees and dwarf shrubs and the newly emergent flower heads of cotton grass. However, relatively little is known about hen diet at this time of the year (Pulliainen & Tunkkari, 1991).

2.5 Chick diet and brood habitat

2.5.1 diet

In contrast to adults, young chicks are very dependent on insects. A number of studies have shown that arthropods can comprise over 50% of chick diet during the first few weeks after hatching (Kastdalen & Wegge, 1985; Spidsø & Stuen, 1988; Rajala, 1959). A protein-rich diet appears to be essential for sustaining the rapid growth of young chicks. The range of insects eaten by chicks is large and varies from study to study. Some of the most important families include Hemiptera, Coleoptera, Lepidoptera (larvae), Diptera and Hymenoptera (Spidsø & Stuen, 1988). Ants (mainly smaller species, not wood ants) and spiders are also eaten. However, some of most important insect foods are the larvae of sawflies and geometrid moths that are particularly abundant on blaeberry (Atlegrim & Sjöberg, 1995).

In Norway, Spidsø & Stuen (1988) used imprinted chicks to investigate diet. They showed that the proportion of insects eaten was high and relatively constant over the first four weeks of life, but by the time the chicks were seven-weeks-old the diet was mainly vegetarian. In this study, the most frequently eaten plant foods by 1-4 week old chicks were flowers from cross-leaved heath Erica tetralix and common cow-wheat Melampyrum pratense. By the time the chicks were 5-7 weeks old they were mainly eating berries from Vaccinium spp, particularly blaeberry. The only study in Scotland, showed that larvae of winter moths Operophtera brumata were the main invertebrate food of chicks (Picozzi et al., 1999). In agreement with the Norwegian study, chicks ate arthropods at a fairly constant rate for about three weeks, but then declined to a low level by six weeks of age. More larvae were eaten initially and latterly more ants and spiders. Chicks that ate more larvae survived better, but larval abundance was not related to breeding success although larval size was. The main plant foods up to 20 days of age were the leaves and shoots of blaeberry and heather. After 20 days of age the fruiting heads of sedges were eaten more frequently, but diet varied between locations and also included blaeberry and heather shoots, new shoots of Sitka spruce, bracken and fern fronds.

2.5.2 Brood habitats

It is clear from the foregoing account that hens need to locate arthropod-rich areas for newly-hatched chicks. One of the main brood habitats throughout Europe is old woodland, often with a blaeberry field layer, where lepidopterous larvae and other arthropods are abundant by the time that chicks hatch in early June. In Scandinavia it is often the wetter woodlands that provide the best brood habitats, and this is where Norway spruce grows naturally (Sjöberg, 1996). In one study in Scotland, broods were shown to use clear cuts, which were on gleyed soils with quite dense vegetation, where arthropods were presumably abundant (Picozzi et al., 1995). Drier woodlands of Scots pine, which lack blaeberry, often have fewer arthropods. Børset & Krafft (1973) showed that in a predominantly spruce forest in Norway, broods mainly used the older part of the forest, not all of which contained blaeberry, but all occurred on relatively rich site types that favoured arthropods.

in Scotland, the abundance of suitable arthropods reaches a peak soon after the main hatching period in early June (Baines et al., 1996). Picozzi et al. (1999) also sampled arthropods by sweep netting in blaeberry along fixed transects in June for six years (1991-96) in Glen Tanar Deeside and showed that Geometrid larvae accounted for most of the netted samples. Interestingly, larval abundance, size and timing differed among sites, and sites with the most larvae also differed from year to year. The implication of this result is that it may not be practical to assess the quality of brood habitats by sampling invertebrates in only one or two years.

