Procedures - Rare animal surveys: Small mammals

Little brown bat.
Biologists survey caves during winter months to find hibernating bats such as this Little brown bat (Myotis lucifigus).

Photo by G. Nordquist.

The Minnesota Biological Survey (MBS) conducts mammal surveys for small-to-medium sized mammals. DNR Wildlife Research biologists and managers conduct surveys of large mammals, using techniques that differ greatly from those used by MBS. Field surveys of small, terrestrial mammals, such as shrews, voles and mice, are conducted from July through August when population levels are high. Surveys for bats are conducted during the summer and winter. Survey techniques include the following:

Small mammal trap grids use a variety of traps that are set in a grid array. The traps are checked regularly, all animals captured are identified and measured. Live animals are marked with permanent markers and released.

Cage traps are set for larger mammals, such as the eastern spotted skunk.

Bat surveys during summer involve documenting foraging bats and locating maternity colonies. Using a bat detector and laptop computer, the ultrasonic calls of foraging bats are displayed on the computer screen and permanently stored in electronic files. Old buildings and hollow trees are searched for maternity colonies (aggregations of female bats that group together to give birth and raise their young). During the winter, caves and mines are searched for hibernating bats.

mammal sampling photo
MCBS mammalogist Gerda Nordquist (far right) instructs mammal crew staff on proper sampling techniques.

Photo by C. D. Hall.

Other observations, such as road-killed mammals, tracks, dens, and vocalizations, are recorded when encountered.