Ecological energetics of male wood mice Apodemus sylvaticus (L.) in two contrasting habitats
It has been suggested that wood mice Apodemus sylvaticus (L.) inhabiting maritime sand-dunes in NE Scotland "work harder" (Gorman 7 Akbar 1993; p395) than those in nearby deciduous woodland. The main objective of this study was to investigate the daily energy budgets of free-living adult male A.sylvaticus from these two habitats. Live-trapping was used to compare the population dynamics and demography at the two sites. Although similar temporal fluctuations in density were found at both sites, A.sylvaticus in the woodland maintained higher densities. Body masses of wood mice were significantly heavier in the breeding compared to the non-breeding season and in the woodland compared to the sand-dunes. Apodemus sylvaticus from the woodland had lighter kidneys, longer small intestines and longer stomachs than mice from the sand-dunes. It was suggested that these variations reflected site differences in food availability and diets of the mice. Apparent absorption efficiencies of dry matter and energy for A.sylvaticus fed mealworms, wheat grain or "All-bran" diets did not differ across sites. Thus, the larger gut capacity of mice living in woodland may facilitate a faster ingestion rate, possible due to the higher food availability, while maintaining constant absorption efficiency. The heavier kidney mass and greater water flux of A.sylvaticus on the sand-dunes were probably associated with the relatively higher water content of their diet, which was dominated by invertebrates, compared to the seed diet of mice in the woodland. At the woodland site, the breeding season was associated with an increase in home range size and distance travelled relative to the non-breeding season. Although the total time spent active did not differ between seasons, diurnal activity was only exhibited during the breeding season (ca. 60 mins).