The Red Squirrel (Sciurus vulgaris L.) in relation to its food resource
Tittensor, Andrew M
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1. A study of the ecology of the native red squirrel (Sciurus vulgaris leucorus) was carried out in a mature Scots pine (Pinus sylvestris) plantation in East Scotland. 2. The aims of this study were:- 1)To determine the population size, its structure, and the dispersion of squirrels in a selected area of habitat. ii) To determine qualitatively and quantitatively the food eaten by that population. iii) To relate, where possible, the population findings to the food resources. 3. Consideration of the distribution of the red squirrel led to the conclusion that there is a habitat preference for mature conifer woodland, and that the red phase of this squirrel is associated particularly with Scots pine woodland. 4. A brief literature review showed that there had been no integrated study of the population dynamics and dispersion of the red squirrel, and only preliminary attempts to relate food resources to population density. 5. The advantages and disadvantages of the red squirrel for this type of study are considered. 6. The location, history, physical features, vegetation and fauna of the study area are described. 7. Approximately 93% of the I23 hectares of woodland consisted of mature pine, 39 to 49 years old, with about 1,400 trees per hectare. A gale midway through the study caused about 25% loss of trees due to windblow. 8. The past history and present distribution of the red squirrel in Scotland are sunmarised. Its fluctuations and relations with the grey squirrel are discussed. 9. A tentative classification of known behaviour patterns of th red squirrel is given for both individual and social behaviour. Relevant features of the basic biology are also reviewed. IO. Methods for the population study included live-trapping, field observation, drey surveying, and carcase examination. 11. Most of the population parameters estimated were based on data obtained from live-trapping, so a full account of these methods is given, including trap type and dispersion, trapping procedure, sex and age determination, and marking methods. 12. The squirrel's reaction to the trap is discussed and it is concluded that sampling approximated to random. 13. The population size was relatively stable at about 100 squirrels over three years. 14. Initially the sex ratio was equal, but became biased in favour of females, corresponding to excess recruitment of females. 15. The annual increment of young was between 20% and 40% of the total population, and the minimum turnover period was 4.5 to 5 years. After a high juvenile mortality before the weaning stage life expectancy was high, with slightly higher mortality rates amongst the older age classes. 16. Immigration and emigration apparently contributed little to recruitment and losses. 17. Methods for the feeding study included field observation, analysis of stomach contents, measurement of cone production and feeding signs, assessment of bark stripping damage, and the use of captive squirrels. 18. The production cycle of Scots pine is outlined. 19. The main and subsidiary foods of red squirrels are tabulated seasonally; they depend on Scots pine for seeds, buds, shoots, pollen ard vascular tissue, as well as for nesting sites and cover. 20. An increased use of ground food was made from March to July, as tree-borne seed was reduced by seedfall. Selection of cone sizes occurred, but this only affected the availability of the cone crop marginally. 21. Both live and dead trees were barked by squirrels; the vascular tissue below the bark was eaten as a subsidiary food source. 22. About one-third of the available cones, the main food source, was utilised for seed extraction, representing an intake of 5% of the body weight per day. Little over half of the daily activity period was spent feeding. 23. The available food was apparently not limiting population size, though the short potential critical period, when the main food source was depleted, coincided with the production of young. 24. Management recommendations for the control or conservation of squirrel populations are proposed, and suggestions for future work are given.