GRAY BUSHY-TAILED WOOD RAT. Neotoma cinerea cinerea (Ord)

Field characters.—Size larger than Streator Wood Rat or House Rat; tail shorter than head and body, with long hairs on sides forming a flat brush (figs; 12c, 15); pelage thick and soft. Head and body 7 to 9-1/3 inches (180-237 mm.), tail 4-3/4 to 7-2/5 inches (120-188 mm.), hind foot 1-2/5 to 1-4/5 inches (40-46 mm.), ear from crown 1 to 1-1/3 inches (26-34 mm.); weight 9-1/2 to 16-1/4 ounces (271-459 grams). Coloration above sandy brown, tail somewhat darker; feet, and under surface of body and tail, pure white. Workings: Sparse accumulations of sticks and other debris in crevices among rocks. Droppings: Black, cylindrical, about 1/2 by 1/6 inch.

Occurrence.—Resident in boreal parts of Sierra Nevada. Recorded from near Gentrys (5900 feet) and Little Yosemite Valley eastward to Williams Butte. Life zone, upper Canadian and whole of Hudsonian. Lives in rock slides and in and about logs. Nocturnal; partially colonial.

The Gray Bushy-tailed Wood Rat is an inhabitant of the higher and more easterly portions of the Yosemite section and so comes only to the attention of those visitors who spend some time in the back country. When human beings do become aware of the presence of this rodent it is because the animal literally forces itself upon their attention. Campers tell many tales, some humorous, some semi-tragic, of the activities of the big 'pack-rat' or 'trade rat' among their belongings.

The range of this species is separated from that of the foothill-inhabiting Streator Wood Rat by a hiatus usually several miles in width and a gap of at least 1500 feet in altitude. The nearest approach of one to the other, according to our records, is that of streatori on the floor of the Yosemite Valley to cinerea on the slopes close above Gentrys. The main range of the bushy-tail involves the belt of country characterized by the alpine hemlock, namely the Hudsonian Zone. A few of these rats live at or above timber line, as on Mount Lyell (up to an altitude of 13,090 feet); and on the east slope of the Sierras, as at Walker Lake and on Williams Butte, they occur at much lower altitudes and in lower zones.

In the Yosemite region the Bushy-tailed Wood Rat is an inhabitant of rock slides. A very few were captured away from rocks, but only enough to emphasize the mass preference of the species for heaps of talus. There are rock slides in the Transition and Canadian zones on the west slope which to our eyes seem indistinguishable from those at higher levels, but the bushy-tails do not inhabit them. Immediate competition with the other near-related species is lacking, for the Streator Wood Rat is not found to any large extent in the Transition Zone rocks and is entirely absent from the Canadian.

When compared with the common round-tailed, house-building wood rat of the western foothills, the bushy-tail is found to be of the same general form, but it is larger and heavier, with longer fur. (See fig. 15.) The hair on its tail is elongated so that this member has something of the flat, brush-like appearance associated with tree squirrels and chipmunks. The dense body coat of the Bushy-tailed Wood Rat is doubtless an adaptation to life in a boreal region. The general configuration of the head and body of this species, especially if seen in a rock slide where the tail may be concealed, reminds one of a cony.

Fig. 15. Gray Bushy-tailed Wood Rat. Photographed from animal freshly trapped near Vogelsang Lake, August 31, 1915.

A feature of this wood rat is the musty odor which is associated with both the animal and its home precincts. This odor is produced by glands at the side of the anus, a condition similar to that obtaining in the skunk. Places which are continuously inhabited by the bushy-tail take on this odor, the presence of which furnishes a clue to naturalists who may be hunting for places to trap the animals.

The present species like its foothill relative is essentially a night prowler. The rat traps, baited with rolled oats, which we set in rock slides at elevations above 8000 feet trapped conies during the daytime and Bushy-tailed Wood Rats at night. On but one occasion did we see a Bushy-tailed Wood Rat abroad during the daytime. On July 18, 1915, four members of our field party had ascended to the summit of Mount Lyell, and while we were eating lunch there a bushy-tail came forth and gathered lunch scraps which we and previous visitors had dropped. Bits of hardtack scattered on the rocks were eagerly sought and devoured, though the rat retired into a crevice to chew them up. No general source of natural food was to be seen on the peak.

This species is less of a builder than its foothill cousin. Nowhere did we find the large accumulations of material that the Streator Wood Rat gathers. In a few places bushy-tails had accumulated twigs, sticks, old bones, and similar material in crevices among the rocks, much after the manner of the Streator Wood Rat in the boulder taluses of Yosemite Valley. But many of the localities inhabited by the bushy-tail were entirely devoid of building material of any sort. Since there are, in such places, many crevices within the rocks in which the animals may take shelter, they have, perhaps, no need to build elaborately. In those cases where we saw no external evidences of a nest, there may have been inhabited shelters deep down among the rocks where human beings and the larger carnivores could never penetrate.

The young of the Bushy-tailed Wood Rat are produced during the mid-summer season. One female, taken in Lyell Cañon on July 17, 1915, contained 3 embryos. The females have only four teats, which suggests that the litters are small. Several females captured between July 9 and 21, 1915, gave evidence of having recently suckled young. By the last week of August young were being trapped in considerable numbers and were then from one-fourth to one-half the weight of the parents. Their juvenal pelage is very soft and short and lacks the prominent sandy brown overcast seen on adult animals. At this age the tail is only beginning to show the lengthened hairing at the sides and end.