The numerous species of mice of the genus Peromyscus in North America include a great variety of little beasts, many of which are distinguished by beauty of form and color. One of the most striking and picturesque individualities among these is found in the big-eared rock mouse, which is characterized by its great ears, a thick, soft coat of buffy brown fur, and a long, well-haired tail. In size it exceeds the common house mouse and even the white-footed mice which share its haunts.
This rock mouse is indigenous to the mountainous regions of the West, from Colorado and New Mexico to the Pacific and south to the Cape Region of Lower California, and down the Sierra Madre of Mexico to Oaxaca. Within this area it divides into several not very strongly marked geographic races.
As implied by its common name, it is a characteristic dweller among cliffs and ledges along the mountain slopes or rocky canyon walls, where it occupies the many crevices and little caves. In California it ranges from near sea-level up on the mountains to above 10,000 feet altitude. Although showing a distinct preference for rocky places, when available, some races of this mouse adapt themselves to other conditions and may be found on brush-grown flats, where they live in brush heaps, old wood-rat nests, and similar shelter.
That they make their homes in places other than cliffs in New Mexico was evidenced by a thick, soft nest made almost entirely of wool, found in a hollow juniper. They have several litters of from two to six young each year, the breeding period extending from spring to fall.
In Arizona and New Mexico I found the rock mouse most numerous in the belt of junipers and pinyons and in the adjacent yellow-pine forest. The crevices of cliffs about the Moki and Zuni Indian pueblos and in all the rocky wilderness of that region, including the Grand Canyon, are abundantly populated with them.
They search every nook about their haunts and often visit cabins or temporary camps for food, but do not usually take up their abode in them as do the white-footed mice. When foraging their movements are quick, and when startled they make surprisingly long leaps. Like others of their kind, they eat a great variety of seeds and small nuts, quantities of which they lay up in winter stores. Pinyon nuts, and especially juniper seeds, are their favorite food.
While of nocturnal habits, rock mice at times wander forth in sheltered spots by day, and on the few occasions I have seen them I have been delighted with their grace and beauty, their great ears and prominent shining black eyes lending them an attractive air of alert intelligence.
Throughout their lives they are in deadly peril from predatory foes. Hawks and owls glide shadowlike along the faces of their rocky homes ready to pick them up whenever they venture into open view, while bobcats, skunks, and weasels prowl about by night hunting their furry victims.
THE BROWN RAT (Rattus norvegicus and its relatives)
(For illustration, [see page 531])