Rodents are the most numerous mammals in Rocky Mountain National Park in terms of numbers of individuals, and this Order contains one third of the species of known living mammals. The Rocky Mountain National Park species list for mammals includes 23 species of rodents, in six families. The Castoridae (beavers), Geomyidae (pocket gophers), Dipodidae (jumping mice), and Erethizontidae (New World porcupines) each have only one representative in the park. However, there are nine species of Sciuridae (squirrels) and ten species of Muridae (the native rats and mice) known from the park.
While the park's rodents live in a wide diversity of habitats - from ponds to tundra, eat a wide range of vegetable matter or carrion, and can weigh less than the change in your pocket (adult deer mice and western jumping mice weigh about 20 grams or the weight of about four nickels) to over 40 pounds (beaver), they all have one common characteristic - their teeth. Rodents' teeth are specialized for gnawing. Their incisors (front teeth) continue to grow throughout their lives. The fronts of the teeth are covered with enamel, but the backs are not. As rodents gnaw, they wear the backs of their teeth away, keeping the fronts of the teeth at a sharp chisel point, and making them even more effective at gnawing.
The park's rodents are viewed by humans in both positive and negative ways. One study showed 19% of the park's deer mouse population carried hantavirus, and park rodents are also known to carry plague. A few simple precautions, including following rules about not feeding wildlife, can prevent visitors from contracting these diseases. However, rodents play an important role in maintaining the park's naturally functioning ecosystems, as well. Beavers play an important role in creating and maintaining wetlands. Rodents are also an important source of food for birds of prey such as hawks and owls, and for most of the park's carnivores including coyotes, fox, bobcats, and weasels. Rodents also provide some of the park's most cherished viewing and photo opportunities for visitors, with ground squirrels, tree squirrels, and beavers being among the most popular animals.