ANN ARBOR—They’re not blind and there are definitely more than three of them. And they may be the bearers of clues to the future for plant and animal species. Phil Myers, associate professor of zoology at the University of Michigan, who has been studying mice populations for the past 15 years, says that two of these rodents that make their home in Michigan have been shifting their population distributions since the beginning of the century.

Using historical records, Myers found that in 1901-31 the woodland deer mouse (Peromuscus manicularus gracilis) was the common inhabitant of the northern part of Michigan’s lower peninsula. By the middle of the 20th century, records show a different picture. In 1931-61, the population distribution of woodland deer mice declined.

Woodland deer mice live in forests. The old-growth pines of Michigan were lumbered for profit or leveled for farming during the 19th century, diminishing the habitat available to the mice. These forests have recovered since then, and at the beginning of this century, woodland deer mice were found as far south as Lansing. In 1983, it was Clare County. Now, the farthest south that woodland deer mice are being found, according to Myers’ research, is Otsego County, Michigan’s second northernmost county.

A species that prefers the same living conditions as the woodland deer mouse is the white-footed mouse (Peromyscus leocupus). Myers’ research indicated that in the first half of the 20th century, the white-footed mouse wasn’t found north of Lansing or in the Upper Peninsula. Within the last five years, however, the white-footed mouse population has appeared throughout Michigan’s lower peninsula and in the western portion of the state’s Upper Peninsula.

Based on 10 years of “censusing” mice populations in northern Michigan, Myers noticed that the white-footed mice populations tend to decline after a hard winter. This leads researchers to believe that the most important difference between the woodland deer mouse and the white-footed mouse is the ability of the former to withstand cold winters.

Myers and Barbara Lundrigan, a faculty member in zoology at Michigan State University, submitted a joint proposal to the Michigan Department of Natural Resources to study these populations further. Using teams of people live-trapping specific areas, Myers and Lundrigan hope to document the change in mice population distributions.

The larger picture has yet to be discovered. But if these populations change due to variations in established weather patterns, then the behavior of the woodland deer mice may be indicative of a larger impact on plant and animal species by changing temperatures.