Pol. J. Ecol. - BIOL

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POLISH JOURNAL OF ECOLOGY
(Pol. J. Ecol.)
60
3
621–628
2012
Short research contribution
Leszek RYCHLIK1,*, Sara CHURCHFIELD2, Jan R.E. TAYLOR3,
Paweł KARDYNIA1 and Łukasz OŁDAKOWSKI3
1
Department of Systematic Zoology, Institute of Environmental Biology, Adam Mickiewicz University,
Umultowska 89, PL 61-614 Poznań, Poland, *e-mail: [email protected] (corresponding author)
2
Department of Anatomy & Human Sciences, Guy’s Campus, King’s College London,
GB London SE1 1UL, Great Britain
3
Institute of Biology, University of Białystok, Świerkowa 20 B, PL 15-950 Białystok, Poland
LIVE-TRAPPING SMALL MAMMALS UNDER SNOW:
A PROTOCOL FOR MAXIMISING CAPTURES
AND MINIMISING MORTALITY
ABSTRACT: Difficulties in investigating
shrews in the wild in winter, especially in trapping
them and keeping them alive during live-trapping
studies, have been the main reason for serious deficiencies in our knowledge of their ecology. We
developed a live-trapping protocol which allowed
us to maximise capture rates and minimise mortality of shrews. We used wooden box traps with a
nest-chamber, which we set in plywood ‘chimneys’
with removable roofs. Chimneys facilitated suitable positioning of traps and protected them from
being blocked by snow. This resulted in a high
trappability (up to 20.2 shrews and 8.2 voles per
1000 trap hours), a large proportion of recaptures
(most shrews were recaptured, often repeatedly)
and a very low mortality rate (<0.09 shrews and
0 rodents per 1000 trap hours) despite sub-zero
temperatures and deep snow cover. This allowed
us to pursue an intensive live-trapping study, using the CMR-method, of shrews wintering in the
Narewka river valley (north-east Poland). Because
of the high trappability and minimal mortality,
the presented protocol can be recommended to
study winter ecology and conservation biology of
such fragile and strictly protected small mammals
as shrews.
KEY WORDS: new method, trappability,
winter trapping, winter ecology, shrews, voles
journal 31 v02.indb 621
Live-trapping and capture-mark-recapture programmes are widely used in the study
of small mammals to gain information about
seasonal variation in population density, activity and movement patterns, spatial distribution and other aspects of their population dynamics. Many designs of traps are effective in
catching small mammals but all are problematic when used under winter conditions with
snow: to set traps in the subnivean environment (where small mammals are most active)
is difficult because snow-fall hides traps and
blocks their entrances or closing mechanisms.
Consequently, relatively few live-trapping
studies have been carried out in winter under
snow (see below). Many small mammals do
not hibernate and many aspects of their ecology, behaviour and bioenergetics in winter
have yet to be studied. Shrews, for example, are
amongst the smallest of mammals with a high
surface area/body mass ratio and the highest
metabolic rates and energy requirements (Vogel 1980, Tay lor 1998, O cho cińska and
Tay lor 2005). However, many interesting
questions concerning their survival in northern winters go unanswered because of the difficulties of trapping them under the snow and
keeping them alive in good condition for subsequent study and release.
2012-10-12 08:43:35
622
Leszek Rychlik et al.
Several studies have pioneered the use
of shelters to protect traps from snow. S op e r (1942) instructed how to set traps under
spruce bough cover, under blocks of frozen
snow, between two logs or inside hollow logs,
but he was interested in an increase of winter snap-trapping to collect more dead specimens for museum collections. Simple wooden shelters for traps were made by Ivers on
and Tu r ner (1969) and Jannett (1984).
Mer r itt (1995) used lengths of plastic pipe
cut longitudinally to cover the traps and
S ch mi d (1984) used inverted plastic wastebins. Others have constructed rectangular
or cylindrical ‘chimneys’ of wood or roofing felt placed vertically to exclude snow, at
the bottom of which is placed a trap (Pr u itt
1959, Mer r itt and Mer r itt 1978, Merr itt 1982, 1984, Pe n ny and Pr u itt 1984).
Keeping small mammals alive in traps for
mark-recapture studies presents particular
problems, especially for shrews (e.g. Yu nge r
et al. 1992). Trap design, provision of appro-
priate food and bedding, and trap inspection
regimes are all critical to their survival. Various types of live traps have been used in winter studies (see S chmi d 1984 for examples)
with different degrees of success.
