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Technical manual for sampling small mammals in the Arctic

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Version 1



-


A collaborative document made with the financial aid from Polar Knowledge Canada
About the authors
-, M.Sc., is a research assistant at Université Laval, Québec (QC), and
has been working extensively on the ecology of the Arctic for 15 years.
, M.Sc., is a Ph.D. student at Université Laval, Québec (QC), and has been
studying the ecology of small mammals in both boreal and arctic ecosystems.
 , Ph.D., is a professor at Université Laval, Québec (QC), and has been
conducting ecological research in the Arctic for more than 25 years. He is the leader of the
Ecological Studies and Environmental Monitoring Program at Bylot Island, Sirmilik National
Park, NU.
The first version of this manual has been written and published in 2015.
It was printed at Université Laval, Québec (QC), Canada.
© All copyrights are retained by the authors. This manual was intended to be publicly available.
Applying the techniques described in this manual cannot guarantee the welfare of
captured animals under all circumstances and thus they should not be be used by untrained
persons. Obtaining a federal and/or provincial/territorial permit is mandatory to conduct field
research in northern Canada. Approval by an institutional animal welfare committee is also
required in most situations before trapping animals for research purposes.
Citation: -. Technical manual for sampling
small mammals in the Arctic ‒ Version 1. Centre d’études nordiques, Université Laval, Quebec,
55 pages.



1. INTRODUCTION ................................................................................................................... 1
2. Basic sampling notions ...................................................................................................... 3
2.1. Transect ....................................................................................................................... 3
2.1.1. General definition ............................................................................................. 3
2.1.2. Setting up a transect ......................................................................................... 4
2.1.3. Surveying a line transect .................................................................................. 4
2.2. Plots or grids ............................................................................................................... 6
2.2.1. General definition ............................................................................................. 6
2.2.2. Setting up and surveying plots or grids ............................................................ 6
2.3. The use of field books and datasheets ........................................................................ 7
3. Winter tracks left in the snow pack.................................................................................... 9
3.1. Description of the method .......................................................................................... 9
3.2. Time period ............................................................................................................... 10
3.3. Material required ...................................................................................................... 10
4. Burrows and runways ...................................................................................................... 11
4.1. Description of the method ........................................................................................ 11
4.1.1. Burrows .......................................................................................................... 11
4.1.2. Runways ......................................................................................................... 11
4.2. Time period ............................................................................................................... 12
4.3. Material required ...................................................................................................... 13
4.4. Examples of runways ................................................................................................ 14
5. Faecal deposits ................................................................................................................. 15
5.1. Description of the method ........................................................................................ 15
5.2. Time period ............................................................................................................... 16
5.3. Material required ...................................................................................................... 16
6. Winter nests ..................................................................................................................... 17
6.1. Description of the method ........................................................................................ 17
6.1.1. Opportunistic nests ......................................................................................... 19
6.2. Time period ............................................................................................................... 19
6.3. Material required ...................................................................................................... 19
6.4. Determination of species, reproductive activity and predation ................................ 19
6.4.1. Faecal material in/around winter nests ........................................................... 19
6.4.2. Bones and carcasses ....................................................................................... 20
6.4.3. Hairs ............................................................................................................... 21
7. Snap trapping ................................................................................................................... 23
7.1. Description of the types of traps ............................................................................... 23
7.2. Description of the method ........................................................................................ 23


7.3. Time period ............................................................................................................... 26
7.4. Material required ...................................................................................................... 26
8. Live trapping .................................................................................................................... 29
8.1. Description of the types of traps ............................................................................... 29
8.1.1. Live traps ........................................................................................................ 29
8.1.2. Pitfall traps ..................................................................................................... 30
8.2. Description of the marking techniques ..................................................................... 31
8.2.1. Ear-tags ........................................................................................................... 31
8.2.2. PIT tags (Passive Integrated Tranponder) ...................................................... 31
8.2.3. Pros and cons of each marking method .......................................................... 32
8.3. Description of the method ........................................................................................ 32
8.3.1. Field procedures for Longworth®/Sherman® traps ...................................... 33
8.3.2. Field procedure for pitfall traps ...................................................................... 36
8.4. Time period ............................................................................................................... 37
8.5. Material required ...................................................................................................... 37
9. Photo trapping .................................................................................................................. 39
9.1. Description of the cameras ....................................................................................... 39
9.2. Description of the method ........................................................................................ 39
9.2.1. Summer deployment of cameras .................................................................... 40
9.2.2. Winter deployment of cameras ...................................................................... 41
9.3. Material required ...................................................................................................... 42
10. Identifying small mammal species and their characteristics ............................................ 45
10.1. Species ................................................................................................................... 45
10.1.1. Dentition ...................................................................................................... 47
10.2. Sex ......................................................................................................................... 47
10.3. Reproductive conditions ........................................................................................ 48
10.3.1. Females ........................................................................................................ 49
10.3.2. Males ............................................................................................................ 50
10.3.3. Non-reproductive female VS non-reproductive male .................................. 50
10.4. Age group .............................................................................................................. 51
10.4.1. Body weight ................................................................................................. 51
10.4.2. Age and reproductive condition ................................................................... 52
11. Bibliography .................................................................................................................... 53
12. Appendix .......................................................................................................................... 55
1
I
t is impossible to know the exact number of
individuals of an animal or plant species
occupying a given territory. This is why, over
the years, biologists have developed various
techniques to estimate their abundance, for
instance by counting a subset of the
population of interest or sampling portions of
it. Estimating the abundance and studying the
demography1 of wildlife populations are key
attributes to assess the biodiversity and make
sound decisions about conservation. Wildlife
management starts with a better understanding
of how wildlife populations change over the
years (Figure 1.1) and why: is the population
declining or is it growing? Is the population
abundance abnormally low? What
environmental or human-related factors are
associated with those changes?
are an important component of many
ecosystems and especially in the tundra
because they are the main prey of several
mammalian predators and birds of prey.
They are also important for some plants as
they help disperse their seeds. In forests,
some small mammals have been shown to
help control insect pests by eating larva
and caterpillars while others can cause
damage to plantations. Within cities and
agricultural lands, they are often seen as
pests because they carry diseases and they
can damage crops. Their ecological
importance has encouraged the
development of many tools to study their
populations (Krebs et al. 2008).
In the Arctic, several methods have been
proposed to study lemming and vole
populations. In this document, we review 7
sampling techniques that can be used to
estimate the relative or absolute abundance of
small mammals and provide information on
population characteristics, such as species
composition, age group, sex, reproductive
condition and body weight. Each method has
its own advantages and disadvantages and we
thus highlight in the text the pros and cons of
each of them. As you will discover in this
manual, the methods that can be used in the
field often depend on limitations imposed by
financial or time constraints. Small mammals


© Dominique Fauteux
© Dominique Fauteux
1The study of the growth and decline of an animal population and of the factors (reproduction, mortality) affecting
this population (Krebs 2009).

A population fluctuating regularly


3
C
ounting and measuring all individuals in an animal population is usually impossible, either
because there are too many individuals, they move or they live under cover and are
therefore difficult to see or catch. To circumvent this problem, we usually divide the
populations in a number of smaller units called samples. These samples can be monitored with
small plots or geographical lines (e.g. transect, see below) where we try to determine how many
individuals are present (see Figure 2.1). Once the number of individuals has been determined
for this small area, extrapolation can then be done to the whole area occupied by the population
of interest. This process is called sampling, and the way these samples are spatially structured, a
sampling design.
2.1. TRANSECT
2.1.1. General definition
A transect is a line geographically positioned and used in the field to carry out sampling.
One person typically walks along the transect previously delimited on a map. This method is
useful to find animals or objects that move little or can be located before they move. With the
use of a Global Positioning System (GPS) receiver in the field, an oberver can walk along a pre-
defined line while keeping an eye for the elements of interest. All observations of the elements
of interest should be recorded (e.g. winter tracks, nests, burrows, runways or faecal deposits).
Transects can also be used to set up trap lines (see Section 6 on snap trapping). A particular
case of transect is what we call the line transect sampling. This sampling method requires the
recording of very specific information, as explained below. It is thus important to distinguish
the terms transect line (a general term to refer to any transect) from the line transect method.
Example of samples geographically located in the landscape.

4

1. Select a homogenous patch of habitat suitable for small mammals based on information
available in the literature and by studying maps or by going directly in the field to examine
the area and make sure that the selected patch does not include unsuitable areas. A transect
crossing a lake is not very useful!
2. Typically, transects will follow straight lines defined by two geographical locations: the
beginning and the end of the transect. GPS receivers can be used to draw a line between
these two points (i.e. a route) so that the observer can walk along that line.
3. When the beginning of the transect is reached in the field, it is useful to use the “track”
function so your GPS receiver can save your path for future reference.

This particular form of transect was developed to account for the fact that as we walk
along a transect, elements may not only be seen on the transect itself but also on either side of
it, up to a certain distance. However, all these elements may not always be visible due to the
uneven topography and the long distance separating the observer from some elements (Figure
2.2). The basic principle of this method is that we assume that all elements present on the line
itself will be seen but the chance of detecting an element decreases the farther it is on either
side of the transect.
Schematic view of a line transect sampling. The thick line represents the transect. The solid
dots are elements detected by the observer when walking along the transect while open dots were not
detected either because of the uneven topography or their distance from the transect. The dashed line
represents the perpendicular distance from each element to the transect line.

