A summary of MSc dissertation by Ruth Hanniffy (summer 2005)
A study was carried out to determine the density and habitat preferences of six species of small mammals at Paxton Pits. Small mammals tend towards different habitats to fulfil their dietary and nesting requirements. As a result certain species often co-exist: Apodemus sylvaticus (Wood mouse), Clethrionomys glareolus (Bank vole), Sorex araneus (Common shrew) and Sorex minutes (Pygmy shrew) inhabit broadleaved and mixed woodland in the south of England, while Microtus agrestis (Short-tailed field vole) and Micromys minutus (Harvest mouse) favour rough grassland.

Harvest mice are notoriously difficult to trap and as a result are highly under-recorded. However, distribution has most certainly reduced over the past 30 years so that populations are now confined to the south and east of England. Harvest mice are indicative of the health of fields and hedgerows and loss of this species around the countryside has been attributed to changes in agricultural practices over the last three decades.

Capture-mark-recapture using Longworth trapping was carried out over consecutive weeks on five habitat types. Vegetation at each site from week one to eight was recorded to identify the dominant species in a five-metre radius.

Densities varied greatly with habitat type, however these differences were for the most part not statistically significant. Wood mice were particularly abundant in scrub-grassland borders, highly grazed grassland and in the field margins of arable land. Bank voles, as the name implies, were most plentiful on banks of lakes and ditches, of both high and low vegetative cover. They were also abundant in swamp and marginal habitat and in the field margins of arable land. Common shrews inhabited rough grassland and marshy grassland, which presumably supports many invertebrate communities. They were also present in the meadow hedge that runs over a ditch and the swamp habitat. Pygmy shrews also inhabited the grassland-marsh of the meadow. Only two short-tailed field voles were caught in swamp habitat and recaptured in the nearby scrub-grassland.

At Paxton Pits, the number of resident and visiting raptors is extensive. Records of raptors place the majority on the north section of the Pits, away from the nature reserve where the study was carried out. Kestrels and occasionally barn owls hunt over the arable land, where the abundance of Wood mice and Bank voles is extremely high. Small mammals will only be available to most raptors on the larger arable fields. However, at least two pairs of tawny owls nest on the reserve and will hunt over woodland and scrub.

The role of management and deer and rabbit browsing on various parts of the reserve were determined and the relationships between these factors and the diversity of small mammal species in these areas was considered. Possibilities for future study on the reserve and recommendations for the efficient monitoring of harvest mice were made.