Monitoring
your
Wetland
a primer to site-level monitoring activities for volunteer coordinators
Small
Mammals
. . . . . . . . . .
W
hen you think of wetland wildlife,
you might think of creatures bearing
feathers, exoskeletons or clammy
skin, but many fur-bearing animals also make
their homes in wetlands. In fact,
many of Wisconsin’s most
abundant and diverse mammal
populations live in wetland areas.
Bountiful food resources allow
small mammals to thrive in and
along wetlands. And small mammals help wet­
lands flourish as they disperse seeds, provide
predators with food, aerate soils with burrows
and help control insect populations.
LOW
HIGH
RESOURCES
E X P E RT I S E
HIGH
LOW
“Small mammal” is a generic grouping
biologists generally use to refer to shrews, moles,
mice, voles, gophers and ground squirrels. Some
biologists also include weasels, tree squirrels,
rabbits and hares, as we have in the list of small
mammal species on page 6 of this publication.
Most biologists arbitrarily exclude bats, which
get special recognition because of the unique
methods involved in surveying them. “Small
mammals” should not be confused with “small
game” which is a formal term the Wisconsin
Department of Natural Resources uses to identify
a very specific list of bird and mammal species
that are subject to harvest regulations.
About Small Mammal Surveys
S
mall mammal surveys can raise awareness
conser­vation and management efforts are
among volunteers and better characterize
making progress. Small mammal species are
your wetland. Volunteers detecting and document­
not equally valuable in providing state biolo­gists
ing the presence or absence of small mammal
and site-level volunteer groups with useful infor­
species in a wetland develop an enhanced
mation. Generalist species, such as the Eastern
understanding of wetland ecology and produce
chipmunk, meadow vole and Eastern cottontail,
species inventories that expand what is known
are found in large numbers through­
about the wetland. And particu­larly well-docu­
out most of Wisconsin. These
mented small mammal surveys can help biologists
species are not affected by
better understand distributions, habitat associa­
tions and population statuses for various species
of small mammals throughout the state.
At the site level, small mammal
The ermine, also called
surveys can also help identify when a
short-tailed weasel
wetland is providing quality habitat or
Steve Hillebrand/USFWS
This publication is part of a Monitoring Your Wetland series available online in pdf format at:
wetlandmonitoring.uwex.edu
Monitoring Your Wetland – Small Mammals
About Small Mammal Surveys – continued from front page
an inventory that represents your wetland as
closely as possible.
Small mammals are difficult to detect
through casual observation. They don’t chirp in
the morning or croak at night, and those that fly
only emerge under the cover of darkness. Most
spend a great deal of time hiding underground
or in thick vegetation, and when they do come
out into the open they often wait for nightfall.
Consequently, trapping is the most common
method used to detect small mammal species.
To trap small mammals in your wetland, you will
need to apply for a DNR collection and research
permit. You can learn more about the permit
by visiting the DNR Web site and by contacting
your local DNR biologist (see Informational
Resources on back page).
”
WDNR photos
“
subtle variations in habitat. Their presence
indicates little about habitat quality and the
success of conservation and management
efforts.
Data on habitat specialists or species on
the edge of their habitat range is much more
useful. The detection of the prairie vole in a
Wisconsin wet­
To trap small mammals land that has
undergone
in your wetland, you
restoration, for
will need to apply for a
example, would
DNR collection and
be a significant
research permit.
marker of
success. This
habitat specialist is common in Illinois, but
rare in Wisconsin. When interpreting small
mammal survey data, remember that it can be
easy to draw misleading conclusions. Some­
times a small mammal survey will detect few
species even when the quality of the wetland
being surveyed is high. Many factors can
influence species detection, including natural
cycles in population abundance, poor surveying
methods and other factors which may have
little or nothing to do with the quality of the
wetland.
Monitoring small mammals is challenging
and requires DNR technical assistance. With
the help of DNR biologists, you can establish a
project design that will most effectively achieve
monitoring goals without adversely impacting
the wetland or the health of your volunteers.
This publication will provide an overview of small
mammal surveying methods to help you deter­
mine if small mammal moni­toring is the right
activity for your volunteer group. This overview
will outline small mammal survey methods that
can maximize species detection and produce
Museum Special, baited
Sherman Live Trap, baited
2
Monitoring Your Wetland – Small Mammals
Supplies and Equipment
Trapping requires a lot of special­
the rim is flush with the ground.