Aspects of shrew winter ecology have
been studied in winter in southern and western Europe (e.g. C roi n Mi ch i els e n 1966,
C hu rch f i el d 1984, C ast i én and G os á lb e z 1999), but winters are relatively mild
there. We needed to study the winter survival
strategies of soricine shrews and the functional basis of Dehnel’s effect (D ehnel 1949,
Me zhzher in 1964, Pucek 1970) in northeastern Poland, i.e. in the area with winter
temperatures regularly falling below –10°C,
frozen soils and snow cover for 3 months.
This has necessitated the development of a
live-trapping protocol that maximises captures and survival, and meets ethical demands
about the treatment of these tiny mammals.
Details of our methodology with illustrative
results are provided here.
Fig 1. Structure and dimensions (in cm) of (A) chimney with removable roof and (B) nest-box trap
made of pine or spruce wood.
2012-10-12 08:43:36
Live-trapping small mammals under snow
623
Fig. 2. (A) Diagram and plan of a chimney installed with nest-box traps set inside, showing location of
the entrance in relation to the snow, litter and soil layers. (B) View of a chimney installed in deep snow
(Photo of S. von Merten).
We chose to use ‘chimneys’ to protect
traps from snow and facilitate their operation, coupled with specially modified box
traps which we have trialled very effectively
over the course of five winter live-trapping
sessions. Protective boxes or ‘chimneys’ were
made from plywood treated with waterproofing paint to prevent water-logging. Each
chimney measured 30 × 31 cm and 50 cm
high and was supplied with a removable lid
(roof) to allow inspection of the interior, but
no base. Gaps were cut into the walls at the
base of the chimney to allow access to small
mammals from the surrounding litter layer
(Fig. 1A).
The chimney walls were attached to each
other on three sides by strips of tough plastic
tape stapled at three points along each wall,
providing some flexibility during assembly
and disassembly. On the fourth side of the
chimney, the walls were attached using three
strips of ‘velcro’ stapled to the wood (Fig. 1A).
Disengagement of the velcro allowed the
chimneys to be collapsed and folded flat for
carriage and storage, and rapid assembly. Velcro proved resistant to water and retained its
adhesive capacity throughout. The cost of one
chimney was 90 zł (i.e. about 21 €).
During deployment, a plug of snow equal
to the base area of the chimney was removed
from the trapping site with a spade, exposing
the ground surface/litter layer. The assembled
chimney was placed in the resulting gap with
its base flush with the ground surface. Care
was taken that the access gaps at the base were
not blocked by snow or vegetation. Snow was
then packed lightly around the outer walls of
the chimney to restore a continuous cover
and protect small mammals moving through
the subnivean space (Fig. 2).
Inside each chimney, on the ground
surface, were placed two wooden box traps
of modified ‘dziekanówka’ type and size of
21 × 8 × 9.5 cm (Fig. 1B). These were designed
to include a small nest chamber at the far end
of the trap (and therefore called ‘nest-box
traps’), reached by small mammals through a
hole of 25 mm diameter so that bedding and
food could be supplied without interfering
with the trapping mechanism. Traps could be
opened from either end by means of a sliding metal strip. Nest chambers were provided
with polartec fleece as insulating bedding and
food in the form of fly (Calliphora sp.) pupae
and minced beef. The cost of one nest-box
trap was 40 zł (i.e. about 9.50 €).
The study area comprised a sedge-swamp
in the valley of the Narewka river, close to
Białowieża village in north-east Poland. This
region is characterised by cold winters with
January temperatures regularly falling below
–10oC (often below –20oC), with frozen soils
and snow cover for 3 months (pers. obs.). The
vegetation on the study plot was dominated
by reeds, grasses and sedges (Phragmites communis, Phalaris arundinacea, Bromus inermis,
Carex approprinquata and C. rostrata) plus a
diversity of forbs (mostly Urtica dioica, Filipendula ulmata and Angelica sylvestris). Scattered trees and bushes (Alnus glutinosa, Salix
spp. and Betula spp.) were also present. The
vegetation profile comprised mostly dense
2012-10-12 08:43:36
624
tussocks with additional ground cover of
mosses and a litter layer of dried grasses.
