Woodrats – familiarly known as "pack rats" – are beautiful and interesting animals that hardly deserve the negative stereotype most people have of "rats." Desert woodrats (12 inches long, 4 ½ ounces) are the smallest of Coloradan species; the bushy-tailed woodrat of mountain talus slides and mining camps (to over 16 inches long and 11 ounces) is the largest. These are fastidious, beautiful animals. Color differs from gray (gray woodrat) to blackish brown (Mexican woodrat), to rich reddish tan (bushy-tailed woodrat), and most have white to grayish bellies.
Woodrats are known as pack rats because they pick up any curious object they find in their habitat and "pack" it home to the den, where bits of rock or wood, cow chips, bones and hardware all add to the strength of the house. A peculiar characteristic is that if woodrats find something they want, they will drop what they are currently carrying, for example a piece of cactus, and "trade" it for the new item. They are particularly fond of shiny objects, leading to tales of rats swapping jewelry for a stone or cow chip.
Range: Most parts of Colorado have one or another of the state's six woodrat species. The eastern woodrat lives in riparian woodlands on the eastern plains, and the gray woodrat occurs in southeastern Colorado.
Habitat: Woodrats prefer the rough, broken terrain of canyon and mesa walls of the Colorado Plateau; building dens in holes around cholla cactus, the cactus’ spines act as protection against predators.
Many generations of woodrats may use a choice den site, adding over decased to the house, latrine, and a sticky accumulation of urine. The urine catches pollen and other debris blown from the surrounding area and thus captures a sample of the environment of a particular time. Dated by carbon-14, fossil woodrat middens, or manure piles, have provided information to reconstruct changing habitats of the Southwest over the past 40,000 years.
Reproduction: Inside the house is a grass-lined nest where the animals spend cold weather and rear young. Females produce up to four litters of one to six young after a gestation period of four to five weeks. Woodrats are fairly protected in their dens, but still owls and coyotes take a toll as do gopher snakes and rattlesnakes. Adults may live several years.
By David M. Armstrong
Department of Ecology & Evolutionary Biology
Environmental Studies Program, University Museum of Natural History
University of Colorado-Bouldermausmann@aol.com