Rat traps are best for capturing
ized equipment, which can easily
The pitfall trap is most efficient at
ground squirrels, chipmunks and
add up to well over $1,000 for
capturing small species such as
weasels, while the mouse trap is
even a small monitoring project.
shrews and some voles. Pitfall
best for capturing mice, voles and
Fortunately, the DNR has a supply
traps can be cylindrical tin cans
shrews. The Museum Special trap
of equipment available to lend
or plastic buckets, but the plastic
is designed to avoid damaging an
to volunteer groups, including
conical design favored by the
animal’s skull, which is important
weigh scales and an assortment
DNR is easier to maintain, store
for identification.
of traps.
and transport.
To capture the greatest range of
To make the pitfall traps more
species, volunteers surveying with
effective, volunteers should
traps should use a combination
either place them near fallen logs
of three basic types – live box traps
or construct a drift fence, a short
(e.g., Sherman box traps), pitfall
barrier made of ridged plastic or
traps and snap traps. Although
metal flashing that directs animals
these three are the basic traps you
toward the trap. Small mammals
need to capture a wide variety of
crawl along the barrier looking
animals, you might use additional
for an opening and then fall into
traps to emphasize the capture
the trap.
of particular species.
Sherman Box Traps
The Sherman box trap is a live trap
made of aluminum or galvanized
steel that comes in a wide variety
of sizes. The large trap, measuring
3 x 3.5 x 9", is most common. It is
good for capturing voles, mice and
some shrew species. When a small
animal steps on a treadle inside
the trap, a latch holding back a
compressed spring is released and
the trap’s door snaps shut. Some
Sherman traps fold up for storage
and transport, handy when volun­
teers need to carry tens or even
hundreds of traps to a site.
Pitfall Traps
A pitfall trap consists of an opentopped container buried so that
Bait
When using the Sherman and
snap traps, and occasionally
pitfall traps, volunteers will need
to lure animals with bait. The most
commonly used bait is a mixture
of peanut butter and oatmeal or
birdseed. Apples, potatoes, grapes
or other firm vegetables and
fruits can also be used as bait or
as sources of moisture for captive
Precautions should be taken to
animals. Although peanut butter
ensure pitfall traps do not become
works well, some monitoring
lethal. When heavy rain is expected,
groups also use higher quality
for example, volunteers should
baits such as walnuts, pieces of
reschedule the survey. Small mam­
earth­worm or insect larvae, to
mals can easily drown or die of
help lure insectivores, particularly
hypothermia in a pitfall trap filled
shrews. Larvae should be freezer
with water. A small piece of hard
killed to prevent them from crawl­
foam placed in each trap increases
ing out of the trap.
the likelihood that a small mammal
will survive if unexpected rain
Scales
should occur. Volunteers also
To make accurate weight
should place a rain and sun shield
over the trap.
measure­ments in the field,
volunteers will need
portable spring scales. The
Snap Traps
type of scale needed will
Three types of snap traps are
depend on the species
commonly used to lethally capture
being weighed. Using the smallest
small mammals – a standard retail
scale possible for the animals
rat trap, a standard retail mouse
being weighed results in more
trap and, occasionally, the profes­
accurate measurements.
sional-grade Museum Special.
3
Monitoring Your Wetland – Small Mammals
Survey Participants
A
survey team needs a highly skilled leader
to guide volunteers, ensure traps are
properly set, assist with species identification
and manage data. Volunteers can get by with
moderate skills. Additionally, you will want
volunteers who can commit to several days or
even several seasons of survey work. Trapping
and identifying mammals requires training and
the less volunteer turnover you have the more
likely your volunteers are to collect representative
data. Improperly set traps catch few mammals
or only the most common mammals. Also,
surveys result in more representative
inventories when data is collected over several
years rather than a single season, which will
be easier to achieve with volunteers that return
for multiple surveys. The overall number of
volunteers you require will depend on the size
of your wetland. Generally teams of two to
three people works best, but larger groups can
be deployed if enough equipment and team
leaders are available.