In 2006, 50 chimneys were placed in a
grid with intervals of 5 m (five rows of 10
trap points). Twenty chimneys contained two
wooden box traps, 20 chimneys contained
one box trap and one nest-box trap, and 10
chimneys contained one plastic pitfall (25
cm deep and 20 cm in diameter). Additionally, 20 nest-box traps were set singly (also
with intervals of 5 m) along other lines without chimneys. Here, box traps were dug into
the sides of grass/reed tussocks and protected against further snowfall by metal sheets
250 mm × 250 mm placed as flat roofs over
the top of the trap. This gave a total of 70 trap
points. All three types of traps were provided
with the above mentioned bait and bedding
(though only little amount of polartec fleece
could be placed in box traps without blocking
the closing mechanism).
In winters 2007–2009, two nest-box traps
were set in each chimney. In 2007 and 2008,
100 chimneys were placed in the same study
area in a grid with intervals of 5 m, giving a
total of 100 trap points (10 rows of 10 trap
points). Additional chimneys (17 in 2007 and
5 in 2008) were placed at 10 m intervals along
the outer edges of the trapping grid, and approximately 10 m from the main grid. The
grid and the outer lines covered an area of
70 × 70 m (4900 m2). In 2009, 60 chimneys
within the grid (i.e. 6 rows) and 5 chimneys
along an outer line were set.
In winter 2006, we compared the effectiveness of the nest-box trap prototypes with
standard box traps and plastic pitfalls. Trapping performed in winters 2007–2009 allowed us further assessment of the trappability and mortality of small mammals trapped
with nest-box traps set in chimneys.
All traps were open either 24 hr day and
night (when data on shrew circadian activity
were collected) or during evening and night
hours. In both situations, they were checked
at 2–3 hour intervals. Trapping was carried
out during January and February, and lasted
from 8 days in 2007 to 13 days in 2008. During trapping, ambient temperatures under
snow (within the leaf litter layer) were measured at midday (once per trapping session)
at five points within the study area, using
electronic temperature probes. Maximum
and minimum air temperatures were recorded daily, using maximum-minimum capillary thermometer. Depth of snow cover at the
study site was also noted.
Most trapped animals were released at
the place of capture immediately after recording data about them, but some animals
were taken to the laboratory for further experiments (Tay l or et al. 2010 and papers in
prep.). We have obtained permissions (no.
DOPog-4201-04-126/05/kl of 7 July 2005 and
no. DLOPiK-op/ogiz-4200/IV-7/1331/08/aj
of 15 February 2008) from the Minister of
Environment for our capturing and temporal keeping of the protected shrews, as well
as acceptances from the Local Ethical Commissions for Experiments with Animals in
Białystok (no. 2005/46 of 21 December 2005)
and Poznań (no. 10/2007 of 22 January 2007)
for our experimental methods.
There was a thick (up to 30–42 cm) covering of snow in winters 2006–2007 and below-zero ambient temperatures (minimum
–4.9 and –9.0oC, respectively), even on the
ground surface beneath the snow (about
–1.0oC) during the sampling sessions. Temperatures in winters 2008–2009 were higher
(minimum 0.7 and –0.7oC) but, with lacking
or little snow cover (see C hu rchf i el d et al.
2012), small mammals could also suffer from
heat loss. Five species of small mammals were
captured, including three species of shrews.
Common shrews Sorex araneus were captured more frequently than any other species
and bank voles Myodes glareolus were more
numerous than root voles Microtus oeconomus (Table 1).
In 2006, the rate of capture (standardised
for number of traps and hours of trapping
as trappability per 1000 trap hours) tended
to be higher when nest-box traps were used
and traps were set in chimneys. For example,
trappability of S. araneus was six times higher in nest-box traps set in chimneys than in
nest-box traps set without chimneys (Table
1). These trappabilities came from captures
of 16 and 4 individuals of S. araneus, respectively (chi-square-test: χ2 = 7.20, df = 1,
P = 0.007; the difference for individuals and
not the total number of captures was tested to
prevent pseudoreplication; no individual was
caught in both types of traps). Interestingly,
pitfalls, that are known to be very effective in
2012-10-12 08:43:36
625
Table 1. Numbers of captures and dead captures as well as trappability and mortality of small mammals
captured during four winters using three types of live-traps set in chimneys and without chimneys.
