a primer to site-level monitoring activities for volunteer coordinators

This publication is part of a Monitoring Your Wetland series available online in pdf format at:wetlandmonitoring.uwex.edu

yourMonitoring

Wetland

About Small Mammal Surveys

Small mammal surveys can raise awareness among volunteers and better characterize

your wetland. Volunteers detecting and document­ing the presence or absence of small mammal species in a wetland develop an enhanced understanding of wetland ecology and produce species inventories that expand what is known about the wetland. And particu larly well­docu­mented small mammal surveys can help biologists better understand distributions, habitat associa­tions and population statuses for various species of small mammals throughout the state.

At the site level, small mammal surveys can also help identify when a wetland is providing quality habitat or

conser vation and management efforts are making progress. Small mammal species are not equally valuable in providing state biolo gists and site­level volunteer groups with useful infor­mation. Generalist species, such as the Eastern chipmunk, meadow vole and Eastern cottontail,

are found in large numbers through­out most of Wisconsin. These species are not affected by

. . . . . . . . . .Small Mammals

When you think of wetland wildlife, you might think of creatures bearing feathers, exoskeletons or clammy

skin, but many fur­bearing 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 wet­lands flourish as they disperse seeds, provide predators with food, aerate soils with burrows and help control insect populations.

“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.

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Steve Hillebrand/USFWS

The ermine, also called short-tailed weasel

About Small Mammal Surveys – continued from front page 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 wet­land that has undergone restoration, for example, would be a significant 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. Some­times 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 deter­mine if small mammal moni toring is the right activity for your volunteer group. This overview will outline small mammal survey methods that can maximize species detection and produce

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).

To trap small mammals in your wetland, you will need to apply for a DNR collection and research permit.”

“

Museum Special, baited

Sherman Live Trap, baited

WD

NR

phot

os

Monitoring Your Wetland – Small Mammals

2

Trapping requires a lot of special­

ized equipment, which can easily

add up to well over $1,000 for

even a small monitoring project.

Fortunately, the DNR has a supply

of equipment available to lend

to volunteer groups, including

weigh scales and an assortment

of traps.

To capture the greatest range of

species, volunteers surveying with

traps should use a combination

of three basic types – live box traps

(e.g., Sherman box traps), pitfall

traps and snap traps. Although

these three are the basic traps you

need to capture a wide variety of

animals, you might use additional

traps to emphasize the capture

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 open­

topped container buried so that

the rim is flush with the ground.

The pitfall trap is most efficient at

capturing small species such as

shrews and some voles. Pitfall

traps can be cylindrical tin cans

or plastic buckets, but the plastic

conical design favored by the

DNR is easier to maintain, store

and transport.

To make the pitfall traps more

effective, volunteers should

either place them near fallen logs

or construct a drift fence, a short

barrier made of ridged plastic or

metal flashing that directs animals

toward the trap. Small mammals

crawl along the barrier looking

for an opening and then fall into

the trap.

Precautions should be taken to

ensure pitfall traps do not become

lethal. When heavy rain is expected,

for example, volunteers should

reschedule the survey. Small mam­

mals can easily drown or die of

hypothermia in a pitfall trap filled

with water. A small piece of hard

foam placed in each trap increases

the likelihood that a small mammal

will survive if unexpected rain

should occur. Volunteers also

should place a rain and sun shield

over the trap.

Snap Traps

Three types of snap traps are

commonly used to lethally capture

small mammals – a standard retail

rat trap, a standard retail mouse

trap and, occasionally, the profes­

sional­grade Museum Special.

Rat traps are best for capturing

ground squirrels, chipmunks and

weasels, while the mouse trap is

best for capturing mice, voles and

shrews. The Museum Special trap

is designed to avoid damaging an

animal’s skull, which is important

for identification.

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

animals. Although peanut butter

works well, some monitoring

groups also use higher quality

baits such as walnuts, pieces of

earth worm or insect larvae, to

help lure insectivores, particularly

shrews. Larvae should be freezer

killed to prevent them from crawl­

ing out of the trap.

Scales

To make accurate weight

measure ments in the field,

volunteers will need

portable spring scales. The

type of scale needed will

depend on the species

being weighed. Using the smallest

scale possible for the animals

being weighed results in more

accurate measurements.

Supplies and Equipment

Monitoring Your Wetland – Small Mammals

3

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

The most important small mammal survey ing months are July, August and

September. To get a complete collection of species, conduct at least some surveying before the end of August. Some small mammals, such as Franklin’s ground squirrels, thirteen­line ground squirrels and jumping mice, can begin hibernating as early as Septem ­ber. Ideally, two to three surveys should be conducted in a season to obtain representative inventory data.

