"The Prairie Vole builds well-defined runways on and below ground. Surface runways are often well worn and bare of vegetation; sometimes they are covered with a layer of grass clippings. The abundance of these runways is a good index of the size of the Vole's local population. Unlike most voles, and in fact, most mammals, Prairie Voles appear to be monogamous: male-female breeding pairs stay together. Offspring are born hairless yet develop rapidly, acquiring a brown furry coat by day two, crawling three days later, and eating solid food by day 12. They are weaned at 2-3 weeks, and fully grown by two months."

Links:
Mammal Species of the World
Click here for The American Society of Mammalogists species account