Methods

1
Seasonal use of vertical hedgerow habitat by
small mammals. Dont forget the third
dimension! Dr Jenny Sneddon, School of Biological
Earth Sciences, Liverpool John Moores
university. J.C.Sneddon_at_ljmu.ac.uk
Methods This study was designed to investigate
seasonal arboreal use of habitat space by small
mammals in two 210 m sections of
hawthorn-dominated hedgerow (Crataegus monogyna
Plate 1) on Cheshire farmland. Sixty-three
Longworth traps were set 10 metres apart in
vertical lines of three covering the uncut body
of each hedgerow (Plate 2). Traps positions were
2312 cm 27 13 cm, 7612 9216 cm 15315
16717 cm above the ground for hedgerows A B
at lower, mid and upper levels respectively.
Trapping occurred post 1 week of pre-baiting for
a fortnight in each hedgerow at each season. Trap
spacing and trapping protocol were adapted from
TEW et al. 1994b. Trapped animals were
individually weighed, marked with indelible pen,
and sexed to assess use of lower, middle and
upper levels of each hedgerow. Trapping occurred
under license approved by Scottish Natural
Heritage.
Why do the study? Wood mice (Apodemus) and bank
voles (Clethrionomys) are well adapted to
hedgerow habitats, and have been long established
as good climbers (FLOWERDEW 1993 2004
TATTERSALL et al. 2002). Hedgerows abutting
fields are relatively confined and linear habitat
affording enhanced protection for small mammals
in contrast to open spaces. They are known to
provide an important food resource for small
mammals in the fruiting season (TEW 1994 OUIN et
al. 2000). Ecological studies of small mammals
commonly use ground level trapping grids that are
two-dimensional and take no account of the third
dimension i.e. climbing ability. I therefore
decided to confine traps to the vertical
dimension of hedgerows to emulate their
attractiveness as a purely arboreal habitat
resource over an annual cycle. There is one
study on vertical use of hedgerow habitat space
in the UK by small mammals (POLLARD and RELTON
1970) when 12 unsecured traps were placed above
ground in a hedgerow. Trapping sessions were
sparse lasting only 4 days with no pre-baiting or
marking of animals.
Plate 1. Crataegus monogyna dominated hedgerow
Plate 2. Vertical positioning of Longworth traps
Main findings (refer to Figs 1 2). Ambient
temperatures were 162.9 oC in late summer 2003,
63.3 oC in mid winter 154.8 oC in early
summer 2004. Sex ratio in trapped animals not
biased for wood mice (?2 2.40 Plt0.1209) or voles
(?2 0.86 Plt0.3540) df1. None of the individuals
caught in hedge A were caught in hedge B.
Overall trap occupancy was 15 20 of all traps
laid (Hedgerow A) and 6-11 (Hedgerow B facing
prevailing wind). Trap occupancy was
significantly different between lower, mid and
upper levels (Friedmans test for Repeated
Measures) for both hedgerows, for both species,
with Apodemus dominating the catch by 1.5 3
times plt0.0001). Middle levels had significantly
higher numbers of wood mice in mid winter in
hedgerow A (Plt0.001 GLM Repeated Measures test).
There was an inverse relationship between
numbers trapped and height of trap for voles
(r-0.741 plt0.022 hedgerow A r-0.700 plt0.036
hedgerow B) but not wood mice (r-0.26 plt0.494
hedgerow A r-0.234 plt0.544 hedgerow B). Over
90 of all marked animals released returned to
the same trap the remainder to one in the same
vertical line. Populations were estimated by
minimum number alive to overcome trap bias across
all seasons. Data (total trapped total marked
for trapping effort) ranged from 7-39 voles and
19-85 wood mice per trapped 210 m of hedgerow.
Recaptures ( total individuals trapped) were
11, 21 7 for wood mice 12, 9 11 for
voles in late summer, mid winter and early summer
respectively.
Fig 1. Woodmouse capture data (including
recaptures at lower, mid and top levels of
hedgerow over the span of the study.
Fig 2. Vole capture data (including recaptures)
at lower, mid and top levels of hedgerow over the
time span of the study.
C. glareolus
Conclusions. This study showed that the
vertical dimension of hedgerows contains
significant numbers of small mammals in
proportion to those found in open arable habitat
(TEW et al. 1994b), particularly wood mice,
during all seasons of the year. Arboreal hedgerow
habitat should thus be included in trapping grids
in population studies. Recaptures suggested
that small mammals use well defined
three-dimensional habitat spaces within hedgerows
of less than 10m in length and averaging the
uncut body of the hedgerow in volume. Recapture
data did not plateau over the fortnight of
trapping activity suggesting that hedgerows are
not closed habitats but are a component of a well
defined three dimensional component within a
wider habitat mosaic. References FLOWERDEW, J.
(1993) Mice Voles Whittet Books. UK. Pp17-60
FLOWERDEW, J. SHORE, R.F. POULTON, S.M.C.
SPARKS, T.H. (2004) Live trapping to monitor
small mammals in Britain. Mammal Review 34,
31-50. POLLARD E. RELTON, J. (1970) Hedges V. A
study of mammals in hedges and cultivated fields.
J Appl Ecol 7, 549-557. OUIN, A. PAILLAT, G.
BUTET, A. BUREL, F. (2000) Spatial dynamics of
wood mouse (Apodemus sylvaticus) in an
agricultural landscape under intensive use in
Mont Saint Michel Bay (France). Agr Ecosyst
Environ 78, 159-165. TEW, T.E. (1994) Farmland
hedgerows habitat corridors or irrelevant? A
small mammals perspective. Hedgerow management
and nature conservation. (eds TA Watt and GP
Buckley) Pp80-94. TEW,T.E. TODD, I.A.
MACDONALD D.W. (1994b) The effects of trap
spacing on population estimation of small
mammals. J. Zool. Lond.233, 340-344. TATTERSALL,
F.H. MaCDONALD, D.W. HART, B.J. JOHNSON, P.
MANLEY, W. FEBER R. (2002) Is habitat linearity
important for small mammal communities on
farmland? J. Appl. Ecol 39,643-652.