5
Here is how is sampled:
1. Walk slowly along the transect and make sure that you do not move away from it (look at
your GPS). If you walk away from the transect, move back on the transect as soon as
possible.
2. Depending on what is being surveyed, a GPS location of each element encountered (e.g. a
nest, a burrow, etc.) is usually recorded.
3. Many (often the majority) of elements encountered will be located on the transect itself or
fairly close to it (Figure 2.2). However, some will be seen away from it and you will need
to record the perpendicular distance between each element encountered and the transect
itself. This distance can be recorded directly in the field or later using a mapping software,
if you have recorded the location of each element with your GPS receiver. This last
measurement is used to estimate how far the objects can be seen and determine the area
covered by the transect (i.e. length of the transect × maximum width).
4. Note that the type of habitat you are surveying, its topography (e.g. hummocks) or the
environment (e.g. tall grass, willow bush) will affect your ability to detect all the elements
of interest. As mentioned above, you have less chances of detecting an element that is far
away from the transect than close to it. This is normal and is taken into account by this
method. However, if you find a new element while moving away from the transect (e.g. to
record the GPS coordinate of a newly detected element), you must not record that
additional element because it was not detected while you were travelling on the transect
path.
5. Record all the information collected in your field book. This information includes the exact
coordinates (from your GPS receiver) of each element detected and the perpendicular
distance from that element to the transect line (see Figure 2.2).
FAQ: HOW LONG SHOULD A TRANSECT BE?




            


          
             
             
   
 


6


Plots (often referred to as ‘quadrats’) are areas of pre-defined shape and size where all
elements of interest encountered are counted. Grids can be considered as a large plot divided
into several stations following a Cartesian plane (i.e. lines intersecting each other
perpendicularly). This method is extensively used for plant sampling but is also suitable for
animals or objects that do not move a lot or can be captured by traps or fixed cameras.
A square or rectangle is the most popular shape used in grid or plot surveys because they
are easier to set up in the field and their boundaries are easily defined. The shape chosen should
be adapted to the habitat selected for the survey. For example, if the habitat patch is long and
narrow, then a rectangular shape may be more appropriate than a square one.

Select a homogenous patch of habitat that is suitable for small mammals based on
information available through the literature, by studying maps or by going directly in the field
to examine the area.
1. Two methods can be used to locate the stations of a grid. The first method requires the use
of a GPS receiver. Mark the first corner of the grid with a visible wooden stake at least 60
cm high, painted orange or marked with flag tape rolled around the stake. Avoid fixing the
tape as a floating flag because strong wind and sunlight will degrade it rapidly and pieces
of tape will be found all over the place. Then determine the distance and direction of the
next station (20 or 30 m east/west/north/south from the current position). Walk with a GPS
receiver to this new destination, record the position in your unit and mark the new station
in the field. Do this until all stations have been positioned. The second method requires that
all the stations have been pre-determined in a mapping software on a computer and their
position entered in a GPS receiver. Once on site, the observer simply has to walk to each of
those positions with its GPS receiver and mark each of them in the field.
2. The lines of a grid should be equally spaced out from one another, with lines running
parallel to each other in one direction (e.g. left to right, rows) identified by a different
number, and those running in the other direction (e.g. top to bottom, columns) by a
different letter. For sampling tundra small mammals, each line should be typically spaced
out by 20 to 30 m. Each station should be marked in the field with a small stake (e.g. a
bamboo stick), labelled with the column and row ID (e.g. C05; see Figure 2.3).
3. To conduct a complete search of a large plot/grid, two or more observers should walk
parallel lines approximately 5 m apart (or closer in more rugged terrain). When surveying a
large grid in this manner, stations marked with stakes (as previously described) are very
useful to stay on track because they can be used as landmarks or guides. When surveying a
plot, make sure to keep your heading using a GPS receiver.

7
4. Depending on what is being surveyed, GPS coordinates of each element (e.g. a nest, a
burrow, etc.) sampled within the grid/plot should be recorded.
5. Record all the information collected in your field book.

Field books are probably man’s best friends when gathering data in the field. Regardless
of the equipment needed to conduct field work, carrying a field book to write down data is an
essential component and is often easier to use than carrying a clipboard with datasheets. The
weather can also be unpredictable and losing a datasheet to the wind can mean losing a lot of
precious information and time! However, depending on the survey being conducted, the amount
FAQ: WHAT PLOT/GRID SIZE SHOULD BE USED?
     





               

            
           

(left) Example of a 180×180 m grid with 100 stations at 20-m intervals. Letters are
used to label the columns and lines are labelled using numbers; (right) example of a 180×180 m
plot with the corner stakes numbered from 1 to 4.

8
of data that needs to be recorded in the
field can sometimes be difficult to
remember, especially if the list is long.
Hence, it is a good idea to printout a
small version of the datasheet with the
codes that you may need to use and to
keep it in your field book for reference
when in the field. This way, you won’t
forget important details.
When sampling for small
mammals, as with any other ecological
surveys, notes recorded in field books
should be transferred to hard copy
datasheets as soon as possible when you
get back to your base of operations. This will allow you to see if all the required information
was correctly recorded in the field. These datasheet should also be entered in a computer
spreadsheet software (e.g. Excel) or using specialised data entry forms (e.g. in Access) when
returning from the field for long-term data storage. Recently, electronic tablets protected with
rain-proof casings have been used directly in the field for rapid data entry but the cost of this
method has to be considered.
© www.dendrotik.com

© Dominique Fau-


9

Lemmings remain active under the snow
throughout the winter and move while searching
for food and building their nest for protection.
When digging tunnels at the base of the snow
pack, lemmings leave tracks that may be seen
during snowmelt. However, certain weather and
snow conditions may be necessary to create
easily visible tracks at snow melt (see pictures).
The principle behind this method is that the
more lemmings there are, the more tracks will
be found at snow-melt.
Winter tracks may be best counted while
walking along a transect (see Section 2.1.).
Count all tracks seen from the transect but
do not move away from it.
We recommend using 500-m long transects
running through a homogenous patch of
habitat. Transects conducted in snow drift
areas (e.g. along the embankment of a
stream, parallel to the stream) are more
likely to encounter small mammal tracks at
snow melt. We recommend conducting
several transects (10 or more) to have a
good spatial coverage of the area. If
resources are limited, you may reduce the
length of each transect rather than the total
number. While walking along the transect,
all individual tracks should be counted. An
individual track is one that does not connect
with another track while branches are tracks
that meet another one at a junction point
(see Figure 3.1). Branching tracks can also
be counted but separately: for example, you
could count 31 individual tracks along a
given transect and 132 branches.
© Denis Sarrazin


-

10

The survey should be conducted near the
end of snow melt, when the base of the snow
pack starts to be exposed. This should be in May
or June, depending on the area. The time to
conduct winter track surveys is very limited,
though spatially variable: in snow drift areas,
winter track surveys will occur later than in other
areas due to the delayed snow melt at those sites.
The time window to conduct such survey within
a given habitat is likely to be only a few days,
depending on the speed of snow-melt.

Field book and pencil
GPS receiver
Measuring tape
Wooden stakes (optional)
In this situation, there are 3 separate
winter tracks. The first track has no branch, the
second track has 2 branches, and the third track
has one.
Pros
Cheap and fast
Not necessary to kill or capture
animals
Cons
Imprecise abundance estimates
(sometimes unclear if tracks are
individual or a branch of another track)
Dependent upon snow conditions
Tracks visible only during a short
period at snowmelt

11


Several species of small mammals that live in dry habitats such as the collared lemming
can dig burrows in the ground to hide from predators during the summer. The relative
abundance of these species can then be estimated by counting the number of active burrows in a
specified area. The method, however, can be difficult to apply in areas where boulders are
abundant because these provide natural hideaway for lemmings, which eliminates the need to
excavate burrows.
Sampling small mammal burrows can be done using either a plot (systematic survey) or a
simple transect line (see description of each sampling design in Section 2). As for other
sampling methods, you should aim to count burrows on several plots or transects randomly
scattered across your study area. A minimum of 50 plots (400 m²) or 10 transects of 500 m long
may be necessary to obtain good estimates of abundance. Transects should be permanent and re
-sampled every year.
Examine each burrow that you encounter while walking along your transect (or while surveying
your plot) and classify them as active, inactive* or unknown. Count all burrows whether active
or inactive.

Some species will consistently use the same paths to move around, often using natural
features of the environment such as frost cracks or along a large rock. Repeated use of these
paths will cause trampling of the vegetation, often accompanied by other signs such as grazing
marks or faeces, and will result in runways that are clearly seen as mini superhighways through
the vegetation. Surveying for small mammal runways should be conducted in habitats suitable
* TIPS! ‒ Active burrows
Active burrows     fresh digging  soil thrown out  
 fresh 
faecal pellets
Inactive or
old burrows      spider webs 
             
   


12
for the formation of runways, which are typically those
with an extensive moss or herbaceous plant cover, such
as in wet sedge meadows. The use of transects is
probably the most suitable method for counting runways.
As for burrows, you should aim at sampling several
transects randomly scattered across your study area.
Transects can be done in exactly the same place
year after year if they are permanently marked with
stakes. Searching for runways can be tedious in some
habitats because you may have to crawl on the ground
while searching for covered runways such as those in
frost cracks). The method proceeds as follows:
1. Lay out a measuring tape or a rope in a straight line
across an area of suitable habitat. If possible, use
permanent stakes to locate these lines.
2. Moving along the line, record for each 15-m
segment the number of active runways* cut by the
line. Some runways will snake back and forth across
the transect line and will be counted several times.
3. Count enough 15-m segments to obtain a total of
500 m. When small mammal numbers are low, you
may find few active runways.

