Arizona-Sonora Desert Museum Digital Library

Distinguishing Features

Rats are larger than mice. The white-throated woodrat (perhaps better known as packrat) is medium-sized (up to 1 pound; .45 kg), with big ears and eyes and a short tail. Hairs on this animal's throat are white to the bases.

Habitat

The white-throated woodrat is found throughout most of Arizona and Sonora in a variety of habitats, especially in areas with mixed cacti. It can live in very arid environments as long as prickly pear or cholla are available.

Feeding

• Behavior: Woodrats forage at night, eating food and carrying some items back to the house to store for later use (as is the case with mesquite beans), or to incorporate them (especially cactus parts) right into the house structure.

Life History

Woodrats are famous for their houses made of sticks, cactus parts, animal dung and debris, usually tucked in around a prickly pear cactus, under a mesquite tree or hackberry bush, or among boulders. The house acts as insulation for the nest, which is underneath but close to the ground surface. The spiny cactus parts may also offer some protection from coyotes digging up the nest. Several entrance holes allow the packrat a quick escape should a snake come visiting. Packrats are solitary, with only one rodent per household, unless a female has young.

The rats and mice are among the most sucessful mammal groups on Earth. They are adaptable creatures that can inhabit almost any environment. The Sonoran Desert, with its great diversity of habitats, is blessed with an abundance and a wide variety of these fascinating creatures. Here we have predatory grasshopper mice that hunt and kill other mice, and packrat builders that construct houses of sticks and debris up to 2 or 3 feet (1 m) high and 8 feet (2.4 m) wide. The desert woodrat lives in the most xeric (arid or dry) environments, while Merriam's mouse fills a niche in mesquite bosques.

These little rodents are at the bottom of the vertebrate food chain, preyed upon by everything from coyotes and snakes to hawks and bobcats. In response, they breed prolifically, with some species, like the cotton rats, able to produce eight to ten litters a year. Populations still fluctuate with drought and predation, but the mice and rats are able to respond to good conditions by rapidly rebuilding their numbers.

All rodents, including the mice and rats, are gnawers. Their teeth are ever-growing and must be kept trimmed down by constant gnawing. A layer of hard orange enamel covers the front surface of the teeth. The rest of the tooth is softer and wears down quicker than the enamel as the rodent gnaws, thus creating a chisel-like shape to the front teeth that is unique to the rodent family.