Mammals of the San Gabriel Mountains of California Part 7

This species prefers barren slopes supporting yucca plants. These plants produce large seeds which are staple food items for _P. f. pallidus_ and other rodents during the lean part of the year, that is to say, late summer and autumn. Many of the dry capsules of the yucca plants were examined in October, 1951, and these generally still contained a few seeds. Pocket mice taken in October usually carried in their cheek pouches seeds of yucca together with some other material, and often they carried only the seeds of yucca. Probably the wind shakes only a few seeds out of the capsules at a time, thus tending to drop the seeds over a fairly long period.

Trapping in winter in the juniper belt revealed that these pocket mice were not active above ground on nights colder than about 40 F. On nights when the temperature was about 36 F. none was taken, but on the one night in late December, 1948, when the minimum was 44 F., several specimens were taken. In this same area in May 1949, pocket mice were the most numerous rodents. Because of their evident sensitivity to cold weather, these mice must remain below ground for weeks at a time during the cold weather of December and January.

Specimens of _pallidus_ from the desert slope of the San Gabriels are grayer (less brown) than specimens taken farther southeast in the Mojave and Colorado deserts. Further sampling of populations of _Perognathus fallax_ from areas adjacent to the San Gabriels might demonstrate differences of sufficient magnitude to warrant subspecific distinction of the San Gabriel population. Possibly, however, the San Gabriel series manifests only local variation in the race _pallidus_. Grinnell (1933:54) characterizes the ecological niche of the race _pallidus_ as being "open, sandy ground, often ... surrounded by rocky slopes,"

whereas these pocket mice in the San Gabriels inhabited gravelly or rocky juniper-dotted benches.

_Specimens examined._--Total, 11, distributed as follows: Los Angeles County: 5 mi. E and 4 mi. S Llano, 4500 ft., 7; 2 mi. E Valyermo, 4500 ft., 3; 4 mi. E Valyermo, 5000 ft., 1.

=Perognathus californicus dispar= Osgood

California Pocket Mouse

Mice of this subspecies were recorded from the lower chaparral a.s.sociation below about 4000 feet elevation along the coastal face of the San Gabriel Range. They were trapped on greasewood-covered slopes, in mixed growths of white sage and buckwheat, and beneath scrub oak and lilac chaparral; however none was taken in the heavy chaparral of the upper parts of the chaparral a.s.sociation.

One small juvenile in gray pelage was taken in San Antonio Canyon on October 1, 1951.

_Specimens examined._--Total, 5, distributed as follows: San Bernardino County: Lytle Canyon, 4000 ft., 2 (PC). Los Angeles County: San Antonio Canyon, 3000 ft., 3.

=Perognathus californicus bernardinus= Benson

California Pocket Mouse

On Blue Ridge these mice were recorded between 7100 and 8000 feet elevation. Here they were restricted to dense tracts of s...o...b..ush and sagebrush, often where these tracts were interspersed with, or beneath, open groves of conifers. These mice seemed to favor areas where this thick brush was broken by patches of open, gra.s.s-covered ground. Benson (1930:450) records this subspecies from Swarthout Valley, near Big Pines, at 6860 feet elevation.

While setting traps for pocket gophers one mile southwest of Big Pines, in September of 1951, I frightened a pocket mouse from its burrow. The animal jumped into the tangle of interlacing twigs of a nearby clump of s...o...b..ush, and with great dexterity climbed into the center of the bush, where it was lost to view. I was surprised at the facility with which this saltatorial rodent traveled through the network of small branches.

In winter, in areas inhabited by this mouse, snow covers the ground for long periods during which these mice are probably forced to remain below ground.

_Specimens examined._--Los Angeles County: 1 mi. S and 2 mi. W Big Pines, 7400 ft., 2.

=Dipodomys panamintinus mohavensis= (Grinnell)

Panamint Kangaroo Rat

This rat is common in the Joshua tree and juniper belts, and locally penetrates the pinyon belt at about 5000 feet elevation. It occurs regularly along the entire desert slope of the San Gabriel Mountains.

The upper limit of the range of this species roughly coincides with the upper limit of the juniper belt, and within this range it was found to inhabit areas having widely different soil types. It occurred on the sandy ground of desert washes, the gravelly soil of the juniper-clad benches, and the mixed sandy and rocky ground of washes in canyons. A preference is shown by _panamintinus_ for fairly level ground. Rough terrain or steep slopes are generally avoided, whereas rather large colonies of these kangaroo rats are found in small flats of the desert foothills.

Below about 4500 elevation on the interior slope this species was the most numerous rodent, and seemed to reach maximum abundance in the Joshua tree a.s.sociation. About 500 trap-nights in the juniper belt near Graham Canyon yielded 31 specimens, whereas about 300 trap-nights in Joshua tree flats took 34 individuals.

The cheek pouches of many specimens taken in early winter contained green shoots of gra.s.s and little dry material. On many occasions rat traps set next to wood rat nests beneath large junipers produced _panamintinus_, and many of these animals had their cheek pouches crammed full of juniper berries.

In December, 1948, _panamintinus_ was trapped consistently on nights when the temperature dropped to below 20 F. On December 27, 1948, after a three inch snowfall, tracks of this species were noted in the snow at the mouth of Mescal Canyon.

Parts of the skulls of this species were found in many coyote feces from the desert slope.

