Ecological energetics of two European shrews: Crocidura russula and Sorex coronatus (Soricidae: Mammalia)

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Abstract
The energy strategies and especially the overwintering strategies of Crocidura russula (Croci‐durinae) and Sorex coronatus (Soricinae) were compared. These two species are sympatric over a large part of Europe, but have different ecological distributions and belong to subfamilies which have evolved under different climates. Energy budgets of wild animals were estimated by combining measurements of the metabolic rate in the laboratory (respirometry) with a time‐budget analysis in the field (radioactive tracking). Oxygen consumption was measured at different ambient temperatures (T,) and for three different behavioural states: activity, normothermic rest in a nest and torpor in a nest. These measurements were extrapolated for free‐living shrew populations by taking into account field data on morphology, behaviour, demography and climate, obtained in western Switzerland. If expressed by unit weight, the daily energy expenditure of S. coronatus, E (J g‐1) = 6459–89 T,(°C), is higher than the maximal expenditure of C. russula, E (J g‐l) = 4714–106 T,(°C). This is a consequence of the higher metabolic and activity rates of S. coronatus. However, since S. coronatus is a little lighter, individuals of both species have similar absolute expenditures. Unlike S. coronatus, overwintering C. russula can drastically lower their budget (up to 30% reduction) by the use of several saving mechanisms, e.g. torpor, nest huddling and selection of warm resting sites. But this species may reach high densities in winter and thus its population budgets may be high (up to 3000 kJ ha‐1 day‐1 for average winter conditions). The overwintering S. coronatus undergo a body size reduction, and their strictly territorial social organization maintains the population requirements at a low level (usually less than 500–600 kJ ha‐1 day‐1 for average winter conditions). The energy strategies of these two temperate shrews are correlated to their ecological distribution, and competition played an important rôle in their evolution.
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