Little Mice on the Prairie...but no Voles
Friends of the Blufflands (FBL) recently teamed up with The Coulee Region Chapter (CRC) of The Prairie Enthusiasts in the La Crosse area to do a survey of small mammals living on Holland Sand Prairie (HSP). HSP is a 61-acre rare sand prairie located in La Crosse County that is a State Natural Area owned by the town of Holland, protected by a conservation easement by the Mississippi Valley Conservancy, and managed, in part, by the CRC. FBL participates in various activities on HSP. We were most interested in learning if the prairie vole, Microtus ochrogaster, a species of Special Concern in Wisconsin, was living on the prairie.
A meadow vole found at a different location
Voles are distinguished from mice by their smaller eyes and ears, short tails, stockier bodies, and a more rounded, blunted nose. There are four species of voles in Wisconsin. The most common, by far, is the meadow vole (M. pennsylvanicus). The prairie vole is much less common and is most often found on dry and sandy remnant native prairies or barrens. It is most reliably distinguished from the meadow vole by the number of bumps or tubercles on the bottom of the feet. Prairie voles have 5 tubercles, meadow voles 6.
Tubercles on the bottom of a foot of a meadow vole- 6 vs 5 for the prairie vole
The woodland vole (M. pinetorum), a rare vole found in forests and orchards, and the red backed vole (Clethrionomys gapperi), also somewhat uncommon and found in mixed conifer-hardwood forests of northern Wisconsin, make up the remaining two vole species. In 2021 Rich Staffen, conservation biologist of the DNR, reported prairie voles inhabiting new locations on some of the remnant native prairies in southwestern Wisconsin. The CRC and FBL contacted Rich in December 2021 about surveying HSP for the prairie vole. He was enthusiastic and agreed to provide expert help to get us started. He recommended doing the survey in late August or early September when these critters are at peak numbers.
Also of interest was which mice were living on HSP. The prairie deer mouse (Peromyscus maniculatus bairdii), also a species of Special Concern, and the western harvest mouse (Reithrodontomys megalotis) an uncommon species, were of particular interest.
On 8/30/22 Rich met us on HSP and discussed how to do the survey and provided information about how to identify the different voles and mice that could be caught. He also provided 50 small Sherman live traps. These were placed every 10 meters along a 500 meter transect, baited with peanut butter and oats, and left open for the night. The next morning Rich returned and met with a group from CRC and FBL to help us learn how to remove the mammals from the cages, do the measurements that are needed for identification, and then release them unharmed. After that, Rich left and we were on our own. The next three nights and mornings we repeated this process, opening and baiting the traps at about 5:00 pm, returning the next morning to check each trap, then closing it for the day.
Here are the results of our survey:
Day 1: 7 Prairie deer mice
Day 2: 12 Prairie deer mice, 1 western harvest mouse, 1 meadow jumping mouse (Zapus hudsonius)
Day 3: 17 Prairie deer mice
Day 4: 17 Prairie deer mice, 1 western harvest mice, 1 white footed mouse (Peromyscus leuopus)
The prairie deer mouse (PDM) and western harvest mouse (WHM) were difficult to tell apart short of examining the teeth, with the teeth being grooved in the WHM and without grooves in the PDM. We found for us, at our level of training, that the size, bicolored vs not bicolored tail, and belly or other fur color were not reliable distinguishing factors. We did not look at the teeth of every mouse until the last day, so some of the ones classified as PDM, especially on day 3, could have been WHM. The one WHM on day 2 was identified retrospectively with a review of photos of the teeth that were taken from some of the mice.
First day placing the traps along a transect with Rich Staffen holding the box
Weighing a mouse
Measuring the tail
Similar measurements were taken of the total body length, hindfoot, and ear.
The teeth proved to be the best distinguishing factor to tell a PDM from a WHM:
The teeth of the PDM without grooves
Grooved teeth of the WHM
A happy mouse being released after being measured
We were somewhat disappointed not to find voles on HSP, especially the prairie vole. Perhaps a survey done on a different transect of the prairie would find voles or other mice.
Overall this was a fun and interesting activity. The CRC and FBL plan to do similar surveys on other remnant prairies next year. Maybe the elusive prairie vole will show up in 2023!
Note that this article was previously published in the Prairie Promoter Fall 2022 issue