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Bruce Vento Small Mammal Survey

posted Sep 12, 2018, 6:50 AM by Jonathan Poppele   [ updated Sep 12, 2018, 7:08 AM ]
On Sunday, August 5, 11 members of the Minnesota Wildlife Tracking Project tagged along on a small mammal survey of the Bruce Vento Nature Sanctuary. They survey was led by Dakota Rowsey, a mammalogist from the Bell Museum of Natural History. We were invited by Mary Heneke-Haney of St. Paul Parks and Recreation, who has been organizing the surveys for the past several years.

Dakota and his assistant set out Sherman traps and tracking plates the night before. We collected sprung traps and handed them over to the researchers to open. Dakota would shake the critter out into a plastic bag to identify and record before releasing it. He also took measurements on a sample of the animals. As trackers, we rarely get to identify small mammals to species, and often see only sparse evidence of their presence. On this survey, we got to see three different species of tiny mammals up close and learn some identification tips from a pro.

deer mouse
As expected, the most common animals caught in the traps were deer mice (Peromyscus maniculatus). Members of this genus are very similar to one another, and probably cannot be identified to species by tracks or sign. In hand, however, the bi-colored tail distinguishes deer mice from white-footed mice (Peromyscus leucopus). Although there are likely other species of mouse in the park, only deer mice showed up in our traps. But we got to see a diverse representation of this common species including juveniles, a pregnant female, and a host of a botfly larva (a member of the genus Cuterebra).

The traps also captured a few meadow voles (Microtus pennsylvanicus). As feeding sign (and owl pellets) from Ft. Snelling have suggested to us, meadow voles are quite common in the metro area river valley. Southern Minnesota is home to both meadow voles and prairie voles (Microtus ochrogaster), with the meadow vole being more abundant and wide-spread. Dakota shared with us that, unlike most voles, prairie voles are monogamous. As a result, males have much smaller testes than the otherwise similar looking meadow vole who are, as we got to see, remarkably well endowed.

The last set of traps we opened revealed a masked shrew (Sorex cinereus). And a pregnant female at that. The name "masked shrew" is a bit misleading, as this tiny insect hunter is almost entirely uniform in color. Like many of the animals we saw that day, she came out of the trap wet from tip to tail. Dakota told us that these small mammals will often urinate on themselves when trapped to help keep cool as the temperature rises.

Besides the close look at a few resident mammals, our group also got a chance to play sleuth looking at a tracking plate. One of the plates that Dakota had set out was covered with prints that initially looked a bit like mushrooms. A close look revealed that they were the hindquarters of frogs. Typically frog tracks only show the claw marks from the hind feet and, sometimes, the front prints. Here, the frogs rump and thighs had picked up enough graphite to leave clear prints on the contact paper.

Our group had a wonderful time in the field seeing these little critters up close and, from all we heard, our hosts truly enjoyed getting out in the field and sharing with a group of curious nature geeks. We expect to make this an annual event and look forward to taking part next year.