Normally, traps are set in the evening and checked within a few hours of sunrise to coin­cide with the peak hours of small mammal activity and to avoid trap mortality during the heat of the day. Surveys should be rescheduled when there is inclement weather. Poor weather conditions can change small mammal behavior, lower trapping success rates and increase the likelihood that live­captured animals will die while waiting to be released. Most small mammal

Survey Participants

Surveying – When, Where & How

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.

surveys will use live traps whenever possible, however, these traps are significantly more expensive, take more time to tend and require more maintenance. They also are a poor choice

for trapping in the fall, when trapped mammals can quickly become hypothermic and die.

Checking traps, identifica­tion, animal processing and data collection are time con suming, and volunteer groups must be careful not to set more traps than they can manage. If just one volunteer is conducting a survey, they should not use more than 100 traps at one time. If two vol­unteers are conducting a survey,

they may be able to set 150­200 traps. Pit fall traps are the most labor intensive to install. But because pitfall traps help surveyors capture a greater diversity of mammal species, most surveys include one for every ten traps set.

Proper trap placement is key to efficiently capturing mammal species. Traps should not be set randomly throughout the habitat, but along

Checking traps, identification, animal processing and data collection are time con suming, and volunteer groups must be careful not to set more traps than they can manage. ”

“

Monitoring Your Wetland – Small Mammals

4

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 approx­imately 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.

To reduce fatality among live­trapped animals, volunteers need to minimize stress. Traps

should be checked as soon as possible to min­imize the time the animal is confined. To ensure captured mammals do not become hypothermic or starve, volunteers should provide extra food and nesting mater ials. 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 mid­September, unless you can check traps every two to four hours, otherwise trapped animals can become

Surveying – Health Considerations 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.

Small mammal field work.

L. A

yers

, WD

NR

Monitoring Your Wetland – Small Mammals

5

Identifying 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

Identification 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 mam­mal species such as the pygmy shrew, masked shrew and prairie vole, need to be verified with a close examination of their teeth. Conse­quently, they must be killed in order to obtain a proper identification.

WISCONSIN SPECIES COMMONLY

CATEGORIZED AS “SMALL MAMMALS”

Arctic shrew

Masked shrew

Pygmy shrew

Water shrew

Northern short-tailed shrew

Eastern mole

Star-nosed mole

Plains pocket gopher

Least chipmunk

Eastern chipmunk

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

MuskratMasked shrew

L. A

yers

, WD

NR

Monitoring Your Wetland – Small Mammals

6

Woodchuck

SMALL MAMMALS

Muskrat Meadow Vole Meadow jumping mouse

When 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

Data Collection & Record Keeping 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 Citizen­Based Monitoring Program coordinator or the mammal ecologist. See Information Resources on the back page for current contact information.

Woodchuck & Muskrat: Jeffrey J. Strobel; Meadow Vole: Joe Kosack, Pennsylvania Game Commission; Meadow jumping mouse: USFWS

Monitoring Your Wetland – Small Mammals

7

INFORMATIONAL RESOURCES

Resources Inventory Committee of British Columbia Biodiversity Inventory Methods SeriesThis 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 SmallThis 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 Citizen­Based 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) 261­6449 or loren.ayers@dnr.state.wi.us

Kurta, A. 1995. Mammals of the Great Lakes Region. University of Michigan Press, Ann Arbor, MI. 376pp.

a primer to site-level monitoring activities for volunteer coordinatorsyourMonitoring

WetlandThe Monitoring Your Wetland series includes 9 sections:

•IntroductiontoWetland Monitoring

•Birds

Small Mammals

•Dragonflies&Damselflies (Odonata)

•FrogsandToads(Anurans)

•Butterflies(Lepidoptera)

•InvasivePlants

•WaterQuality

•Macroinvertebrates

Available online in pdf format at:

wetlandmonitoring.uwex.edu

. . . . . . . . . . . . . . . . . . . . . . . . . . .Small Mammals

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .March 2011

Project coordination by the Rock River Coalition and Suzanne Wade, UW­Extension 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, UW­Extension Environmental Resources Center. Photography by Jeffrey J. Strobel except where otherwise noted.

Project funded through a DNR Citizen­Based Monitoring Partnership Program Grant with support from University of Wisconsin­Extension.

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.