Surveying – When, Where & How
T
he most important small mammal
surveys will use live traps whenever possible,
survey­ing months are July, August and
however, these traps are significantly more
September. To get a complete collection of
expensive, take more time to tend and require
species, conduct at least some surveying
more maintenance. They also are a poor choice
before the end of August.
for trapping in the fall, when
Some small mammals, such as
trapped mammals can quickly
Checking traps,
Franklin’s ground squirrels,
become hypothermic and die.
identification,
animal
thirteen-line ground squirrels
Checking traps, identifica­
processing
and
data
and jumping mice, can begin
tion, animal processing and data
collection
are
time
hibernating as early as Septem­­
collection are time con­suming,
con­suming, and
ber. Ideally, two to three surveys
and volunteer groups must be
should be conducted in a
careful not to set more traps
volunteer groups
season to obtain representative
than they can manage. If just one
must be careful not to
inventory data.
volunteer is conducting a survey,
set more traps than
Normally, traps are set in
they should not use more than
they can manage.
the evening and checked within
100 traps at one time. If two vol­
a few hours of sunrise to coin­
unteers are conducting a survey,
cide with the peak hours of small mammal activity
they may be able to set 150-200 traps. Pit­fall
and to avoid trap mortality during the heat of
traps are the most labor intensive to install. But
the day. Surveys should be rescheduled when
because pitfall traps help surveyors capture a
there is inclement weather. Poor weather
greater diversity of mammal species, most surveys
conditions can change small mammal behavior,
include one for every ten traps set.
lower trapping success rates and increase the
Proper trap placement is key to efficiently
likelihood that live-captured animals will die while
capturing mammal species. Traps should not be
waiting to be released. Most small mammal
set randomly throughout the habitat, but along
“
”
4
L. Ayers, WDNR
Monitoring Your Wetland – Small Mammals
Small mammal field work.
a trap line. A trap line is an imaginary line of a
designated length running through the habitat,
along which the traps are placed. Traps are not
set directly on the trap line, but should be
within two meters of a designated point along
the trap line. Each trap should be located approx­
imately 10 to 20 meters from the previous trap.
Additionally, Sherman and snap traps should
be placed close to the ground and near cover
rather than in the open. Good locations might
include areas under bushes or alongside
woody debris and rocks. Volunteers should
mark traps with small flags or brightly colored
tape, and use a wetland map or global
positioning system (GPS) unit to document
trap locations.
Surveying – Health Considerations
T
o reduce fatality among live-trapped animals,
volunteers need to minimize stress. Traps
should be checked as soon as possible to min­
imize the time the animal is confined. To ensure
captured mammals do not become hypothermic
or starve, volunteers should provide extra food
and nesting mater­ials. Wads of cotton or wool
can help small mammals stay warm until traps
are checked. Moist foods such as carrots can
help prevent captured animals from becoming
dehydrated.
Generally, live traps should not be set
during the day in June through mid-September,
unless you can check traps every two to four
hours, otherwise trapped animals can become
overheated and die. Additionally, data collected
with daytime trapping has not been found to
notably improve survey results otherwise
based on nocturnal trapping. Traps set in the
evening and during the day should be situated
where they will be shaded. Finally, volunteers
should handle the animals as little as possible
when examining them.
Volunteers handling small mammals
also need to be trained to use safe handling
methods to protect themselves from bites and
transmissible diseases. DNR biologists providing
volunteer coordinators with technical advice
can also provide instruction on safe handling
procedures.
5
Monitoring Your Wetland – Small Mammals
Identification
I
guess. If a volunteer identifies a deer mouse, but
without determining whether it is a woodland
or prairie deer mouse, they should not report
anything further than that it is a deer mouse.
Subspecies distinctions are important.
Identification
of some small mam­
WISCONSIN SPECIES
COMMONLY
mal species such as
CATEGORIZED AS
the pygmy shrew,
“SMALL MAMMALS”
masked shrew and
Arctic shrew
prairie vole, need to
Masked shrew
be verified with a
Pygmy shrew
Water shrew
close examination of
Northern short-tailed shrew
their teeth. Conse­
Eastern mole
quently, they must
Star-nosed mole
be killed in order to
Plains pocket gopher
obtain a proper
Least chipmunk
Eastern
chipmunk
identification.
L. Ayers, WDNR
dentifying small mammals can be challenging.
Some species are very similar in appearance
and size, and are difficult to distinguish. This is
particularly true among some of the smallest
species. To avoid misidentifications, coordinators
should instruct volunteers to use a checklist of
minimum standards for properly identifying a
particular species of mammal. When using the
checklist, volunteers should document the
observations they used to make the identification
such as measurements and features unique to
the species identified.
