Information and Advisory Note Number 101
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Management of red deer on Rum
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.
Stabilisation of population size 1957-1972
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
year.
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.
Effects of increasing density
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.
Comparative effects of reducing hind and stag numbers
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.
Management implications
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.
19. Further reading:
Clutton-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: behavior and
ecology of two sexes. Edinburgh University Press, Edinburgh.
20. 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).
21. Contact for further information
Rum red deer project:
Helen Armstrong
Uplands Group Advisory Services
Scottish Natural Heritage
2
Anderson Place
EDINBURGH
EH6 5NP
Tel: 0131-446 2476
Red deer issues in general:
Ro Scott
Uplands Group Advisory Services
Scottish Natural Heritage
27 Ardconnel
Terrace
INVERNESS
IV2 3AE
Tel: 01463 712221
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