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Individual study: Supplementary feeding increases wood mice Apodemus sylvaticus density due to better overwintered and juvenile survival, Marley Wood, Oxfordshire, England

Published source details

Flowerdew J.R. (1972) The effect of supplementary food on a population of wood mice (Apodemus sylvaticus). Journal of Animal Ecology, 41, 553-566


Earlier studies in Oxfordshire, (southern England) had shown that the amount of natural food available to wood mice Apodemus sylvaticus influences their quality and survival. In this study,the food supply was artificially increased to assess the effect on over-winter survival and to see if it improved juvenile survival during the summer. The study was undertaken in a deciduous woodland, Marley Wood, on the Wytham Estate, Oxfordshire.

Wood mice were live-trapped in two triangular study plots (60 m apart at closest point). Wheat was provided at 45 live-trapping points within each. In the supplemental feeding plot (hereafter ‘wheat plot’; 1.1 ha) traps were spaced 20 m apart; in the control (1.5 ha; no supplemental food provided) traps were 23 m apart.

In the wheat plot, from 9 February 1968 to 5 December 1969, approximately 22 kg of wheat was provided at 7-10 day intervals (in wine bottles with neck removed) at each trap-point; from 21 March to 15 April 1969 no wheat was added (supplies ran out).
Trapping was undertaken from October 1967 to December 1969. Two Longworth live-traps were set at each point at about 5-week intervals (checked evening and morning). Mice caught were sexed and weighed, and female reproductive condition recorded. Individuals were marked (toe-clipping and ear-notches) and released.

Upon addition of wheat the mice in the wheat plot began to increase in weight, and in the two springs, average weights of males and females were up to 20% higher than those in the control.  In the spring of 1968, the breeding season also appeared to start at least a week earlier in the wheat plot.

At the start of the experiment mice densities on the two areas were about the same (12.8/ha in control and 9.8/ha in the wheat plot). By June 1968 densities had declined (3.6/ha in control and 6.9/ha in the fed plot) and were similar in the autumn. In early spring 1969 as breeding commenced populations again increased (11.6/ha in the control; 22.6 in the fed plot). The short interruption in wheat supply (21 March to 15 April 1969) led to a sharp decrease in numbers and survival in the wheat plot.
The higher density in the wheat plot in summer was the result of better over-winter and juvenile survival. However, there appeared to be a general upper limit to population size, (especially in summer) not governed by food supply; whilst supplementary food increased juvenile survival it only resulted in a slight increase in the number entering the population. Adult territorial aggression may be a regulatory factor. Supplementary feeding also increased immigration compared to the control.
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