_Specimens examined._--Total, 11, distributed as follows: Los Angeles County: Mescal Wash, 4000 ft., 8 (6 PC); 2 mi. E Valyermo, 4600 ft., 3.

=Dipodomys merriami merriami= Mearns

Merriam Kangaroo Rat

This kangaroo rat barely enters the area under consideration and is almost restricted to the Joshua tree a.s.sociation, for only a few individuals were taken at the lower edge of the juniper benches. This species inhabits the Joshua tree belt all along the desert base of the San Gabriels.

As mentioned in the description of the Joshua tree a.s.sociation, the relative numbers of _Dipodomys merriami_ and _D. panamintinus_ s.h.i.+fted from 1948 to 1951, possibly concurrent with the seasons of low rainfall in this period. Whereas in 1948 _merriami_ was decidedly less abundant than _panamintinus_ in the Joshua tree belt, in 1951 the numbers were reversed.

In December, 1951, it was found by tending the traps in the early evening that _merriami_ foraged fairly early before the ground had frozen solidly.

_Specimens examined._--Los Angeles County: 2 mi. NW mouth of Graham Canyon, 3500 ft., 5 (PC).

=Dipodomys merriami parvus= Rhoads

San Bernardino Kangaroo Rat

One specimen of this subspecies was trapped on November 26, 1951, in a sandy channel of Cajon Wash near Devore beneath a clump of scale-broom.

=Dipodomys agilis agilis= Gambel

Pacific Kangaroo Rat

This species was found below about 4000 feet elevation all along the coastal face of the range and reached maximum abundance in the level tracts of coastal sage. It was one of the most abundant rodents there, usually being second to _Perognathus fallax_ in point of numbers. Large colonies of kangaroo rats occurred locally on sandy ground adjacent to large washes. The rats were found sparingly on the foothill adobe banks and in the greasewood chaparral of the lower foothills, but in heavy chaparral where a layer of plant debris covered the ground, such as on north slopes grown to scrub oak and lilac, kangaroo rats were completely absent. Thus, in the lower chaparral belt, this rodent had a discontinuous distribution.

The coyote probably is one of the major predators of these kangaroo rats; remains of this rodent were often found in coyote feces, and coyotes excavated many burrow systems in large kangaroo rat colonies in the sandy ground near San Antonio Wash. The soil there is so soft that coyotes probably were often successful in digging out their prey. The shed skin of a large Pacific rattlesnake (_Crotalus viridis h.e.l.leri_) was found four feet inside the mouth of a kangaroo rat burrow; probably this reptile preys on _agilis_. Great horned owls (_Bubo virginia.n.u.s pacificus_) come down nightly from the chaparral to hunt in the sage flats. Beneath the perches of these owls I have found pellets containing bones of _agilis_.

_Specimens examined._--Total, 13, distributed as follows: Los Angeles County: San Antonio Wash, 1900 ft., 11 (10 PC); 4 mi. NE Claremont, 1600 ft., 2.

=Dipodomys agilis perplexus= (Merriam)

Pacific Kangaroo Rat

All the specimens of this species from the desert slope of the San Gabriel Range are referred to the subspecies _perplexus_. They were taken in brushy habitats between the elevations of 4500 and 7400 feet.

Throughout much of this area _perplexus_ was found only in certain restricted areas more or less surrounded by inhospitable ground. For example, at 7400 feet on Blue Ridge, they were found occasionally in the strips of sagebrush and lilac brush which locally capped this ridge.

Often these patches of chaparral on Blue Ridge were surrounded by areas unsuitable for kangaroo rats: on the Pacific slope, talus, oaks, and yellow pines prevailed; on the ridge scattered yellow pine groves were present; and on the steep desert slope there were yellow pines and white firs. In Swarthout Valley _perplexus_ was found in flats that supported basin sagebrush and _Haploppus_, while the coniferous forests to the south, and pinyon-covered slopes to the north were uninhabited. On flats supporting antelope brush and juniper, _perplexus_ was often common, but it did not penetrate the chaparral of adjacent slopes grown to scrub oak and mountain-mahogany. In general then, _perplexus_ was found in fairly open brushy flats or slopes, even where these were surrounded by unsuitable habitats.

Specimens of _D. agilis_ from the desert slope two miles east of Valyermo are referrable to the subspecies _perplexus_. A series taken in Cajon Wash at Devore, on the Pacific slope, is intermediate between _agilis_, of the coastal slope of the San Gabriels, and _perplexus_ of the desert slope, but approaches more nearly the later subspecies. Thus, different subspecies of _D. agilis_ occur on opposite slopes of the San Gabriel Mountains, with intergradation taking place in the Cajon Pa.s.s area and probably also at the west end of the Mountains.

Both scrub oak acorns and juniper berries were found in the cheek pouches of this subspecies, and one immature individual taken in Swarthout Valley had its cheek pouches stuffed with approximately 550 seeds of brome gra.s.s.

On November 13, 1951, at 7500 feet on Blue Ridge, a small juvenile was taken; it must have been born not earlier than September.

_Specimens examined._--Total, 17, distributed as follows: Los Angeles County: 2 mi. E Valyermo, 4600 ft., 3; 5 mi. E Valyermo, 1; 1 mi. E Big Pines, 6600 ft., 6; 1 mi. S and 2 mi. W Big Pines, 7400 ft., 2. San Bernardino County: Cajon Wash, 1/2 mi.

SW Devore, 2200 ft., 5.