Information and Advisory Note Number 101 Back to menu
1. Since 1958, the red deer population of Rum (which was initially purchased by
the Nature Conservancy in 1957) has been used to investigate the effects of
different management regimes on red deer populations.
2. There is no record of whether red deer occur naturally on Rum or whether they were originally introduced by man. Their numbers on the island have been closely related to the size of the human population. In the 16th century they were evidently common, but in the 18th century the human population of the island grew rapidly and, by 1772, only 80 deer were left, and the deer population became extinct in about 1787. Around 1845 the island was again restocked with red deer, and by 1895 their numbers had increased to 800. Between 1845 and 1957 the island was managed as a sheep walk and sporting estate. Numbers of sheep varied but were commonly in excess of 3,000 during this period.
3. In 1957 the Nature Conservancy purchased Rum from the Bullough family and removed the entire sheep population (then 1,750 animals). The first systematic deer count on Rum in 1957 gave a total of 1,584 animals.
4. Since 1957, the island has been divided into five blocks for culling purposes (see Figure 1) that are culled in proportion to the number of deer counted in them during the spring counts. Following traditional practice, stags are culled mostly in July, August and September, hinds in November, December, and January. On most measures of performance, the Rum red deer population falls close to the average for other Highland populations (see Information and Advisory Note 100).
Figure 1: Map of Rum showing the deer management Blocks. Dotted lines show the routes taken in regular census of the island designed to measure changes in habitat use and population distribution.
5. After the Nature Conservancy took possession of Rum in 1957, the annual cull
was raised from approximately 6% to around 15% of the population in spring.
Culling at 14-16% prevented deer numbers from rising despite the removal of the
sheep population. Though calculations suggested that the population would
sustain an annual cull of 17%, in practice, numbers have fallen after culling
levels exceeded 14%. Between 1977 and 1986, when wet autumns and cold winters
reduced recruitment, the hind population could only sustain a cull of 11% per
Following the removal of sheep, deer numbers (animals ≥ 1 year) increased from 1,584 in 1957, to 1,800 in 1960. Since then, they have remained between 1,830 and 1,175 animals.
Figure 2. Changes in the population size of stags and hinds ≥ 1 year old on Rum, 1958-1965, in years following culls of different sizes.
6. Reduction of grazing pressure following the removal of sheep, and the cessation of burning of heather-dominated areas, was associated with an increase in the cover of Molinia and Calluna in the wet heath, an increase in Molinia cover in the Schoenus fen, and a possible reduction in
species diversity in the species-poor Agrostis/Festuca grassland.
7. In 1972, the annual cull in the North Block (Block 4) of Rum was terminated
in order to investigate the effects of increasing density. Prior to 1972, the
block supported around 250 deer with a sex ratio of approximately 2 stags per
hind and a calf/hind ratio of around 50%.
8. After the cull was terminated, hind numbers increased rapidly until 1980 and then increased more slowly, showing larger fluctuations between years (Figure 3). Stag numbers in the block declined after 1977, stabilising after 1981. By the 1990s, the block supported more than twice as many hinds as stags.
Figure 3.: Numbers of hinds and stags k 1 year old resident in the North Block of Rum 1971-1990.
9. Increasing deer density was associated with a reduction in survival among calves and yearlings but with little change in adult survival. In all age categories, males showed lower survival rates than females and rising density depressed the survival of male yearlings more than females (Figure 3). As hind density rose, the survival of males during their first two years of life fell from around 90% to around 40% while the survival of females fell from 90% to around 70%.
10. Increased density also reduced the fecundity of females. On Rum, females do not conceive in their first or second year of life. The proportion conceiving as two year olds and calving as three year olds fell from around 60% to less than 10%; the proportion of milk hinds (animals that raised a calf through the previous summer) bearing calves fell from over 80% to around 20% and calf/hind ratios in spring fell from around 0.45 to around 0.20. Average dates of conception changed from around October 10 to October 25, contributing to increases in calf mortality. These changes were presumably caused by a deterioration in female growth and body condition, which was reflected in later dates of coat change. However, despite the effects of increased density in Block 4, most indices of performance (including calving rates) remained higher than in other parts of the island.
