A conservation framework for golden eagles: implications for their conservation and management in Scotland

Main findings

1. Occupying approximately 440 territories in 2003, the national golden eagle population of Scotland failed to meet the abundance target for favourable conservation status. Only three of sixteen regions, where eagles have occupied territories since 1982, were considered to be in favourable conservation status (Table 6). These are all in western areas: the Western Isles (Zone 3), the Western Seaboard (6), and Argyll West and Islands (14; Figures 1 and 7). A fourth region, the Northwest Seaboard (7), would have passed all tests for favourable conservation status if recent mergers of traditional golden eagle territories were taken account of.

2. The most serious failures to meet favourable conservation status tests were in NHZs in the central and eastern Highlands (the Central Highlands (10), Cairngorms Massif (11), Breadalbane and East Argyll (15), and North East Glens (12); Figures 1 and 7), where less than half of all known territories were occupied (Table 1). Based on the production of young golden eagles (Table 2), the populations in these regions should be expanding markedly, but instead they continue to decline (there was a loss of 15 occupied territories between 1992 and 2003, and 86 vacant territories by 2003; Table 1). This indicates, in the absence of any evidence for emigration, that survival of subadult and/or adult birds is low. 

3. In two regions of western Scotland, the Western Highlands (8) and Lochaber (13), unfavourable status arose because of insufficient young birds being produced (Table 2), probably because of a shortage of live prey through a possible combination of heavy grazing by deer and sheep, and excessive burning of vegetation.

4. The evidence for impacts of a number of potential constraints on golden eagles in Scotland has been assessed rigorously. These include: topography, vegetation, land cover, geology, commercial forestry, unintentional human disturbance, wind farms, expansion of white-tailed eagles, persecution, and grazing by sheep and deer. Studies of the influence of different constraints on favourable conservation status, which have been published recently in several scientific papers and reports, are summarised. Current evidence indicates that illegal persecution and low food availability in parts of western Scotland are the two main constraints on the Scottish golden eagle population.

5. A number of lines of evidence indicated that illegal persecution of eagles, principally associated with grouse moor management in the central and eastern Highlands, is the most severe constraint on Scottish golden eagles. These lines of evidence, based on population modelling and analyses using a Geographical Information System (GIS) are as follows: 

a) As carrion feeders, golden eagles are particularly vulnerable to poisoned bait. Records of the illegal use of poisoned baits were significantly associated with grouse moors; both nationally and within those regions where grouse moors predominated as a land-use (Figure 5). There was no evidence of a decline in records of poisoning on grouse moors between 1981 and 2000, even though poisoning incidents had declined in upland areas away from grouse moors;

b) Records of illegal persecution of golden eagles (including poisoning, trapping, shooting) were also more common in those regions where grouse moor management predominated;

c) There was no consistent or strong evidence of associations between territory vacancies and constraints other than persecution in these regions; 

d) Persecution (assessed on the basis of the distribution of poisoning incidents) was associated with a lowering in the age of first breeding, a greater number of territory vacancies, and the use of territories by non-breeding immature eagles. The evidence indicates that persecution was reducing survival, constraining the distribution, and was probably creating ecological ‘traps’ by attracting dispersing immature eagles into areas of apparently suitable habitat that were unoccupied because previous residents had been killed. As well as affecting young birds from local nests, subadult (pre-breeding) survival in golden eagles from persecution-free areas would be reduced if they entered regions with persecution;

e) Observations of the age of birds and breeding success of Scottish golden eagles occupying territories in the 1982 and 1992 surveys were used to estimate population parameters (survival and productivity) in the different regions of Scotland. Age structure estimates of adult survival suggested that regions where persecution was most common suffered the greatest shortfalls in the numbers of adults. Regional differences in age structure associated with differences in the intensity of persecution (density of poisoning incidents) were used to adjust demographic estimates to simulate the absence of persecution. iv In the absence of the estimated 3 – 5% decrease in national adult survival rates associated with persecution, population modelling suggested the Scottish golden eagle population would increase. Estimates that are not adjusted to simulate a ‘no-persecution’ scenario, however, suggested that the Scottish golden eagle population was vulnerable to decline. In golden eagles, a species which is naturally long-lived, even slight changes in adult and subadult survival rates can have major population consequences;

f) Population modelling based on breeding productivity and recent population trends indicated that too many birds were dying in those regions where grouse moor predominated, and this would not maintain the breeding population. For the Central Highlands (Zone 10) the Cairngorms Massif (11) and Breadalbane and East Argyll (15), population simulations using the 1992 and 2003 surveys indicate that survival rates must be lower than other zones, otherwise the golden eagle populations in these areas would be expected to expand due to high productivity (Table 2). In the Cairngorms Massif (11), for example, as few as 10% of subadult eagles may survive to breed. These low survival rates are inconsistent with the apparently considerable resources of food and space for eagles in these regions, but are consistent with eagles being killed, as suggested by other lines of evidence; and

g) Analysis of change in occupied territories between the 1992 and 2003 national surveys in relation to a number of potential constraints (including grazing, recreation, incidental disturbance and afforestation) found no strong evidence for the influence of any constraints other than persecution. The four NHZs (10, 11, 12 and 15) where persecution indices had not changed or increased were also those where grouse moor management is most common. Eagles in these areas showed a 21% decline (70 pairs (active territories) in 1992 down to 55 in 2003; Table 1). The only two regions with marked increases in occupied territories in 2003 (3 and 5; Table 1) were two of the three regions which experienced a decline in persecution indices. Occupied golden eagle territories therefore tended to decline where persecution was probably still influential, but to increase where persecution had probably declined. Overall, had there not been population increases in two regions where persecution had declined, the national Scottish population would have declined in 2003.

6. The highest national priority for the conservation and management of golden eagles in Scotland is to tackle persecution in those areas where it still persists. A secondary national priority for restorative management is to promote greater availability of live prey in parts of the western Highlands, potentially through changes in the management of deer and sheep. A number of studies have shown a positive link between the abundance of live prey and breeding success, although further research on the interactions between deer and sheep grazing and golden eagle ecology would be beneficial due to their complexity.

7. Golden eagles, and the constraints which appear to influence them, should continue to be monitored. Potential constraints which may be deserving of more attention in the future would include the potential decreased availability of sheep and deer carrion and the extensive culling of mountain hares on some Highland grouse moor estates. Throughout its breeding range, from the arctic to northern Africa, the golden eagle has successfully adapted to a wide range of climatic conditions, but further attention to the potential implications of climate change for the Scottish population would be beneficial. Key enhancements to monitoring will be gained by surveillance of adult survival through fingerprinting of DNA from cast feathers and monitoring dispersing, pre-breeding birds using remote telemetry.