Burrow and runway counts are best done in July or August.
© Dominique Fauteux


 
© Dominique Fau-
© Dominique Fauteux

13

50-m to 100-m measuring tape
Field book and pencil
GPS receiver
Wooden stakes
Pros
Cheap and easy to do
Not necessary to kill or capture
animals
Cons
Limited to species that dig burrows or
use runways
Presence of burrows/runways
depends on the type of soil
Require experience to make the
distinction between active/inactive
burrows
Tedious work, could take a few hours
to a whole day to survey an entire
habitat
Difficult to implement in areas with
lots of boulders or some vegetation
types (e.g. tussock tundra) because
individuals will hide under rocks or
large dead litter accumulation and will
not dig burrows
* TIPS! ‒ Active runways


     
fresh faecal pelletsfresh clippings
 within a few meter
active
               



14
4.4. EXAMPLES OF RUNWAYS
© PolarTREC (www.polartrec.com)

© Frank Kelley (www.polartrec.com)
© Jaap Mulder
© Dominique Fauteux




15

Sampling faecal deposits is one of the oldest and most classic methods to assess the
relative abundance of wildlife populations, probably because of its simplicity and suitability for
most ecosystems. Faecal deposits are typically monitored using transects. For species that
produce well defined faecal masses, such as large or carnivorous mammals, the line transect
method described in Section 2.1 can be used. However, this formal sampling method cannot be
used with small rodents due to the small size of their faecal pellets and because faeces are often
spread over relatively large areas. A more subjective approach must thus be used. An observer
should walk along the transect and record all faecal deposits encountered on it. All faecal
deposits that do not cross the transect are ignored. The same recommendations made for
burrows/runways regarding the length and number of transects apply here. As with the previous
methods, transects should be run in sites with suitable habitat for small mammals.
When a faecal deposit is encountered on the transect, the following information should be
recorded:
What species? More information on how to determine the species from faeces may be
found in Section 10.
How large is the faecal deposit? The size of the deposits could be classified according to a
semi-quantitative scale: 1-10, 11-100, 101-1000, or >1001 pellets. The size of the deposits
will depend on how long one individual used the local area and how many individuals used
it.
Is the faecal deposit recent (current year) or old (one year old or more)? The relative age of
faecal deposits can be determined by the state of degradation of the faeces. Characteristics
of old faeces are generally as follows: pale colour, dry, partly imbedded in the soil, and
covered by dead vegetation. Recent faecal deposits are generally dark green or dark brown/
reddish, sometimes damp but often dry, and clearly on top of the soil or vegetation.


© Dominique Fauteux

16

Surveying for faecal deposits should be done during early to mid-July when there is no
more snow and all deposits have been exposed. Ideally, surveys should be done under dry
conditions because old faeces can become wet when it rains, which will make more difficult the
evaluation of the freshness of the deposits.

Field book and pencil
50-m to 100-m measuring tape
GPS receiver
Wooden stakes
Pros
Quick, cheap, and easy to do
Provide a reliable index of
presence/absence of a species
in an area
Not necessary to kill or capture
animals
Cons
Give imprecise estimates of
abundance
Difficult to determine when the
faecal deposits were made (current
vs. previous year)
Determining species is not always
easy
Faecal deposits subject to washing
by heavy rain

17

Lemmings and some vole species build nests mostly made of dead herbaceous vegetation
to keep warm and reproduce during the winter but they abandon them when spring comes.
Once snowmelt is over, the nests appear on the tundra as small balls of dead vegetation (~10-15
cm in diameter). We can obtain an index of the winter abundance of small mammals by
counting these nests after snow-melt. There are 2 possible approaches to sample winter nests:
line transects and plots/grids.
If you know the species of small mammals present in your study area, you can
concentrate your search effort into the habitats commonly used by these species in winter. For
example, although brown lemmings tend to concentrate in wet sedge meadows during summer,
they typically move to drier grounds such as mesic tundra for the winter (Duchesne et al.
2011b). Otherwise, it would be preferable to cover all potential habitats in our study area until
you get a better feeling of their winter distribution. Whenever possible, it is also best to monitor
the same transects or plots/grids every year to allow comparisons over time.
Transects should be
surveyed following the
method described in Section
2 above. The formal line
transect method described in
that Section is particularly
well suited for sampling
winter nests. Note that when
applying these techniques to
winter nests, the term
“element” used in Section 2
will here refer to individual
winter nests.
Line transects are best for long-term monitoring because they can cross a greater variety
of habitats than plot/grid sampling. This approach is also more likely to provide good results for
a reasonable sample size. However, if live trapping is already planned at your study site,
surveying winter nests in the trapping grids as well would be ideal. Everytime you encounter a
winter nest during a survey, you should:
Assign a unique individual number for all fresh nests* found during your survey
For transects: record the GPS location and the perpendicular distance of each nest to
the transect line (see Section 2.1 for more details).
For grids: record the GPS location of each nest (see Section 2.1 for more details).


© Dominique Fauteux
18
All fresh nests should be brought back
to the camp or laboratory in a plastic
bag identified with the date, the nest
and transect/plot numbers for further
analysis (see Section 6.4 below).
Old nests encountered during your
sampling should also be noted and
removed/destroyed to avoid counting
them again in the future.
If nests cannot be processed right
away back to the camp, they should
be transferred into a labelled paper
bag and put in an oven to dry at 50°C
for at least 48 hours to prevent them
from rotting before they can be
examined.
* TIPS!
       -

    
  
     
 

     
      
       

      
    
 
     
      


© Dominique Fauteux

19

In years when small mammal abundance is low and very few winter nests are found along
transects or on grids, collecting nests found opportunistically while walking in the field can also
be useful to improve the precision of certain measurements. Although using these nests to
determine annual abundance is not recommended (because they were not found using a
systematic sampling design), they can provide additional information on reproductive activity
or predation rate (see 6.4). The location of all fresh nests found opportunistically is also
recorded with a GPS receiver for future reference. These nests should also be brought back
from the field and their content analysed just as those found along transects or on plots.

Nest surveys are best done as soon as possible after snowmelt (early in summer), since
high winds can blow the nests around after snow melt. Rain will also flatten and discolor nests,
which will make identification of fresh vs old nests more difficult.

50 or 100-m measuring tape
GPS receiver
Plastic bag, label and permanent marker
Small plastic tray of pale colour to examine content of winter nest (if done in the field)
 

Winter nests left behind by small mammals can provide precious information such as the
species using the nest, the occurrence of reproductive activity or predation by weasels. This is
usually determined based on hair, faecal material and bones or carcasses found inside nests.
This is why all nests should be torn open to look for these signs. It is best to open the nests on a
pale coloured plastic tray to sort through the debris for signs.
Note that when you have gained enough experience at identifying these clues, nests can
be dissected directly in the field rather than in the laboratory. All nests processed in the field
should be completely ripped apart to avoid recounting them the next year.
Here is a summary of the information that should be gathered when examining the
content of winter nests. See also Section 10 for additional details.

Small mammals spend a lot of time in their nests during winter and you will typically find
high amounts of droppings inside them or just around it in the field. If a large pile of faeces is

20
present just outside the nest, you should collect
them along with the nest. Droppings from each
nest should be carefully examined.
The two lemming species can be identified by
examining the size, color, shape and form of
droppings (see Section 10 for details). Note
that two different species sometimes use the
same nest, and thus you may occasionally find
nests with both types of faeces.
The reproductive activity can also be derived
from the size of faeces from the same species:
smaller droppings indicate the presence of
young* in the nest at some point over the
winter. If >20% of all droppings examined (in
this case, a minimum of 30 faeces should be
examined (Duchesne et al. 2011a) are
considered to be from young, then the nest can be categorised as having been used for
reproduction. Otherwise, it is not conclusive and the nest should be rated as non-
reproductive.

The presence of bones or body remains of small mammals inside the nest are a sure sign of
predation. Fur attached on skin can also be found in nests but these are more subtle to find.
In rare cases, intact, newly born but dead lemmings may be found in nests. This can occur
either because the mother abandoned the young (possible in young females) or it was killed
outside the nest. In this case, it is not clear if predation occurred or not even though
recording this information is useful.
Jaw bones, if present, can provide additional cues to identify species. Each species of small
mammals has its own unique set of dentition (see details in Section 10). If carcasses are
present and complete enough, it can also help the identification through other external
characteristics unique to each species.


* TIPS!
youngadults
Droppings from young            
droppings of adults    


© Dominique Fauteux

21

Small mammals moult during
winter and by moving inside the nest
they sometimes leave a thin and very
sparse layer of hair covering the walls
of the nest cavity. However, when
weasels kill small mammals in the
nest, they often line the nest with hair
removed from the carcass. Therefore,
a thick layer of hair tufts, which is
easy to distinguish from the sparse
layer of hair due to the moult of the
animal, is a sure sign of predation by a
weasel (or ermine)*. This is important
information and should be noted.
The microscopic cuticle patterns
of hairs can in principle provide
additional criteria to identify the
species through. However, this can be
tricky for the untrained person and it
requires a set of hair collection for
comparison as well as a microscope.
This technique is beyond the scope of
this manual and will not be discussed
further.
* TIPS!
      