11. Rising density also affected the growth of males. Average weight of antlers fell by around 20%. The length of antlers on yearlings provided a particularly sensitive index of the effects of rising density, falling from an average of 15 cm to less than 2 cm in the first ten years.
12. Rising hind numbers were associated with an increase in the proportion of time spent grazing on Agrostis/Festuca and herb-rich communities. Rising density also led to reduced use by stags of areas used heavily by hinds and increased use by hinds of areas previously used mostly by stags.
13. Population density had little effect on dispersal among hinds though, as population density increased, peripheral groups ranged more widely. The proportion of stags emigrating increased while the number immigrating into the population fell.
Figure 4:. Effects of population density on the survival and fecundity of red deer in the North Block of Rum, 1972-1990. Open symbols and dotted lines represent values for males; closed symbols and solid lines, values for females. (A) Changes in survival of calves. (B) Changes in the survival of yearlings. (C) Changes in the survival of adults (>24 months old). (D)
Changes in the proportion of hinds that successfully give birth at approximately 3 years. (E) Changes in the proportion of milk hinds calving. (F) Changes in the recruitment of calves the following season per female surviving the winter. Milk hinds are those that successfully reared a calf the previous year. Measures of reproduction and survival are plotted against female density (adults and yearlings) since the sexes are extensively segregated.
14. Both comparisons across Scottish populations and detailed research on Rum
suggest that where hind populations are not controlled by culling, the adult sex
ratio becomes biased towards females, reducing the number of males that can be
harvested each year. This result has important implication for red deer
management since it indicates that by raising hind culls, managers may be able
to increase their yield of mature males.
15. To determine whether high hind numbers reduce the performance and density of stags, an NCC committee including representatives from the Red Deer Commission and the Cambridge-based Rum red deer project, decided to instigate different culling regimes in the five blocks of Rum
• to reduce hind numbers by around two-thirds in Block 3, keeping stag culls at their existing levels.
• to reduce stag numbers in Block 1 by around two-thirds, maintaining hind culls at their existing level.
• to monitor the effects by regular census of the island's population throughout the year.
16. Experimental culling began in 1991. Hind numbers were successfully reduced by around 50% in Block 3 by 1993, while stag numbers declined more slowly and were only reduced by a similar proportion in 1995. This was apparently because the removal of stags caused rapid replacement from neighbouring populations.
• The experiment will not be complete until 2001, when it will be possible to compare measures of performance, survival and habitat use for 7 years after populations were reduced with similar values for 1981 -1991. However, preliminary analysis of changes since 1993 indicate that reduction of hinds in Block 3 has been associated with
• significant increases in the number of stags using Block 3.
• increases in the body weight of stags culled from Block 3.
• earlier dates of antler casting, antler cleaning and coat change relative to Block 2 where a 15% cull of both sexes has been continued.
• an increase in the use of short, herb-rich communities by both sexes.
18. Research based on Rum provides a
basis for predicting the effects of different
management regimes on other Highland
deer populations. In particular, it
emphasizes the importance of controlling
hind numbers in order to maximise the
annual yield of mature stags. High hind
numbers reduce male survival and growth
and increase emigration rates by males,
lowering the number of mature males that
can be culled each year. Where females
are subjected to lower annual culling rates
than males (a common situation for red
deer populations in Scotland), increasing
the proportion of females culled can lead to a substantial increase in the number of mature males in the population as a result of improvements in male survival.
Clutton-Brock, T.H. & Albon, S.D. (1989). Red deer in the Highlands. Blackwells,
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: behavior and ecology of two sexes. Edinburgh University Press, Edinburgh.
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).
Rum red deer project:
Uplands Group Advisory Services
Scottish Natural Heritage
2 Anderson Place
Tel: 0131-446 2476
Red deer issues in general:
Uplands Group Advisory Services
Scottish Natural Heritage
27 Ardconnel Terrace
Tel: 01463 712221
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