Parameter or
Winter
species
Traps set in chimneys
Trap type
Number of traps
Number of trap hours
2006
no
2008
2009
Total for
nest-box
traps set
in chimneys
yes
yes
yes
yes
yes
pitfall
box
nestbox
nest-box
nest-box
nest-box
20
10
60
20
234
210
130
594
1830
915
5490
1830
15 600
20 580
10 660
48 670
nestbox
yes
2007
Number of captures (dead captures in brackets):
Sorex araneus
6
0
74 (3)
37
52 (1)
179 (2)
18
286 (3)
Sorex minutus
2
0
3
1
5
26 (1)
5
37 (1)
Neomys fodiens
1
0
13
3
0
0
0
3
Myodes glareolus
11
0
30
15
0
23
51
89
Microtus oeconomus
0
0
0
0
3
93
2
98
1.7
5.9 (0.06)
Trappability (mortality in brackets) per 1000 trap hours:
13.5
20.2
Sorex araneus
3.3
0
(0.55)
Sorex minutus
1.1
0
0.5
0.5
1.3 (0.05)
0.5
0.8 (0.02)
0
0
0
0.1
8.2
0
1.1
4.8
1.8
0
0.2
4.5
0.2
2.0
0.5
0
2.4
1.6
Myodes glareolus
6.0
0
5.5
0
0
0
capturing shrews in summer, appeared to be
completely ineffective in winter.
Survival rates of all small mammals captured in nest-box traps set in chimneys were
very high. For the whole period 2006–2009,
the only casualties were three S. araneus and
one S. minutus, despite the large numbers of
trapping hours (48 670) and captures of small
mammals (513 in total). For comparison, only
5490 trap hours of trapping with box traps
without nest chamber resulted also in three
dead S. araneus (Table 1). Thus, the mortality of this species for capturing in nest-box
traps was 6–9 times lower than for capturing
in box traps without nest. Recapture rate for
both box trap types set in chimneys was high.
In particular, most shrews were recaptured,
and some of them repeatedly (even 20 times).
The design of our trapping chimneys
made them easy to operate and resulted in
high capture rate of small mammals, particularly shrews. The flat-pack style of design and easy assembly allowed them to be
installed rapidly. In order to avoid damage
from human, wild boar or beavers (all oc-
0.3
Neomys fodiens
Microtus oeconomus
3.3 (0.06) 8.7 (0.09)
casionally entering our study plot) we chose
not to install them before the snows came
(as had Pr u itt 1959), but instead to install
them when and where needed. This practice
also preserved them for future use (since they
were constructed only of plywood).
The dimensions of the chimneys were
such that it was possible to see if traps had
been sprung without handling them and, if
sprung, traps were within arm’s reach. Other designs of chimneys have been taller and
required additional aids to reach the traps,
on account of greater snow depths (Pr uitt
1959, Mer r itt and Mer r itt 1978). While
snow did occasionally cover our chimneys,
frequent trap inspections allowed us to brush
excess snow from the lids so that they could
be found easily. Freezing of the trap mechanism is a frequent problem in winter, especially when traps are exposed to snow and
wet. This was rarely a problem in the protective environment of the chimneys.
Wooden box traps are preferable to metal
traps for minimising mortality of captures,
and survival was enhanced by provision of
2012-10-12 08:43:36
626
insulating bedding and food for the shrews.
Despite this precaution, frequent trap checking is needed to further reduce mortality,
especially when ambient temperatures plummet. In our study, trap visits were made every
2–3 hours. The result was a total mortality of
only 1.7% of all shrew captures and 0% of rodents. Shrews may have survived for longer
in traps but we were seeking information on
24-hour activity patterns of shrews, requiring
frequent and regular checks.
To conclude, our protocol of winter
trapping chimneys and traps provided with
nest-boxes for bedding and food resulted in
many captures of small mammals, especially
shrews, with minimal mortality rate. This allowed us to pursue an intensive live-trapping
programme, using the CMR-method, for the
collection of new information about foraging habits, changes in body mass, population
dynamics, space use, and circadian activity
of shrews wintering in north-eastern Poland
(Tay lor et al. 2010, Rych li k et al. 2011,
C hu rch f ie l d et al. 2012). Therefore, we recommend the present protocol to study winter ecology and conservation biology of such
fragile small mammals as shrews, which are
strictly protected in Poland and many other
countries.
AKNOWLEGEMENTS: We are very grateful to J. Chilecki (the producer of chimneys and
traps; [email protected]), A. Arasim, B. Lewończuk
(technicians), I. Both, W. Hütz, P. Kreitschmann,
D. Matuszak, S. von Merten, E. van Nes, R. M. Ricardo Nunes, A. M. Guimaraes Nuno, J. Tapisso,
and C. van den Tempel (students of different universities) for field and technical assistance. This
study was supported by the grant no. N304 094
31/3385 of the Polish Ministry of Science & Higher Education and the budget of the Mammal Research Institute of the Polish Academy of Sciences
in Białowieża.
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Received after revision April 2012
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