A number of factors determine the quality of vegetation and associated arthropod communities. One of the most important is the impact of grazing. Baines & Sage (1994) looked at the impact of red deer grazing on arthropod abundance in matched pairs of plots (with and without deer) in native pinewoods extending from the west to the east of Scotland. They found an east/west gradient of abundance in lepidopterous larvae, one of the most abundant arthropod groups. There was a 12-fold difference in abundance between Deeside and Argyll, with more larvae in the east. Intestingly, grazing seemed to reduce the biomass of blaeberry by half but larval abundance almost 4-fold. A predictive model indicated 5 red deer km^-2 would result in a 41% reduction in larval densities. This is a relatively low deer density, and to maximise blaeberry cover and larval abundance deer would have to be maintained below 5 km^-2 in stands with 200-300 trees ha^-1. Due to the great variation among years in arthropod abundance these results from a two-year study should be treated with some caution (see Picozzi et al., 1999). Even so, a low level of deer grazing may initially be beneficial because they make larvae more visible to chicks, but in the longer-term heather may replace blaeberry (2.5.3). Apart from the study of Baines et al. (1994) relatively little is known about how grazing influences blaeberry cover and the abundance of invertebrates, or the ability of broods to exploit them.

2.5.3 Managing brood habitats

Blaeberry is one of the key plants to encourage in brood habitats because of its associated invertebrates. In addition, its foliage, stems and berries provide important foods for adults and older chicks (Storch, 1993; Storch, 1995b; Selås, 2000). Not surprisingly, blaeberry is also utilised by many other herbivores including bank voles, hares, other grouse species, deer and sheep. Blaeberry is a long-lived rhizomatous woodland shrub that prefers well -drained acid soils. It persists through the early thicket stage in Scots pine plantations, but flourishes once tree density starts to decrease due to thinning or tree death. It declines in abundance in old open stands where it is gradually replaced by heather as more light reaches the forest floor (Moss & Picozzi, 1994; Welch et al., 1994; Hester et al., 1991; Humphrey, in press; Humphrey, 1996). Thus it often reaches its optimum growth in middle aged stands, but this can be modified by grazing and burning regimes.

In open, semi-natural pinewoods there appear to be two problems. In woodlands with heavy grazing pressure (mainly deer, but sometimes by sheep as well) there is often quite a lot of blaeberry, but in common with the rest of the vegetation it is short and offers little shelter for broods, and arthropods are scarce. In contrast, excluding deer by fencing or by reducing densities through culling results in the vegetation becoming increasingly long and dominated by heather. In addition to the loss of blaeberry, young chicks appear to find it difficult to manoeuvre in such tall vegetation. Therefore, it may be undesirable to just "let nature take it course", as heather is likely to become more dominant as the nutrient status of sites decline and stands become more open. Consideration needs to be given to how the ground vegetation can be better managed in these stands, including management options that will increase nutrient cycling and in so doing lead to a revival of blaeberry and provide better access and foraging for broods.

There are three techniques for managing ground vegetation that warrant investigation. These are controlled burning, tractor mounted swiping and cattle grazing. Burning to create small linked patches would encourage blaeberry regeneration and other nutrient-rich plant foods on the burnt areas. However, it would need to be confined to the more open areas and would have to be carefully controlled. Swiping would have a similar effect, but regrowth would probably be less nutritious than following burning. It would be easier to manage and could be done in open woodland, but tractor access would be limited by terrain. Both techniques would create mosaics of long and short vegetation that would provide access, food and shelter for chicks. Cattle grazing in winter would reduce the volume of coarse vegetation and dung would enrich sites. The openness of many ancient pinewoods is probably due to cattle grazing in the past (Dennis, 1998). However, successful cattle grazing is difficult to manage, may require fencing and may not produce the intricate mosaics of different vegetation heights that can be achieved with burning and swiping. Burning has an advantage over the other two techniques in that it is more likely to encourage tree regeneration, which in turn will shade out heather and encourage blaeberry.

There is also anecdotal evidence to suggest that broods often use younger woodlands soon after thinning or group felling, when brash covers the ground (R. Moss & D. Baines pers. comm.). It is far from clear why such areas seem to be preferred, and this aspect warrants further investigation. There are a number of possibilities; brash could have large numbers of associated arthropods, the breakdown of dead wood might enhance the nutrient status of the ground vegetation and result in more arthropods or brash may provide good cover from predators.

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