I believe that these are Meadow Voles, Microtus pennsylvanicus; I've sent them to Dr. John Whitaker at Indiana State University for a positive identification. You may be thinking... "looks like a mouse to me." Voles differ from mice in having rounder heads, smaller ears and eyes, stouter bodies, and shorter, hairy tails.
Meadow Voles are widespread in North America, found in a variety of habitats in all regions except the southwest and southcentral states. Research shows that their populations are secure, and that they actually seem to be expanding southward. Meadow Voles breed throughout the year, including in the winter if there is enough snow to act as insulation. They are active both during the day and at night. The life span of a Meadow Vole in the wild is up to a year, but is usually less.
Female Meadow Voles are said to be territorial, while the males have ranges that cover three times the area of a female. Unlike the males of other vole species (such as the Prairie Vole, Microtus ochrogaster), male Meadow Voles are promiscuous little guys. To be protected while they forage, these proficient diggers, create tunnels through vegetation and the ground beneath.
Look at those chompers! The diet of the Meadow Vole is comprised mostly of vegetation, though they have been known also to be cannibalistic. They must spend a good part of the day and night eating, as they are known to consume 60% of their body weight every day!
It is unfortunate that we continue to find these animals dead on our property, but doing so gives me a reason to learn more about the species. Even land as degraded as our old field is full of interesting creatures.