Flow charts providing a checklist of
identification indicators can be obtained from
the DNR. In order to make a proper identification
volunteers must follow the hierarchy indicated
in the flow chart. A volunteer who cannot make
a complete identification should not attempt to
Franklin’s ground squirrel
Thirteen-lined ground
squirrel
Woodchuck
Northern flying squirrel
Southern flying squirrel
Red squirrel
Grey squirrel
Fox squirrel
Western harvest mouse
White-footed mouse
Deer mouse
Southern red-backed vole
Prairie vole
Meadow vole
Woodland vole
Southern bog lemming
Woodland jumping mouse
Meadow jumping mouse
Ermine
Long-tailed weasel
Least weasel
Cottontail
Snowshoe hare
Muskrat
Masked shrew
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Monitoring Your Wetland – Small Mammals
SMALL MAMMALS
Woodchuck
Woodchuck & Muskrat: Jeffrey J. Strobel; Meadow Vole: Joe Kosack, Pennsylvania Game Commission; Meadow jumping mouse: USFWS
Muskrat
Meadow Vole
Meadow jumping mouse
Data Collection & Record Keeping
W
hen documenting data, volunteers
should record as much information
about a captured mammal as possible, including
its weight, size, species, age, sex and where it
was captured. To determine the sex of a small
mammal volunteers need to examine its
genitalia. Determining sex for especially small
species like shrews and immature animals can
be difficult, but can be learned with the technical
assistance of DNR biologists.
Data entry for small mammals is less
developed than for many other taxonomic
groups and, for the most part, still relies on
paper records. Volunteers send their annual
small mammal reports and forms to a DNR
small mammal expert. If a volunteer group
does a good job of documenting their effort
and methods, the data can be used to help
complete distribution maps of species, even if
no unusual or rare species were found. It is just
as important to know where species are not
being found as it is to know where they are
being found.
To submit data to the DNR, volunteer
groups should contact the DNR’s Citizen-Based
Monitoring Program coordinator or the mammal
ecologist. See Information Resources on the
back page for current contact information.
7
Monitoring
your
Wetland
a primer to site-level monitoring activities for volunteer coordinators
The Monitoring Your Wetland
series includes 9 sections:
Small Mammals
•Introduction to Wetland
Monitoring
. . . . . . . . . . . . . . . . . . . . . . . . . . .
Small Mammals
INFORMATIONAL RESOURCES
Resources Inventory Committee of British Columbia Biodiversity
Inventory Methods Series
This inventory series includes a detailed manual on methods for monitoring small
mammals. Although the protocols are not specific to Wisconsin or wetlands, they are
for the most part broadly applicable and should be easily adapted for use in
Wisconsin wetlands.
http://archive.ilmb.gov.bc.ca/risc/pubs/tebiodiv/smallmammals
Wisconsin Department of Natural Resources Magazine, Small for One and
One for Small
•Birds
• Dragonflies & Damselflies
(Odonata)
•Frogs and Toads (Anurans)
• Butterflies (Lepidoptera)
• Invasive Plants
• Water Quality
• Macroinvertebrates
Available online in pdf format at:
wetlandmonitoring.uwex.edu
This article provides an easy to understand overview of small mammal
surveying methods.
http://dnr.wi.gov/wnrmag/html/stories/2006/apr06/small.htm
Wisconsin Department of Natural Resources Citizen-Based Monitoring Program Coordinator
Volunteer coordinators who choose to begin a small mammal monitoring project should contact the DNR’s current
Citizen-Based Monitoring Program coordinator for assistance with project design, technical information, to borrow
DNR trapping equipment and to obtain identification flow charts. The current coordinator is Loren Ayers, who can
be reached at (608) 261-6449 or [email protected]
Kurta, A. 1995. Mammals of the Great Lakes Region.
University of Michigan Press, Ann Arbor, MI. 376pp.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
March 2011
Project coordination by the Rock River Coalition and Suzanne Wade, UW-Extension Basin Education Initiative.
Researched and written by Patrice Kohl
With editorial contributions from Loren Ayers, Wisconsin Department of Natural Resources terrestrial ecologist. Editorial
assistance by Marie Martinelle and graphic design by Jeffrey J. Strobel, UW-Extension Environmental Resources Center.
Photography by Jeffrey J. Strobel except where otherwise noted.
Project funded through a DNR Citizen-Based Monitoring Partnership Program Grant with support from University of Wisconsin-Extension.
University of Wisconsin, U.S. Department of Agriculture and Wisconsin counties cooperating. An EEO/AA employer, University of Wisconsin Extension
provides equal opportunities in employment and programming, including Title IX and American with Disabilities (ADA) requirements.