Information and Advisory Note No.100 Back to menu
1. Red deer (Cervus alphas) populations occur throughout the Highlands at densities ranging from less than one animal per square kilometre to over 30 per square kilometre. Numbers of deer on the open hill are thought to have been around 155,000 in the late 1960's. By the mid seventies, numbers had risen to around 248,000 while by the late1980's they had increased to around 300,000. It is not clear whether numbers have changed significantly during the 1990s.
2. The rise in deer numbers in the 1970s was probably partly caused by climatic changes Between 1967 and 1975 the average duration of winter snow cover was unusually short. Over the same period, summer rainfall declined and summer temperatures increased. Warm, dry summers are associated with increased production of heather, the principal winter food of deer in many areas, and may also have contributed to the rise in deer numbers.
3. Changes in sheep stocks may also have been involved. Sheep numbers in the Highlands were relatively high in the early sixties but declined steadily between 1966 and 1979, before rising again after 1980. Sheep and red deer (especially hinds) prefer similar areas of habitat and local reductions in sheep numbers are commonly associated with subsequent increases in deer numbers.
4. A third possible factor in the increase in red deer numbers may have been the increase in afforestation. The extra shelter provided by plantations to which red deer have access is likely to have increased their winter survival rates.
5. Deer density varies widely between regions. The highest deer densities, of more than 20 deer per square kilometre, are found in the Central Highlands and some of the islands off the west coast while the lowest deer densities (of between 5.0 and 10.0 deer per square kilometre) are found around the edge of the deer range to the south and east.
6. Both differences in habitat quality and differences in management regimes contribute to variation in deer density. High densities of deer occur where deer have access to low ground or woodland, while low densities occur where sheep density or culling rates are high. Stag density (but not hind density) declines in areas where snow cover is usually prolonged for every 25 day increase in average snow cover per year, stag density declines by approximately 1 stag per square kilometre. Hind density (but not stag density) declines with increasing sheep numbers.
7. During the 1970's and 1980's, hind culls in many areas of the Highlands were substantially below the level necessary to control hind numbers. Though culling rates have increased in recent years, many deer estates could probably still increase their annual income by lowering the density of hinds. Reductions in hind density would also serve to reduce the rate of heather loss and increase the chances of successful tree regeneration.
8. Red deer populations generate important economic benefits The total reported annual cull is currently between 55,000 and 65,000 animals, generating substantial income from the sale of venison (and other deer parts), as well as from sporting lets and supporting a substantial number of jobs. As would be expected, the deer-related income from estates increases in relation to the number of animals that can be culled each year.
9. Grazing is also an important component of the management of upland plant communities, and can help to maintain a wide array of plant species, to check the spread of a few dominant plants and to stimulate the production of accessible growth by dwarf shrubs. However, very heavy grazing pressure by deer and by domestic stock can depress the production of heavily used grasses in spring and can cause a reduction in cover of heather and other dwarf shrubs. Sheep, which are commonly maintained at densities of 40-60 per square kilometre, have similar effects on the habitat and, in many areas of the Highlands, their influence may be more important than that of deer.
10. Even moderate deer densities can retard or prevent the regeneration of trees. Research at Glenfeshie shows that birch, being deciduous, is eaten largely in summer while pine shows less seasonal variation. As might be expected, damage to saplings increases with the density of deer: at 25 deer per square kilometre, few saplings of birch, larch or pine live beyond 10 years and all are dwarfed, while at 4 deer per square kilometre some saplings develop into trees At winter densities of below 2 deer per square kilometre, relatively little damage to saplings occurs. However, damage to growing seedlings is variable and is affected by a variety of other factors, including the distribution of deer and the availability of other sources of browse. The comparative effects of sheep and deer on tree regeneration are still unknown.
11. Since deer numbers affect both the economic yield of deer populations and their impact on their environment, there has been substantial interest in the consequences of maintaining deer. The dynamics of red deer populations have now been investigated in five different sites, which range in density from less than 4 to over 34 deer per kmē (Table 1).
12. Comparisons between populations confound the effects of differences in density with those of differences in habitat quality or management. High density populations may either be living on high quality ground or may be lightly culled, while low density populations may either be on poor habitat or may be heavily culled. Consequently, studies of the same population at different densities provide more precise estimates of the effects of changing numbers Relatively few studies have been in a position to investigate the effects of changing density within the same population. However, long-term studies on Rum show that high deer densities depress calving rates, increase the average age of first conception from two to three and raise winter mortality. In addition, in high density populations, the adult sex ratio tends to be biased towards hinds.
13. Further reading
Glutton-Brock, T H & Albon, S D (1989)
Red deer in the Highlands
Blackwells, Oxford
Clutton-Brock, T H & Lonergan, M
(1994) Culling regimes and sex ratio
biases in Highland deer,
Journal of Applied Ecology 31, 521-527
Clutton-Brock, T H , Guinness, F. E. &
Albon, S D (1982). Red deer: behaviour
and ecology of two sexes. Edinburgh
University Press, Edinburgh
14. Author
Professor T H Clutton-Brock (with
acknowledgements to Scottish Natural
Heritage, the Deer Commission for
Scotland, the Natural Environment
Research Council and members of the
Rum red deer project).
15. Contact for further information
Ro Scott
Uplands Group
Advisory Services
Scottish Natural Heritage
27 Ardconnel Terrace
INVERNESS
IV2 3AE
Tel 01463 712221