         
     
     
 
       
      



Pros
Cheap, relatively easy and quick
to do
Very good estimate of winter
abundance
Give information on reproductive
activity and weasel predation
Not necessary to kill or capture
animals
Cons
Provide no information of timing of
use during the winter
Some nests cannot be identified to
species due to the lack of faecal ma-
terial in them
Nests sometimes used by more than
one species (impossible to know
who built it)
© Dominique Fauteux

23

Museum Special® and Victor® traps are two models
of snap traps designed in the same way and are commonly
used to trap small mammals. The bait pedal acts as the
release mechanism. When a small mammal starts to feed on
the bait the metal arm is released and the animal is killed
instantly by cervical dislocation. The efficiency of each trap
depends on the size of the species of interest. Generally, a
bigger trap will be more efficient at capturing larger animals.
Victor® traps come in 2 different sizes designed to capture
primarily small house mice or large rats while the Museum
Special® trap falls in between. The latter has been used
extensively in ecology and is often recommended as the best
option to trap lemmings and voles. However, they are
becoming more difficult to find on the market.

1. Sampling small mammals using snap traps is done using trapping lines, which are
analogous to transects. The goal is to cumulate a trapping effort* of at least 500 trap-nights
per trapping sites. Trapping should occur over a period of 3 to 4 days. Using longer periods
is not recommended because since this method removes animals, you may start depleting
the population after a few days, which would reduce trapping success in subsequent days/
weeks. Therefore, achieving 500 trapping-days over 3 days would require setting up about
170 traps each day. It is recommended to use the same trapping sites every year to allow
for comparison. Trapping site selection
Choose sites that cover all potential small mammal habitats. For example, during
summer brown lemmings prefer wet habitat while collared lemmings prefer dry
* TIPS! ‒ Trapping effort
trapping effort -

-
              


© www.woodstream.com
© www.victorpest.com


24
habitat.
2. Setting trap lines
The number of trap lines can vary from 2 to 4 depending on the size and shape of the
habitat patch. Lines should be laid parallel to one another with a minimum distance
of 100 m between each other. Trapping stations are staked out every 15 m along each
trapping lines. Record the GPS position of each station for future references.
If the number of traps available for the survey is limited, each trapping line or group
of lines can be set and baited one after the other. For example, set traps along 2 lines
for 3 days and then move the traps to the next set of 2 lines for another 3 days.
3. Setting traps
Each station consists of 3
snap traps within a 2-m
radius of the station. Each
trap is attached to the station
with a 2.5-m string to avoid
them being carried away by
other animals passing by.
The 3 traps should be spaced
out as much as possible and
placed at sites with fresh
signs of small mammal
activity such as runways,
burrows, fresh faeces or
grass clippings whenever
possible. Using more than
one trap per station is
recommended to avoid local
saturation because once an
animal is caught, a trap is no
longer available to catch
other animals passing by
until it is reset the next day.
Traps are placed flat on the ground and clear of any vegetation that could interfere
with the trap operation. If the mechanism is blocked by the vegetation, the animal
may only be injured and suffer unnecessary pain. Make sure traps can be located
again. If the bushes are thick, putting a flag tape above each trap could be useful!
4. Baiting traps
Each trap is baited with a big pea-sized amount of peanut butter mixed with rolled
oats. Flour can be added to the mixture to reduce the stickiness of the bait which
makes it easier to clean traps afterwards.
-


© Dominique Fauteux
25
5. Checking traps
Ideally, traps should be checked once per day, at 24-hour interval, preferably early in
the morning.
If an animal (small mammal or
other) is caught, you should
first put on nitrile surgical
gloves to avoid disease
transmission. The animal is
then collected and the following
data needs to be recorded: the
trapping line and station
number, habitat, species,
weight, age group (adult or
juvenile) and sex (see Section
10 for criteria to identify
species, age and sex). Re-bait
and re-set the trap.
If the animal captured cannot be properly identified in the field (or if there are any
doubts), it should be brought back to camp (or laboratory) in a ziploc bag identified
with the trapping line and station number for further analysis.
In case of a misfire* (i.e. trap is sprung but no animal was caught) it is important to
also record that information as well as the trapping line and station number.

* TIPS! ‒ Misfires
Misfires 

             

    


 



                



© Dominique Fauteux
26
In case of accidental captures (other species than a small mammal), the information
should also be recorded along with the trapping line and station number.
On the last day of trapping, traps are collected from the field and cleaned of any
remaining peanut butter before being stored until next season to avoid rotting of the
bait.
An excellent document showing in details how to set and run a snap-trap line for small
mammals has been produced by the Government of the Northwest Territories and could also be
consulted (ENR 2005c).

Snap trapping should be conducted once per summer, ideally in mid to late July. In some
species, especially lemmings, it is not recommended to do trapping at the end of the summer
(e.g. August) because populations often start to decline by then.

Field book and pencil
Field guide to small mammals
GPS receiver
Measuring tape
Nitrile gloves
Peanut butter mixed with rolled oats for baits (prepared in advance)
Portable spring scale (with a weight capacity adapted to the species of interest)
Roll of string
Snap traps
Wooden stakes
Ziploc bags and permanent marker

27
Pros
Give a good and precise estimate
of abundance
Can provide additional data on
parasites and reproductive
conditions through dissection
Cost and time efficient
Cons
Kill the animals captured
Ethic concerns in some jurisdictions
Capture of non-target species can
occur
Opportunistic predators can steal
carcasses from the traps
Museum Special traps are hard to
find in Canada nowadays

29


The two most common live traps used to capture live small mammals in North America
are single-capture Sherman® and Longworth® traps. Multiple-capture live traps also exist
(such as the Uglan trap commonly used in Scandinavia) but their large size makes them incon-
venient for transportation and their effectiveness is not necessarily higher than single-capture
live traps. We will thus not discuss them any longer. Sherman® traps come in 3 sizes (small,
medium and large) and are often used to capture mice and voles while Longworth® traps are
one size only but are suited to capture most species of small mammals (lemmings, voles and
mice). The door of these traps is triggered when the animal goes far enough inside the trap and
its weight releases the latch that holds the door open (i.e. a small horizontal rod in the Long-
worth trap entry tunnel or a pedal in the middle of the Sherman trap). Each model of traps has
its advantages and disadvantages but, overall, the Longworth® should be preferred (especially
for lemmings) when possible.

Costly to purchase (40$ or more per trap)
Not collapsible, bulky to carry in the field
Trap door can be locked open easily between
trapping session, allowing pre-baiting
Provides more space and comfort for the ani-
mals in the trap
Misfires rarely occur
Bait and bedding do not interfere with trigger
mechanism

© www.nhbs.com


Cheap to purchase (~25$ for a large
trap, ~19$ for a small trap)
Collapsible and easy to carry in the
field
Trap door cannot be locked open
More prone to misfires
Bait or bedding can sometimes interfere
with the trigger mechanism
© www.forestry-suppliers.com

30

Pitfall traps basically consist of a hole in the ground into which unwary animal falls.
These traps are homemade and usually consist of a metal can or a plastic bucket buried into the
ground so the rim is flush with the surface. The size and the depth of the hole depend on the
target species. The pitfall trap has to be big enough so that the animal is unable to crawl or
jump out of the hole. Generally, they are at least 40-50 cm deep and 20-40 cm in diameter. To
protect the captured individual from rain, sunlight, exposure and predators and to reduce
mortality, a cover is often added on top of the hole. The cover should be larger than the trap
opening to prevent runoff into the trap and propped by rocks or other material to allow for a
space (~10 cm) between the cover and the rim of the bucket. Holes should also be drilled at the
bottom of the can or bucket to help drain any water that would accumulate in the trap. Note that
small rodents will often try to bite through the holes to find their way out of the bucket. It is
thus imperative that if holes are made, it should be in a bucket made of sturdy material (e.g.
avoid flimsy plastic). A piece of bait should be placed in the pitfall trap as well as bedding
material to increase the comfort of animals.
© Dominique Fauteux
© Dominique Fauteux

© Hoekstra et al. 1977 © Dominique Fauteux
 

31

-
Ear-tags are the most common marker used in small mammal live trapping studies. It is a
small aluminum marker that is put on the animal’s ear flap (similar to an earring) with specially
designed pliers. It usually has a unique 3 to 4-digit code stamped on one side of the tag to
identify the animal if it is recaptured later.

