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, Apodem us sylvaticus, from deciduous woodland and maritime sand-dune was estimated using the doubly labelled water (DLW) technique and time-energy budget mod els. 2. Method of calculation had a small effect on the calculated energy demand s. There were no significant differences in energy expenditure across sites or seasons despite large differences in home range among mice from differe nt sites. Mice in winter, and on the sand-dunes, had lower body masses, whi ch 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 rod ents (slightly higher), and did not deviate significantly from allometric p redictions. 4. Variation in daily energy expenditure among individuals was not explaine d 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 es timates of free-living energy demands. 6. Rates of water influx and efflux were significantly greater for Wood Mic e 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 co nsiderably lower than the doubly labelled water estimate. Potential reasons for this discrepancy are discussed.