KANGAROO RATS. Genus Dipodomys¹³

Field characters.—Body size between that of House Mouse and House Rat, nearer the latter (see footnote 13 for detailed measurements); tail exceeding head and body in length, well haired, and with a conspicuous tuft at end (pl. 26e); front feet very small, hind feet and legs disproportionately long and large; ear rounded, held close to side of head; a large fur-lined cheek pouch on each side of face opening outside of mouth; eyes large; pelage silky. Coloration above plain sandy brown (varying in tone according to subspecies); a white stripe across each thigh; whole under surface of body pure white; end of nose white with a blackish crescent on each side; tail four-striped—dark stripe above and below, with an intervening white stripe on each side. Workings: Burrows about 2 inches in diameter, in loose soil, usually about bases of bushes; entrance hole usually filled with earth during the daytime. Tracks: Paired impressions of hind feet (3 or 4 toes showing forward, connected with a long heel print) in lengthwise series at intervals of 7 to 36 inches, the tail track as an interrupted line midway between the footprints (pl. 40c).

Occurrence.—Resident along east side of San Joaquin Valley, at Snelling, near Merced Falls, and below Lagrange (dixoni), in western foothills about Coulterville (heermanni), and again east of the Sierra Nevada around Mono Lake (leucogenys).¹³ Nocturnal.

---

¹³Three races of Kangaroo Rats are found in the Yosemite region. They are distinct from one another structurally and occupy separate geographic areas, yet their habits and general appearance are much alike.

HEERMANN KANGAROO RAT, Dipodomys heermanni heermanni (Le Conte). Found along the west base of the central Sierra Nevada. It was recorded from 1 mile west of Coulterville to 6 miles east of that place, and probably occupies a much wider range than this indicates. It inhabits the Upper Sonoran Zone, ranging locally into the lower margin of Transition, and lives chiefly amid chaparral. Head and body 4-1/4 to 4-7/8 inches (108-123 mm.), tail 6-1/2 to 7-3/8 inches (165-187 mm.), hind foot about 1-3/4 inches (43-44 mm.), ear from crown about 1/2 inch (12-16 mm.), weight about 2-1/2 ounces (68.6-72.8 grams).

MERCED KANGAROO RAT, Dipodomys heermanni dixoni (Grinnell). A subspecies inhabiting the east side of the San Joaquin Valley (Lower Sonoran Zone). It was recorded at Snelling, near Merced Falls, and below Lagrange. It inhabits open sandy or dusty places. From heermanni it is distinguished by smaller size and average lighter color. (See pl. 26e). Head and body 3-7/8 to 4-3/4 inches (98-119 mm.), tail 6 to 6-7/8 inches (155-174 mm.), hind foot about 1-5/8 inches (39-42 mm.), ear from crown about 1/2 inch (12.5-14 mm.), weight 1-1/2 to 2-2/5 ounces (43.4-68.4 grams).

PALE-FACED KANGAROO RAT, Dipodomys leucogenys (Grinnell). A species distinct from the two preceding in several particulars, and readily separated from them by larger size and paler coloration. It is rather common at Mono Mills, on the slopes of Mono Craters and along Dry Creek; all these localities are near Mono Lake east of the Sierra Nevada. It inhabits sandy places among the sagebrush. Head and body 4-5/8 to 5-1/2 inches (117-140 mm.), tail 6-1/3 to 7-1/3 inches (160-185 mm.), hind foot about 1-3/4 inches (44-47 mm.), ear from crown about 1/2 inch (12-13 mm.), weight 2-3/4 to 3-1/8 ounces (78.2-88.5 grams).

---

The Kangaroo Rat is a type of mammal which has developed in response to the sandy desert conditions obtaining in the southwestern part of North America. The territory at either end of the Yosemite cross-section, being rather arid in character and otherwise suitable, is occupied by a moderate population of this rodent. The name kangaroo rat refers to the mode of progression which, like that of the Australian kangaroo, is accomplished by catapultic leaps with the long hind legs and feet, in which operation the greatly lengthened tail acts as a stabilizer and support. Another special feature, the external fur-lined cheek pouch on each side of the face, used, as with the pocket gopher, for the storage of clean food materials, has led to the name pocket rat for this rodent.