A PIT tag is a small chip about the size a rice grain that is injected under the skin of the
small mammal using a specialized syringe. This chip does not require any batteries. It is
energized by an electromagnetic field produce by the PIT tag reader. It also has a unique code,
usually 10-digit long. This type of chip was first used in research to study fish movements but it
is now widely used by biologists for mammals, birds, reptiles and amphibians. It is also used by
veterinarian to identify household pets as well as for tracking zoo animals and livestock.
© Dominique Fauteux
© www.nationalband.com



© Guillaume Slevan-Tremblay
-

© Marie-Christine Frenette
© www.fishbio.com

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
-
Cheap to purchase (~15$ for 100 tags)
Difficult to put on some lemming species
due to small ear size
Animals can lose tags if they get caught in
vegetation or roots in burrows (especially
in lemmings due to small ear size)
Some individuals may try to remove the
tag by themselves
Tag code can be misread due to the small
size of the marker

Sampling small mammals using live trapping is usually done using square grids. The
standard size of trapping grids is usually 100 trapping stations (10×10). However, the use of
larger (144 stations, 12×12) grids in areas where small mammal density is low is recommended.
Conversely, smaller grids (64 stations, 8×8) may be used if animal density is high or if
resources are limited, but this may result in a loss of accuracy. It is best to use the same trapping
sites and dates every year to allow comparison. Trapping sessions usually last 3 days, which
would yield 6 visits per session when traps are checked twice a day (see Table 8.1).

Costly to purchase (~800$ for 100 tags)
A PIT tag reader is needed to identify
the animal
Tag code can sometimes be misread
due to the length of the code and the
mix of numbers and letters involved
If injected properly, they cannot be lost
(injuries are extremely rare)
Easier to install on the animal than ear-
tags
Can be re-used if tagged animals acci-
dentally die in traps (the tag is then re-
trieved by dissection)
 
Day 1 - 8:00 Set & bait traps
Day 1 - 20:00 Visit #1
Day 2 - 8:00 Visit #2
Day 2 - 20:00 Visit #3
Day 3 - 8:00 Visit #4
Day 3 - 20:00 Visit #5
Day 4 - 8:00 Visit #6 & trap closing
Example of trapping schedule within a 3-day session.

33
®®
1. Setting traps
Set up the trapping grid lay out in the field with a stake at each station (see Section
2.2 above).
Place one trap near each station. Carefully search the area around each station for
fresh signs of activity such as an active burrow or runway. If you find a good runway,
place the trap on the runway. If there is a burrow, place the trap in front of the
entrance but do not block the entrance. If there is no sign, place the trap under cover
(when possible).
The distance of the trap from the station stake should not exceed half of the distance
between stations (e.g., if grid markers are every 20-m, the trap should not be farther
than 10 m from the station stake).
The station number (letter-number) should be indicated with a permanent marker on a
duct tape sticked to the trap in case any confusion arises during subsequent visits as
to which station a trap is associated to.
Bait the tap (see below), open the door and set the triggering mechanism. Make sure
that the bait has not rolled over the trigger while setting the trap.
Make sure the trap is stable and flat or lightly inclined forward (never inclined
backwards!) to avoid any accumulation of water in the trap during rainy days. When
possible, the traps should also be oriented opposite to the dominant wind. The
entrance of the trap should not hang in the air: it has to be on flat ground.
2. Baiting traps
Line the back of the trap with a handful of synthetic bedding for nesting material. Use
just enough to create a warm nest but not too much that the animal might view it as a
blockage as opposed to nesting material.
Place the bait in front of the bedding material: add one piece of apple (~¼ of a large
apple) for water. A small pea-size ball of peanut butter mixed with rolled oats can
also be added.
3. Checking traps and manipulating animals
Traps should be checked at least twice daily at 12-h intervals, early in the morning
and in the evening. During hotter and colder days, it might be best to check traps
every 8 hours.
If an animal is captured, you should first put on nitrile surgical gloves to avoid
disease transmission. Indeed, some diseases borne by small mammals can be
transmitted to humans and some cases have been reported in Scandinavia and
southern Canada.
The animal should be transferred into a clear and strong plastic bag. Place the bag
around the trap and make sure there is no opening where the animal could escape.

34
Open the trap in the bag and allow
the animal to fall in it before taking
the trap out of the bag.
Handling a small rodent is usually
done by grabbing the abundant skin
found behind the neck between the
thumb and the index. People doing
this for the first time should practice
until being comfortable. This will
help avoid injuries for both the
handler and the animal and will
speed up the manipulations, which
means less stress for everyone.
For each capture, you should:
A. Weigh the bag with the animal
inside with a spring balance
B. Remove the animal from the
plastic bag by grabbing it by the
nape of the neck and check if it
already has a marker (visually
for ear-tags or with a scanner
for PIT tags). If it is a marked
individual, record the code in
your field book (always check
it twice, misreading is the most
common error in the field with
these types of markers). If it
does not have a tag*, it needs
to be marked (see below,
“Marking animals”).

* TIPS! ‒ Torn ears
       -     

     -     
           



© Dominique Fauteux
© Guillaume Slevan-Tremblay




35
C. Identify the animal captured to the species level (see Section 10.1. below for
criteria)
D. Determine the sex of the animal (see Section 10.2. below for criteria)
E. Determine its reproductive condition (see Section 10.3. below for criteria)
F. Determine its age group (adult or juvenile) (see Section 10.4. below for criteria)
G. Weigh the bag and subtract from the initial weight of the animal with the bag to
obtain the weight of the animal itself.
After completing all the previous manipulations, release the animal. You then need to
clean the trap, add new bedding material and a fresh bait and reset the triggering
mechanism.
If an animal is found dead in the trap, check it for the presence of a tag and record the
rest of the data as if it was a live capture. Also record any information that could help
determine the cause of death. Is the bait consumed? Is there a lot of faecal material in
the trap? Is there any apparent wound on the animal’s body? Is the animal’s fur
completely wet or is it dry?
If you come upon a trap with a closed door but no capture (misfire), make sure the
release mechanism is set properly. Check that the bait is still present and the bedding
material is dry. If not, replace the synthetic bedding, put fresh bait and reactivate the
trap.
On the last trap check of a 3-day trapping session, you must decide if traps are to be
removed or left in place. If other trapping session will be done later in the season, the
traps can be locked open (only possible with in Longworth® traps) during the
interval or closed (for Sherman® traps). If no more trapping will be done that year,
then all traps should be collected, brought back to camp and cleaned thoroughly
before storing them until next season.
On the last visit of the last trapping session for the season, any new, unmarked animal
does not need to be tagged but you do need to record all other information about its
capture before releasing it.
4. Marking animals
With ear-tags:
Locate its  ear and place the ear tag at the base of the ear flap, near the skull
Make sure the tag pointed end has pierced through the ear flap, passed through the
tag hole on the opposite side and folded over properly (check each tag alignment
before placing in the pliers). Be careful not to clamp too much skin in the tag
(increased risk of infection) but place the tag far enough into the ear so that it does
not easily rip out*.
 in your field book.

36
With PIT tags:
Sterilize the end of the syringe needle with an antiseptic wipe as well as the PIT tag
and insert the tag in the needle.
While holding the animal by skin of the neck, insert the needle into the loose neck
skin, under your finger, and inject the tag under the skin. Care should be taken not to
insert the needle too far in the body, which could cause internal injuries to the animal.
Make sure that the PIT tag has been injected properly and does not stick out of the fur
when you remove the needle.
Scan the lemming with the PIT tag reader to double-check that it is inside the animal.
 in your field book.
Another excellent document describing the methods of setting a live-trap transect or plot
has been produced by the Government of the Northwest Territories and could also be consulted
in parallel with the current text (ENR 2005b).

For pitfall trap sampling, it is recommended to use trapping lines (minimum of 10) with at
least 5 stations per line separated from each other by at least 60 m. It is best to use the same
trapping sites and dates every year to allow comparison. Trapping sessions should last between
2 and 6 days depending on how many animals are captured.
1. Setting traps
Once the trapping lines are staked out, place a pitfall trap in a 10-m radius from each
station, preferably at the intersection of 2 to 3 small mammal runways. Make sure the
hole is deep enough so the top of the trap is flush with the ground and that it does not
create an obstacle because animals should not have to climb.
2. Baiting traps
Put a handful of bedding material at the bottom of the trap.
* TIPS! ‒ Ear-tagging lemmings
Collared lemmings 
     -        
                
       
brown lemmings voles
             


37
Add one piece of apple (~ ¼ of a large apple) for water. A small pea-size ball of
peanut butter mixed with rolled oats can also be added.
Don’t forget to replace the trap cover to provide shade and protection for captured
animals. If needed, put a rock on top of the cover to avoid it getting blown away.
3. Checking traps, manipulating and marking animals
Follow the same procedure as described for the Longworth®/Sherman® traps above.

If only one live-trapping session can be done during the summer, we recommend
conducting it in mid-summer (mid to late July) because in some species (especially lemmings)
populations often start to decline by the end of the summer (August). Trapping can be
conducted twice or three times during the summer if resources allow it. In that case, trapping
sessions should be spaced out as much as possible. With two trapping session, the first one
should be conducted in early summer (e.g. June), soon after snow-melt and the second one in
late summer (e.g. August or September). If a third one is possible, it should be half-way
between the two other sessions. Having more than 1 trapping session per year will allow
tracking seasonal change in small mammal abundance and estimation of their survival rate (an
important demographic parameter) based on the recapture of marked individuals between
trapping sessions.

