Daily energy expenditure of free-living male Wood Mice in different habitats and seasons

1. The daily energy expenditure of free-living adult male Wood Mice, Apodemus sylvaticus, from deciduous woodland and maritime sand-dune was estimated using the doubly labelled water (DLW) technique and time-energy budget models.

2. Method of calculation had a small effect on the calculated energy demands. There were no significant differences in energy expenditure across sites or seasons despite large differences in home range among mice from different sites. Mice in winter, and on the sand-dunes, had lower body masses, which offset the effects of larger home ranges and colder temperatures.

3. The daily energy expenditure for a Wood Mouse of mean body mass (20.5 g) was 67.9 kJ day(-1) (n = 19) This was comparable to other similar size rodents (slightly higher), and did not deviate significantly from allometric predictions.

4. Variation in daily energy expenditure among individuals was not explained by ambient temperature, home range size, body mass, change in body mass, time spent active and the distance or speed of travel.

5. Sustainable metabolic rates approximated to five times basal metabolism and were within the range previously reported but higher than most other estimates of free-living energy demands.

6. Rates of water influx and efflux were significantly greater for Wood Mice on the sand-dunes (influx, 9.3 +/- 1.14 ml day(-1), efflux, 10.2 +/- 1.10 ml day(-1)) than for animals in the woodland (influx, 6.3 +/- 0.48 mi day(-1), efflux, 6.2 +/- 0.47 ml day(-1)). This was probably due to differences in the water content of their diets (seed in woodland and invertebrate on the sand-dunes).

7. The time-energy budget models yielded estimates of energy expenditure considerably lower than the doubly labelled water estimate. Potential reasons for this discrepancy are discussed.