The three grazing treatments applied on the two meadows affected the population dynamics of the Common shrews markedly, and despite the overall differences in Common shrew numbers between the two meadows, high intensity grazing always resulted in significantly lower Common shrew numbers compared to both low intensity grazing and no grazing. Areas with low grazing intensity often held more Common shrews than the ungrazed control, though the overall differences in abundance were not statistically significant (Table 1). The pattern in the Common shrew trappings is very similar to that observed for field voles Microtus agrestis on the very same meadows [11]. Thus, in the low intensity grazing treatment, the potentially negative impacts of grazing livestock, such as mechanical disturbance, were apparently fully compensated for by the positive effects of livestock grazing.
The similarity in the response to grazing intensity amongst two ecologically distinct species, a rodent and an insectivore, points to a common environmental parameter as driver of the population dynamics. Schmidt et al. [11] suggested that for field voles the observed pattern was primarily due to livestock grazing creating a more heterogeneous vegetation in the low intensity grazed areas as compared to areas with high grazing intensity or no grazing, which, in case of the Common shrew, fully compensate for the potentially negative effects of grazing, such as mechanical disturbance. As for the field voles [11], vegetation cover, and, thus, risk of predation, is a probable cause of the grazing treatment effects observed on Common shrews in the two meadows [see also [8]]. Additionally, grazing may affect plant species composition, and livestock trampling may create a more heterogeneous micro-topographic environment, which, in turn, may affect the composition and availability of invertebrates. Increasing grazing intensity is generally believed to be accompanied by decreasing invertebrate abundance and species numbers [e.g. [12]]. Roberts & Morton [13], however, reported that Scarabaeidae biomass peaked an intermediate grazing intensity. Also, invertebrate species richness may benefit from low intensity grazing [14]. Shrews generally adapt rapidly to spatial and temporal changes in prey availability [10], and the observed pattern of Common shrew abundance found in this study may, thus, be attributed to indirect effects of livestock grazing affecting the distribution of Common shrew food.
Unlike for the field voles [11], we found no qualitative differences between Common shrew individuals caught in the three grazing treatments. That is, no differences in body mass, reproductive output, or sex ratio between treatments. The only qualitative difference we found was between individuals from the two meadows studied, and individuals from the western meadow were lighter than individuals from the eastern meadow. This difference in body mass points out meadow West as being sub-optimal compared to meadow East. Generally, only few shrews were caught on this meadow, and generally the populations on meadow West fluctuated more irregularly compared to meadow East. Meadow West was generally more water-logged and flooded more often than meadow East, and may therefore be a less suitable and more unpredictable habitat than meadow East. Shrews are rapid colonisers [15], and Common shrew numbers on meadow West was therefore probably more determined by an unstable alternation between immigration and emigration, whereas the shrews on meadow East belonged to more stable populations. Recapture rates were, however, too low the verify this.
The consistent response of the insectivorous Common shrew and the rodent Field vole [11] to grazing intensity across these two, highly different meadows stresses low intensity livestock grazing as a highly suitable means in today's meadow management, at least in the short run. Long-term changes in meadow vegetation composition etc. induced by grazing livestock may either alter or consolidate the response of both rodents and insectivores to livestock grazing reported here.