When setting up a trapping grid:
50-m or 100-m measuring tape
Apples (cut in quarters) and peanut butter mixed with rolled oats (prepared in advance) for
bait
Bamboo sticks to mark trapping stations
Duct tape and permanent marker
Field book and pencil
GPS receiver
Live traps
Metal labels
Synthetic bedding
Wooden stakes to mark corners of the
grid and beginning/end of lines
© Dominique Fauteux
-

38
Pros
Provide the best abundance
estimate without affecting the
population for future surveys
Captured animals captured can
be easily identified at the species
level
Provide considerable information
on population structure such as
sex, age group, reproductive
condition and body weight
Mortalities are minimized with
baits and bedding
Method most often used for
intensive ecological studies
Cons
Costly material but cost is
variable depending on traps and
tagging method chosen
Require relatively large time
commitment
Require training for handling
small mammals
Require training for correctly
identifying reproductive
conditions with external traits
only
Potential ethical issues
(accidental mortalities)
During trap visits:
Antiseptic wipe (e.g. benzalconium
chloride) to clean syringe needle and
PIT tag before injection
Apples (cut in quarters) and peanut
butter mixed with rolled oats (prepared
in advance) for bait
Blunt tweezer (for marking collared
lemmings with a ear-tag)
Field book and pencil
Field guide to small mammals
GPS receiver
Garbage bag
Knife to clean traps
Permanent marker

PIT tag syringe or tagging pliers
PIT tag reader
PIT tags or ear-tags
Portable spring scale (100 g scale
ideally)
Strong Ziploc® bags for weighing
and for accidentally killed animals
Synthetic bedding
39

In the past 20 years, cameras automatically
triggered by movements have been used extensively by
hunters to track big game animals in their territory but
they have also been used increasingly for monitoring
wildlife. Infrared beams can detect movements during
either night or day and trigger the camera to take
pictures or videos. Cameras can also be programmed to
take pictures at fixed intervals. Very large number of
pictures can be accumulated over relatively short time
periods though battery life and disk space will usually
limit the number of pictures that can be collected. This
is a modern, non-invasive technique to monitor wildlife
over a wide range of condition. In some areas,
automated cameras became the best tool to detect rare
species such as large felines in tropical areas. Most
cameras also have an infrared flash, which allows
pictures to be taken in the dark. However, their lack of
specificity regarding what is being photographed and
the general absence of marks to differentiate individuals on pictures makes the technique less
precise than traditional trapping methods to estimate abundance.
Cameras used for this type of monitoring are now manufactured by several companies:
Bushnell®, RECONYX®, Acorn®, Spypoint®, etc. They are sometimes called «game
cameras» or «trail cameras». We recommend RECONYX® or Bushnell® because they proved
to be durable and we had good experience with these brands. These cameras are fairly rugged
and can endure rough weather conditions, including the extreme cold of the Arctic winter.
However, good cameras are relatively expensive, which makes this method less affordable for
many projects involving wildlife monitoring. There is a wide price range for such cameras,
usually from 100$ to 600$ per camera. However, additional expenses have to be considered for
the memory cards to store pictures, the batteries, and physical supports (e.g. tripods) to deploy
the cameras in the field.

In order to conduct small mammal survey with automated cameras, we suggest deploying
cameras in suitable habitats, either systematically (i.e. at fixed distance) or randomly across
your study area. As this is still an experimental method that has not been used frequently with
small mammals yet, it is difficult to provide more detailed recommendations on a specific
sampling design. This method should be most useful to provide information on sites that are

© RECONYX



40
occupied by small mammals, the timing of occupancy, species involved and perhaps a relative
index of abundance.
Cameras can provide information on small mammal activities during both summer and
winter. However, some aspect of camera deployment will differ between these two seasons
because in winter small mammals spend almost all their time under the snow. Therefore, this
must be considered.

1. Preparing the cameras
Before installing a camera in the field, it should be tested first to make sure that the
mechanism is working properly and that pictures are correctly saved on the memory
card.
Select in advance sites to deploy cameras in suitable habitat patches based on
information available in the literature and by studying maps or by going directly in
the field to validate the information.
2. Installing the cameras
Each camera should be set in an area
showing sites of use by small mammals
(e.g. runaways, faecal deposit, runaways)
near each pre-selected site. The position of
each camera should be recorded with a
GPS receiver and marked with a
permanent stake. For monitoring purpose,
the same sites should be used over the
years to allow comparison over time.
Cameras should be placed near the ground
and aimed toward the area showing signs
of use by small mammals and where plant
cover will interfere minimally with the
pictures. Cameras should be slightly tilted
towards the ground to detect small
mammals and avoid activation by non-
target species such as foxes and birds.
Some highly sensitive cameras may be
triggered by vegetation blown by the
wind.
Tripods or any other devices supporting the cameras should be firmly anchored to the
ground by steel wires and large nails or pegs for protection against strong winds and
© Dominique Fauteux




41
disturbance by large wildlife. The cameras should also firmly fixed to tripods to
ensure that they do not move under strong wind.
3. Using baits
To increase detection of animals, especially when abundance is low, baits can be
used.
Baits should be protected from non-target species and thus placed into a container
that cannot be accessed by other animals. For instance, baits could be placed in the
middle of PVC tubes (5 cm diameter, ~30 cm long). Care should be taken to ensure
that animals entering by either end of the tube can be detected by the camera. A more
expensive alternative could be to build small boxes made of clear plexiglass, which
would allow observing the animal inside the box.
Baits should be added every week or whenever it has been depleted to ensure
continuous sampling.
Peanut butter mixed with rolled oats and flour should be used as potential bait
because it is rich and should last for several days before being depleted.
4. Operating and retrieving the cameras
Once the camera is installed, it should be activated with the required mode. Some
modes include rapid photography so that 3 or more pictures are rapidly taken every
time a movement is detected. New cameras can also capture videos of the detected
animal.
Your programming should take into account the size of your memory card, the
autonomy of your batteries and the frequencies at which cameras are visited to
replace cards and batteries.
When the survey is completed, cameras should be removed from the field and safely
stored.
All pictures taken by the cameras should be analysed and each time one small
mammal is detected, it should be identified to species and entered into a database.

This method has recently been used successfully to monitor small mammals under the
snow in northern Norway (Soininen et al. 2015).
1. Preparing, operating and retrieving the cameras
Follow the same approach than for a summer deployment. However you should
consider that during winter you may not be able to access the cameras as often.
Therefore, you should program your cameras to ensure that the number of pictures
taken does not exceed the capacity of your memory card or does not drain your
batteries too rapidly. High capacity batteries such as lithium batteries must be used in

42
winter even tough they are more expensive.
2. Preparing, operating and retrieving the cameras
During winter, cameras must be installed in enclosed boxes. These boxes should be
deployed in habitat suitable or lemmings such as snow beds where signs of winter use
have been detected. Boxes and cameras should be installed in late summer/early fall,
before the snow sets in.
Boxes originally designed to trap
lemmings under the snow can be
used to set cameras (Bilodeau et
al. 2013). Small mammals can
enter these boxes through PVC
tunnels on either side of it and
may even use them to build
winter nests (see photo on the
right). Cameras are set in the
upper portion of these boxes,
which have a chimney-like shape
and aimed toward the bottom of
the box to detect animals entering
the box. Because focal distance is
very short (~30 cm), care must be
taken that the focus of the camera
is adjusted accordingly, otherwise
picture will be blurred. For a
slightly different system, see
Soininen et al. (2015).

A computer
Automated cameras
Batteries for the cameras
Field book and pencil
GPS receiver
In winter, wooden boxes of appropriate shape and size
Memory cards for the cameras
Memory card reader for the computer
Physical supports (e.g. tripods, steel T-bars)
© Dominique Fauteux


43
Pros
Automated system with a high
detection capacity
Provide species-specific
estimation of occupancy
Can be used during any season
Require a low time investment
once installed
Not necessary to kill or capture
animals
Cons
Costly but variable depending on
type of camera
Allow only a gross estimation of
abundance
Pictures not always clear and
sometimes blurry due to
movement (hard to identify
species)
Subject to weather problems
affecting visibility
PVC tubes and baits (if applicable)
Steel wire with pegs

45

Small mammals can be identified at the species level using several external
characteristics, most of which can be applied directly in the field though others require more
equipment (e.g. stereomicroscope to look at molar patterns of enamel) or dissection of the
animal. It is always best to identify an animal based on more than one characteristic because
some may be shared by more than one species. A good field guide of small mammals for your
study area is always a good tool to start getting to know your potential captures. The Northwest
Territories government (ENR 2005a) also produced a good document to identify northern small
mammals
More than 15 species of small mammals have been surveyed in Nunavut and the
Northwest Territories, though only a few species are commonly found (see Appendix). In
Nunavut, only two species are common in the tundra: the brown lemming and the collared
lemming. In this manual, we will focus primarily on criteria to distinguish these two species and
to identify the sex, age and reproductive condition. The latter criteria, however, are not unique
to these two lemming species and may be relevant to other lemming or vole species.


(Dicrostonyx groenlandicus)
Winter: white coat; Summer: Back brownish-
black with some buff,   
    commonly found,
creamy-buff below.

(Lemmus trimucronatus)
Head greyish, reddish-brown back and
rump; underparts creamy to medium brown.
    
.



© Université Laval
© Université Laval
46
© Dominique Fauteux
© Dominique Fauteux

(Dicrostonyx groenlandicus)
and 
Soles of the feet are ; third and
fourth fore claws .
Adult droppings -long; often 
at one or both extremities; generally 
.

(Lemmus trimucronatus)
and round;  through the
fur
Fore claws of .
Adult droppings -long;  at
both extremities; generally -.



