The 45 species of mammals at Mammoth Cave National Park vary widely, from the pygmy shrew (among one of the smallest mammals on earth by weight) to white-tailed deer, to North America’s only marsupial, the opossum. If you look carefully, you may see their tracks on the moist ground. But if you’re looking in the daytime, tracks may be all you see. Most of these creatures are far more active at night – especially the bats.
The only mammals that truly fly, bats have inhabited the lightless halls of Mammoth Cave for millions of years. Only 150 years ago, Indiana bats (Myotis sodalis) and to a lesser extent gray bats (Myotis grisescens) were prominent species in Mammoth Cave, but are today listed as endangered. Little brown bats (Myotis lucifugus) were also abundant with the big brown bat (Eptisecus fuscus), and eastern pipistrelle (Pipistrellus subflavus) being less common. All together, these and more rare bat species such as eastern small-footed bat had estimated populations of 9-12 million just in the Historic Section. While these species still exist in Mammoth Cave, their numbers are now no more than a few thousand at best. Ecological restoration of this portion of Mammoth Cave, and facilitating the return of bats, is an ongoing effort. Not all bat species here inhabit the Cave; the red bat (Lasiurus borealis) is a forest-dweller, found underground only rarely.
Other mammals common in Mammoth Cave National Park include bobcats, coyotes, foxes, muskrats, gray squirrels, flying squirrels, rabbits, raccoons, skunks, beaver, mink, weasels, groundhogs, chipmunks, moles, voles, mice, and woodrats. The park is also planning to reintroduce river otter to this part of the Green River in early 2007.