Further description of the kangaroo rat may be of interest, particularly as the animal itself is rarely seen in the wild alive though it has been found to submit readily to captivity. The form is somewhat tapered, the nose being pointed and leading back to a rather flattish head. The forelegs and feet are small, but the hind legs and feet, the leaping apparatus, comprise quite the largest part of the animal (pl. 26e). The tail is long, well exceeding the head and body in length, and is covered with hair which, toward the tip, becomes long and forms a tuft, or better, a 'brush.' The nose is provided with an elaborate set of vibrissae or 'whiskers,' the longest of which reach out far beyond the side of the body. The ears are rather small though the hearing ability of these animals is probably acute to judge from the enlargement of the back portions of the skull which house the internal ear structures. The whole pelage of the animal is soft, even silky in texture. The kangaroo rat habitually travels and rests on its hind feet, the fore ones being devoted to the handling of food materials and to cleaning the fur.

Most species of kangaroo rats inhabit sandy situations, so that, as a rule, naturalists have come regularly to look for the animals in such places. The Merced and Pale-faced kangaroo rats of the Yosemite region frequent sandy ground. But the Heermann Kangaroo Rat which lives in the western foothill country dwells in the chaparral where there is seldom any sand and where usually the ground is gravelly or even rocky in nature. Its niche is evidently much like that of the California Pocket Mouse. The special requirement of the kangaroo rat is a location in which it can place its burrow; the animal does all its foraging out on the surface of the ground. No burrows were opened up by us in the Yosemite region, but in other places the underground retreats have been found to be of relatively simple nature, used as shelters during the daytime and in cold or rainy weather, and as storehouses for food to be eaten when the animals cannot well venture out.

The distance which a kangaroo rat can cover in one leap is apt to be over-estimated. On any of the relatively few occasions when we have seen one of these animals abroad during the daytime, it has made off so suddenly that we were practically at a loss to describe what transpired during the few seconds that the animal continued in sight. In cases where the actions of an animal have been observed successfully the extent of a single leap has been found to be moderate; one jump followed another so rapidly, however, that the rat's progress was amazingly swift. Speedy escape is likely to be interpreted as due to the animal's ability to jump prodigious distances, whereas the real basis is rapidity of action. Animals frightened or turned out of their burrows when ground was being plowed have been seen to cover 3 to 4 feet at a leap. Under extremely favorable circumstances this might be slightly exceeded. The tracks of an undisturbed Heermann Kangaroo Rat seen in a dusty road near Coulterville were (heel to heel) from 7-1/2 to 9 inches (190-230 mm.) apart. Where something in the road had claimed its attention and the animal had loitered the tracks were even closer. (Sec pl. 40c).

The normal activity of the kangaroo rat is confined to the hours of darkness. Unless disturbed by man or some native enemy, it rarely or never ventures out in the daytime. But as soon as dusk has fallen it leaves its burrow and goes hunting for food. The animal subsists almost entirely upon small seeds of particularly sought kinds. Material is gathered and stuffed into the cheek pouches, then the rat retires to its burrow where the food materials are deposited in a special chamber, to be shucked out and consumed at leisure. Examination of the cheek pouch contents of captured animals indicates that a variety of wild seeds are used as food; but when cultivated grains are available the animals turn to these, especially where the fields adjoin wild land. Kangaroo rats readily take the poisoned grain put out for ground squirrels and many meet death from this cause. Ploughing of new land destroys their burrows and quickly drives them out, so that this rodent rarely becomes an important enemy of man.

Our specimens of the Heermann Kangaroo Rat were all taken in the neighborhood of Coulterville, from Blacks Creek on the west to Smith Creek, 6 miles east of the town. But the species enjoys a much wider local range, for we found tracks in the dust of roads at Pleasant Valley, closed burrows on the greasewood slopes about El Portal in December (when the rats are loath to come forth), and got reports of the presence of the animals in fields near the town of Mount Bullion. It was our experience that this chaparral-inhabiting species was more difficult to trap than those which live on the sandy plains and deserts. Furthermore, the population of heermanni is sparser than that of the other species; perhaps two to the acre would represent the population on favorable slopes. In a few places, as about clearings in the chaparral, there are probably somewhat more than the number indicated.