Pack Rat or Trade Rat is the name commonly applied to this individual, represented in the park by both of the above forms. Pest of the stations and patrol cabins because of his fondness of getting into buildings and collecting items of every description, especially those of shiny appearance. These are packed to his nest, which is located either in rock piles, cliffs or whenever possible in or around buildings. He cuts open food containers, bedding and other contents and makes a general mess.
He frequently leaves some object in place of the stolen article, hence the name trade rat. However, this trade is probably due to his dropping something that he was already carrying, when he spied the new object that was more attractive, rather than any desire to make a fair trade. They gather anything that is of a convenient size to carry.
The wood rat is a very clean animal, of no relation to the common barn rat except in superficial resemblance. A vegetarian in diet he lives on green vegetation such as grass and foliage, fruit, bark, roots, fungi, seeds and nuts. He is active all year but seldom accumulates much of a store of winter food.
Mainly nocturnal in habit, they are, however, occasionally seen in the daytime. Their principal enemies here are hawks, owls, weasels, coyotes and martens.
The young, from three to six in a litter, are born in June or July and are duller in color than the parents.
General description: Large in size, mouse-like in appearance. The fur is fairly long, soft and grayish buff in color, darker in the Colorado form, on the upperparts, white underparts and feet, and a large, bushy, flattened almost squirrel-like tail. Total length 15 to 16 inches. Sexes equal in size.
Wood Rat or Rock Rat
Where found: Throughout the park. The gray wood rat mainly in the transition zone in open country along the Yellowstone, Lamar and Gardner Rivers and around Mammoth. Colorado wood rat in higher portions of the park.