Investigation into the use of field edges by small mammals on the Writtle College Estate
traps were staggered, with the outer trap a few centimetres inside the junction with the cultivated
area of the field, the next in the middle of the uncultivated strip and the inner trap a few centimetres
inside the field boundary, with this sequence repeated along the section. This allowed a comparison
to be made between the mammals' utilisation of the edge adjacent to the cultivated area of the field,
the middle and the boundary edge of the uncultivated strips.
Trapping was carried out over four periods; in the autumn of 2001, the spring and autumn of 2002
and the spring of 2003. Animals were trapped using Longworth traps filled with straw and baited
with oats and blow-fly pupae (Gurnell & Flowerdew 1994). The traps were checked on eight
consecutive mornings and evenings in each period and the trapped animals were identified and
released at the point of capture. The species and location of each trapped mammal was recorded.
Results
During this study a total of 1203 individuals were captured, made up of seven species of small mammal.
Wood Mouse Apodemus sylvaticus, Bank Vole Clethrionomys glareolus and Common Shrew Sorex
araneus were the most abundant, with 526, 428 and 216 individuals respectively. These comprised
97% of the mammals captured. The other species, namely House Mouse Mus musculus, Field Vole
Microtus agrestis, Pygmy Shrew Sorex minutus and Harvest Mouse Micromys minutus were captured
in too few numbers for meaningful analysis. However, it was noted that all of the House Mouse, Field
Vole and Harvest Mouse were captured in the autumn, all of the Pygmy Shrew were captured in the
spring, and all of the Field Vole and Harvest Mouse were captured in the uncultivated margins.
Of the combined total numbers of Wood Mouse, Bank Vole and Common Shrew; there was no substantial
difference between the sections with uncultivated margins and those without margins. However, the
total numbers of Wood Mouse (Figure 1) varied substantially between the different margin types with
the largest number' found in the sections without margins. Bank Vole numbers also differed substantially
but this species was more abundant in the uncultivated margins. Common Shrew was also more
abundant in the uncultivated margins but the difference in numbers was not as great.
In both autumn and spring (Figure 2), more Wood Mouse were captured in the sections without
uncultivated margins than those with uncultivated margins. Conversely, in both autumn and spring
more Bank Vole were captured in the uncultivated margins, as were Common Shrew. In the case of
Bank Vole in the spring there were more than three times as many captured in the uncultivated
margins than in the sections without uncultivated margins.
In the autumn (Figure 3) the numbers from the three locations within the uncultivated margins did
not differ substantially for Wood Mouse or Common Shrew. There was, however, a substantial
difference for Bank Vole. Further examination of the autumn data determined that, of the 117 Bank
Vole captured within the uncultivated margins, there were 63 from the inner location, 43 from the
middle location and just 11 from the outer traps at the junction of the margin and the crop.
There was no substantial difference between the locations in the spring for Wood Mouse, Bank
Vole or Common Shrew.
Discussion
It was observed during this study that the uncultivated strips selected as trapping sites were along
field edges that abutted mainly grassy areas whereas the field edges without uncultivated margins
were mainly along established hedgerows with few grassy places. This meant that the uncultivated
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Essex Naturalist (New Series) 21 (2004)