© Christine Lambert

© Frédéric Bilodeau
© Guillaume Souchay
© Guillaume Slevan-Tremblay
© Guillaume Slevan-Tremblay
47

When animals are found dead in the field it is also possible to identify them at the species
level using their teeth. The animal must be dissected in the laboratory and its jaw bones are
extracted to get a better view of the pattern of its dentition. Teeth need to be examined at least
with a good magnifying glass or a stereomicroscope (10x to 40x). Figure 10.1 shows examples
of one collared lemming and one brown lemming.

The gender of small mammals is fairly easy to determine. When the animal is grabbed by
the nape of the neck (see Section 8.3 above), you can examine its ventral area to determine its
sex. With your free hand, grasp and gently pull back its tail and hind feet to examine its external
genitalia.

© Dominique Fauteux




m3 m2 m1
m1
m2
m3
Anterior (incisors)
Posterior (throat)
Labial side (lips)
Lingual side (tongue)

Presence of a penis and scrotum
Distance between the anus and penis
relatively long
In some males, the testicles will be
pulled back inside the abdomen.

Presence of a urethral papillae (not to be
confused with the penis)
Presence of a vaginal orifice
Distance between the anus and vaginal
orifice relatively short
48 
However, a small crest of skin (scrotal
septum) running from the penis to the
anus can be seen
In young males, the scrotum is hard to
discern but the scrotal septum can be
seen when pulling the tail dorsally
Presence of 2 rows of nipples on
abdomen (as the nipples are hidden in the
dense fur, it is best to blow air with your
mouth on the abdomen of the animal to
raise the hair and expose the nipples
In young females, the vaginal orifice is
closed but the absence of a scrotal
septum (present only in males) when
pulling the tail dorsally can be the best
evidence
Urethral papillae
Penis
Scrotum with
testicles
Anus
Vaginal orifice
© Christine Lambert
© Yannick Seyer

Within the same species of small mammals, the size of an individual is not an absolute
criterion to decide of its ability to reproduce because sexual maturity can be achieved before or
after adult body size is reached. The sexual maturity of individuals and thus their ability to
reproduce must be determined based on the condition of their reproductive organs. When an
animal is captured, you should try to categorize the animal into one of the following
reproductive condition:

1. Immature;
2. Mature with perforated vagina only;
3. With enlarged nipples (lactating);
4. Pregnant.

1. Immature;
2. Mature with empty scrotum (abdominal
testes);
3. Mature with testes in scrotum.
49

Perforated vagina
The vagina is perforated when the hymen is gone and the vaginal orifice is ‘open’ (see
arrow on the picture below). When the vaginal orifice is ‘closed’ it is almost invisible and the
female would then be considered as non-reproductive (typically occurs in immatures but can
happen in adults too).
Pregnant
In small mammals, the uterus presents itself as 2 horns (see arrows in picture below) in a
V shape at the base of the abdomen. When a female is pregnant, you can feel the foetuses as
small bumps when you  feel the base of its abdomen, near the thighs. Pregnant females in
advanced states will also have a conspicuously large abdomen.
Lactating
A female is considered as lactating if she is showing
enlarged nipples on her abdomen. Enlarged nipples will be
protruding from the skin of the animal whereas nipples of non-
lactating females will appear as small dots on the skin. Because
of the dense fur coat of lemmings, it is important to blow air on
the abdomen with your mouth to expose the nipples.


© M.J. Cook, 1965
© Dominique Fauteux
© Christine Lambert



50
© Christine Lambert

Scrotal testes vs. abdominal testes
In males, the only way to determine its reproductive status is to examine the region
between the anus and the penis. Testes are considered ‘scrotal’ when they are prominent, well
defined and inside the scrotum.
When testes are ‘abdominal’, the scrotum is well-developed but it is flat and empty.
Palpating this body region (see picture below) is the only way to know if the scrotum is empty
or not.
--
If an animal does not fall into any of the conditions described above then it is considered
non-reproductive. For some young individuals, their sex may be difficult to determine.
In young and non-reproducing males, the scrotum is difficult to see unless air is blown on
the lemming fur. When the tail is pulled back you can sometimes see a thin line on the skin
connecting the anus and the penis (see arrow on picture).
In young or non-perforated females (i.e. non-reproductive), it is also possible to observe a
short line perpendicular to the anus-vagina axis at the base of the urethral papillae. This short
line is the vaginal orifice that may still be closed due to the immature state of the animal or the
absence of intercourse.


© Yannick Seyer
51

A small mammal can be classified in two age groups, ‘adult’ or ‘juvenile’ (or young)
based on 2 types of information: its body weight and its reproductive condition. These two
criteria can often be collected and used together to age an animal captured during snap trapping
or live trapping surveys.

On Bylot Island (NU), we have been live trapping brown and collared lemmings for more
than 10 years and based on the body weight* recorded for each animal captured over the years,
we have been able to develop a criteria (Table 10.1) that can accurately determine age* group
for about 95% of the individuals in the field (Fauteux et al. 2015):

-
© Christine Lambert
* TIPS! ‒ Relative age determined by weight
Body weight      
             

           

             


-

There are always exceptions to every rule and occasionally the reproductive condition can
overrule the age group of a captured individual when it was previously determined based on its
body weight. As mentioned in Section 10.3, an animal can attain its sexual maturity before it
has reached its adult size. However, certain reproductive conditions can only be associated to
adults. These are: lactating female, pregnant female and male with scrotal testes (see Table 10.2
for more details).
  
Female Juvenile <28 g Juvenile <40 g
Adult ≥28 g Adult ≥40 g
Juvenile <30 g Juvenile <40 g
Male Adult ≥30 g Adult ≥40 g


 
   
Non-reproductive X X X X
Perforated vagina X X
Lactating X
Pregnant X
Scrotal testes X
Abdominal testes X X
 Possible age group association according to the reproductive condition
Age classes of lemmings according to body weight
53
Bilodeau, F., A.J. Kenney, B.S. Gilbert, E. Hofer, G. Gauthier, D.G. Reid, D. Berteaux, and C.J. Krebs.
2013. Evaluation of a technique to trap lemmings under the snow. Arctic 66:32-36.
Duchesne, D., G. Gauthier, and D. Berteaux. 2011a. Evaluation of a method to determine the breeding
activity of lemmings in their winter nests. Journal of Mammalogy 92:511-516.
Duchesne, D., G. Gauthier, and D. Berteaux. 2011b. Habitat selection, reproduction and predation of
wintering lemmings in the Arctic. Oecologia 167:967-980.
ENR. 2005a. NWT Small Mammal Identification. GNWT. 27 pp. Available at http://www.enr.gov.nt.ca/
sites/default/files/documents/small_mammal_identification.pdf
ENR. 2005b. Small Mammal Trapping (Live Trapping). Film script prepared by Outcrop Communica-
tions for ENR, GNWT. 20 pp. Available at http://www.enr.gov.nt.ca/sites/default/files/documents/
live_trapping.pdf
ENR. 2005c. Small Mammal Trapping (Museum Special Traps). Film script prepared by Outcrop Com-
munications for ENR, GNWT. 18 pp. Available at http://www.enr.gov.nt.ca/sites/default/files/
documents/museum_special_traps.pdf
Fauteux, D., G. Gauthier, and D. Berteaux. 2015. Seasonal demography of a cyclic lemming population
in the Canadian Arctic. Journal of Animal Ecology 84:1412-1422.
Hoekstra, B., E. van der Straeten & V. van Laar. 1977. Population research on terrestrial mammals in
the Benelux. Wetenschappelijke Mededelingen, no 119.
Krebs, C.J., D. Reid, A. Kenney, D. Morris & S. Gilbert. 2008. Small mammal population moni-toring.
ArcticWOLVES sampling protocols, Université Laval, Québec (available online:
www.cen.ulaval.ca/arcticwolves/files/protocols/small_mammal_abundance.pdf)
Krebs, C.J. 2009. Ecology: the experimental analysis of distribution and abundance, 6th edition. Benja-
min Cumings, San Francisco, United-States, 655 pp.
Naughton, D. (2012) The natural history of Canadian mammals. University of Toronto Press, Toronto,
Canada, 824 pp.
Soininen, E. M., I. Jensvoll, S. T. Killengreen, and R. A. Ims. 2015. Under the snow: a new camera trap
opens the white box of subnivean ecology. Remote Sensing in Ecology and Conservation, doi:
10.1002/rse2.2 (early view).

