- Photo: Bill Kaufman
Pack rat nests may be occupied for centuries. These middens provide information about climate and vegetation changes.
Pack rats are solitary, nocturnal rodents. They are active year round, and are found throughout southwestern USA and Mexico. The body is 7 to 8 inches long, grayish brown on the back and lighter colored on the underside.
They are called pack rats because they collect pieces of cholla and prickly pear, twigs, scat from dogs, coyotes, and other animals, as well as paper, fabric, styrofoam and anything else they find. They especially like shiny objects. They use these items to construct their homes under prickly pears or other plants, or among boulders. The nest may have several chambers underground and extend several feet in each dimension above ground. Nests have multiple exits. The debris helps to insulate the nest, moderating the temperature and increasing humidity, and keeps out predators, such as coyotes, foxes, bobcats, and owls. Snakes often get into the nest. Kissing bugs also inhabit these nests and feed on the blood of the pack rats. Kissing bugs are not fatal to the pack rats, but in tropical climates they transmit Chagas Disease. Only one adult pack rat inhabits each nest.
Pack rat nests may be occupied for centuries. Fossil middens over 50,000 years old have been discovered, containing vegetation, pollen, bones, and reptile scales, encased in crystallized urine called amberat. These middens provide information about climate and vegetation changes.
Pack rats are primarily herbivores. They prefer prickly pear but will also eat grasses, and buds, seeds, and fruits of various plants. Less than 1% of their diet is animal material, usually insects. They don’t need to drink water. They get water from the succulent plants they eat.
The breeding season, gestation period, and time to reach maturity vary with location. They may have a couple of small litters a year. The mating system is polygynous. The life span is 4 to 6 years.