55


Dicrostonyx groenlandicus
Dicrostonyx nunatakensis
Dicrostonyx richardsoni
Lemmus trimucronatus
Microtus longicaudus
Microtus miurus
Microtus oeconomus
Microtus pennsylvanicus
Microtus xanthognathus
Myodes gapperi
Myodes rutilus
Neotoma cinerea
Peromyscus keeni
Peromyscus maniculatus
Phenacomys intermedius
Synaptomys borealis
Zapus hudsonius
Northern collared lemming
Ogilvie mountains collared lemming
Richardson’s collared lemming
Brown lemming
Long-tailed vole
Singing vole
Tundra vole
Meadow vole
Taiga vole
Southern red-backed vole
Northern red-backed vole
Northern bushy-tailed rat
Northwestern deer mouse
Deer mouse
Heather vole
Northern bog lemming
Meadow jumping mouse

X
X
X
X
X
X
X
X
X
X
X
X
X
X
X

X
X
X
X
X
X
X
X
X
X
X
X
X
X
X

X
X
X
X
X
X
X
X
H
ere we present all the species present in the three Canadian territories (Naughton 2012):
Yukon (YU), Northwest territories (NWT), and Nunavut (NU). The northern collared
lemming and the brown lemming are the only two species present in the Canadian Arctic
Archipelago. Other species present in Nunavut may be found on the southern continental area
of the territory. The current work deals with methods for sampling small mammals in the Arctic
Archipelago only but similar techniques described here may be applicable elsewhere
considering the ecology of the other species present in the study area.
56
CADIEUX, M.-C., FAUTEUX, D., GAUTHIER. G. 2015
‒ VERSION 1. CENTRE D’ÉTUDES NORDIQUES, U
... Therefore, we suggest that identification keys should be used to identify skull parts to determine the species that each mandible found belongs to. In Appendix S1, we present an illustrated identification key to mandibles of Dicrostonyx, Lemmus, Microtus and Myodes based on characteristics used in the literature to differentiate them (Naughton, 2012;Cadieux, Fauteux & Gauthier, 2015). Relationship between body mass and mandible size often varied among locations, which suggests potential genetic differentiation or local environmental effects, or an interaction between both through epigenetics on body growth. ...
Article
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Predator–prey interactions can control population fluctuations of several terrestrial vertebrates and energy fluxes in food webs. Quantifying these interactions typically requires the number of prey consumed by predators to be known, but prey size is often ignored. We hypothesized that rodent mandibles, which are routinely found in predatory bird pellets and mammalian scats, could be used to accurately determine prey size and thus estimate biomass consumed by Arctic predators. We used 1863 lemmings and voles from museum and field specimens collected across the North American Arctic to relate three measurements of the dentary bone and one on the molar toothrow with individual body mass. When species and location of specimens are known, our results suggest that the body mass of small rodents can be estimated with high precision using the dentary bone measurements (average R2 ranging from 0.73 to 0.81), especially for lemmings and Microtus voles. Body mass can also be estimated with reasonable precision using the dentary bone measurements even when species or location was unknown (0.71 ≤ R2 ≤ 0.80). Equations to convert mandible size to body mass are provided for site‐ and species‐specific estimations. Geographic variations in the relationship between mandible size and body mass were found, suggesting potential effects of genetic isolation or interactions with the immediate environment on size. Using mandible measurements in prey remains allows more precise estimation of biomass consumed by predators, which is essential to quantify energy fluxes within ecosystems and examine resource partitioning among Arctic predators.
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Snow covers the ground over large parts of the world for a substantial portion of the year. Yet very few methods are available to quantify biotic variables below the snow, with most studies of subnivean ecological processes relying on comparisons of data before and after the snow cover season. We developed a camera trap prototype to quantify subnivean small mammal activity. The trap consists of a camera that is attached facing downward from the ceiling of a box, which is designed to function as a snow-free tunnel. We tested it by placing nine traps with passive infrared sensors in a subarctic habitat where snow cover lasted for about 6 months. The traps were functional for the whole winter , permitting continuous data collection of site-specific presence and temporal activity patterns of all three small mammal species present (the insectivorous common shrew, Sorex araneus, the herbivorous tundra vole, Microtus oecono-mus, and the carnivorous stoat, Mustela erminea) as well as abiotic conditions (presence/absence of snow cover and subnivean temperature). Based on their successful functioning (only 6% of the photographs appeared empty or were of poor quality, whereas ca 80% were of small mammals and the remaining of birds and invertebrates), we discuss how the new camera trap can enable sub-nivean studies of small mammal communities. This greatly increases the temporal resolution and extent of data collection and thereby provides unpreceded opportunities to understand population and food web dynamics in ecosystems with snow cover.
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We attempted to live trap lemmings under the snow in their preferred winter habitat at two sites in the Canadian Arctic using chimney-like boxes. Lemmings used the boxes during winter, but we had very low trapping success in April and May. During spring trapping, in contrast to most of the winter, subnivean temperatures became colder than ambient air temperatures. We hypothesize that our low success in spring resulted from lemmings' leaving the deeper snow areas where our boxes were located and moving to shallower snow or exposed tundra. We suggest that the trapping boxes could be successful if trapping occurred earlier during winter.
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A Northern Pocket Gopher can dig an amazing half a metre of tunnel through compacted clay soil in just 15 minutes. North American Beavers, along with humans, are the only mammals whose impact on their environment is so massive that it can be clearly seen with the naked eye from outer space. And there really are Narwhals - the single-tusked mammals that likely inspired the unicorn legend - living in the waters surrounding Greenland. Learning about any of these mammals on their own brings out fascinating traits and stories. But when considered alongside the entire mammal population of Canada - from the tiny Olive-Backed Pocket Mouse to the enormous Killer Whale, and the Arctic-dwelling Polar Bear to the more southerly Red Bat - a spectacular portrait emerges of the diversity and beauty of Canada’s animal life. The Natural History of Canadian Mammals is a beautifully illustrated, up-to-date guide to all 215 known species of mammals in Canada. It features brand-new, full-colour images of each species, as well as stunning photographs from Canadian Geographic magazine’s national photography competitions depicting the animals in their natural environments. Along with being a visual treat, this book is jam-packed with information accessible to readers at all levels. Detailed descriptions are provided of each mammal’s appearance, habitat, and behavior, while colour maps show their full distribution across Canada, North America, and globally. The book also includes practical guides on tracking and identification for readers who would like to learn how to spot mammals in the wild. Among its most special features is a series of colour plates with vignettes of the Canadian representatives of each group, sized relative to one another for easy comparison and linked to the full species accounts later in the book. Comprehensive and immensely valuable, The Natural History of Canadian Mammals will become a treasured companion for scientific researchers, animal lovers, and all those wishing to gain a greater appreciation of Canada’s natural wonders. The Canadian Museum of Nature, Canada’s national natural history museum, continues to author these wonderful books in its goal to inspire a greater understanding of the natural environment.
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Winter breeding under the snow is a critical ecological adaptation of lemmings and a key demographic process in their periodic multiannual fluctuations in abundance. However, logistic constraints limit our ability to quantify lemming winter reproduction. We evaluated a method to infer lemming reproduction based on the size distribution of feces found in their winter nests. We determined criteria allowing identification of reproduction from feces found in nests, using golden Syrian hamsters (Mesocricetus auratus) as a surrogate model. We found a large difference in individual mass of feces between juveniles at weaning and adults. Using bimodal distribution of feces size, mean size difference, and proportion of small feces, we showed that visual inspection of ≥30 feces was sufficient to infer hamster reproduction with an accuracy of >95%. We also applied the method to winter nests of collared lemmings (Dicrostonyx groenlandicus) and brown lemmings (Lemmus trimucronatus) found in the Canadian Arctic. Because characteristics of feces found in lemming winter nests matched those found in hamster nests, we suggest that the method can be used to detect winter reproductive activity of lemmings.
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Snow cover has dramatic effects on the structure and functioning of Arctic ecosystems in winter. In the tundra, the subnivean space is the primary habitat of wintering small mammals and may be critical for their survival and reproduction. We have investigated the effects of snow cover and habitat features on the distributions of collared lemming (Dicrostonyx groenlandicus) and brown lemming (Lemmus trimucronatus) winter nests, as well as on their probabilities of reproduction and predation by stoats (Mustela erminea) and arctic foxes (Vulpes lagopus). We sampled 193 lemming winter nests and measured habitat features at all of these nests and at random sites at two spatial scales. We also monitored overwinter ground temperature at a subsample of nest and random sites. Our results demonstrate that nests were primarily located in areas with high micro-topography heterogeneity, steep slopes, deep snow cover providing thermal protection (reduced daily temperature fluctuations) and a high abundance of mosses. The probability of reproduction increased in collared lemming nests at low elevation and in brown lemming nests with high availability of some graminoid species. The probability of predation by stoats was density dependent and was higher in nests used by collared lemmings. Snow cover did not affect the probability of predation of lemming nests by stoats, but deep snow cover limited predation attempts by arctic foxes. We conclude that snow cover plays a key role in the spatial structure of wintering lemming populations and potentially in their population dynamics in the Arctic.
Population research on terrestrial mammals in the Benelux
  • B Hoekstra
  • E Van Der Straeten
  • V Van Laar
Hoekstra, B., E. van der Straeten & V. van Laar. 1977. Population research on terrestrial mammals in the Benelux. Wetenschappelijke Mededelingen, no 119.
Small mammal population moni-toring. ArcticWOLVES sampling protocols
  • C J Krebs
  • D Reid
  • A Kenney
  • D Morris
  • S Gilbert
Krebs, C.J., D. Reid, A. Kenney, D. Morris & S. Gilbert. 2008. Small mammal population moni-toring. ArcticWOLVES sampling protocols, Université Laval, Québec (available online: www.cen.ulaval.ca/arcticwolves/files/protocols/small_mammal_abundance.pdf)
NWT Small Mammal Identification. GNWT
  • Enr
ENR. 2005a. NWT Small Mammal Identification. GNWT. 27 pp. Available at http://www.enr.gov.nt.ca/ sites/default/files/documents/small_mammal_identification.pdf