Mammals of the San Gabriel Mountains of California Part 9

Immature individuals were taken in October, November, February, and March, and a female with two large embryos was taken near Icehouse Canyon on November 8, 1951.

_Specimens examined._--Total, 8, distributed as follows: Los Angeles County: Mescal Wash, 4000 ft., 1; Mescal Canyon, 4800 ft., 2; San Antonio Canyon, 5200 ft., 2; San Antonio Canyon, 4500 ft., 1; San Antonio Canyon, 2800 ft., 1; Thompson Canyon, 1800 ft., 1 (PC).

=Peromyscus truei montipinoris= Elliot

Pinon Mouse

Only once was this mouse found outside the pinyon-juniper a.s.sociation of the desert slope; in November, 1949, several were collected near Cajon in mixed manzanita, scrub oak, and greasewood chaparral. This was the only _Peromyscus_ of regular occurrence in the pinyon-juniper area, and was recorded from the upper limit of this a.s.sociation, near Jackson Lake, at 6000 feet, to the lower limit of the a.s.sociation at the mouth of Graham Canyon at roughly 4000 feet elevation.

Although in the juniper belt _truei_ often occurs on common ground with _Peromyscus maniculatus sonoriensis_, the habitat preferences of these animals are generally complementary. Where the mice occur together, traps set in a variety of locations caught _Peromyscus maniculatus_, but typically traps set amid the brush or on the open ground away from the junipers were productive. On the contrary _truei_ was invariably trapped quite near the junipers and often in a.s.sociation with the large nests of _Neotoma fuscipes simplex_. In fact traps set right on the beds of litter beneath the junipers were most likely to catch _truei_. Records kept of trapping localities show that _truei_ was without exception trapped within twenty feet of some treelike shelter such as junipers, pinyons, Joshua tree or scrub oaks. Thus _Peromyscus maniculatus_ occupies the open stretches between the trees, while _truei_ inhabits the ground beneath and immediately adjacent to the trees. In Nevada the pinon mouse prefers rocky areas (Hall, 1946:520).

In the San Gabriel Mountains this mouse does not seem to have this predilection.

In the juniper belt _truei_ was second to _Dipodomys panamintinus_ in point of numbers. In the course of 500 trap-nights in the juniper belt twenty-two _truei_ were taken with thirty-six _Dipodomys_.

I consider my series of _Peromyscus truei_ from the desert slope of the San Gabriels to represent the subspecies _montipinoris_. The series is closely comparable to specimens of the subspecies _montipinoris_ in the California Museum of Vertebrate Zoology from the Mount Pinos area, but differs from specimens of the race _chlorus_ from the San Bernardino Mountains in certain diagnostic characteristics. In his recent paper on _Peromyscus truei_, Hoffmeister (1951) considered the populations of this species in the San Gabriels to be of the race _chlorus_.

Hoffmeister had only one specimen available from the San Gabriel Mountains (Lytle Creek, on the Pacific slope) which was intermediate between _montipinoris_ and _chlorus_, but on the basis of cranial measurements it was referred to the race _chlorus_. Specimens of _Peromyscus truei_ from the eastern end of the desert slope of the San Gabriel Mountains and the Cajon Pa.s.s area would probably demonstrate that the race _montipinoris_, which occupies the desert slope of the San Gabriels, intergrades with the race _chlorus_, which occurs in the San Bernardino Range immediately to the east, in the Cajon Pa.s.s area.

Although _montipinoris_ occurs on the desert slope of the San Gabriels, _chlorus_ may occur on the Pacific slope. I took no specimens of the pinon mouse on the Pacific slope of the San Gabriel Mountains.

In December, 1948, many small juveniles were taken in the juniper belt, and on October 15, 1951, two females trapped at the head of Grandview Canyon had embryos: one three and the other four. On November 13, 1951, a partially gray-pelaged subadult female was trapped which had recently suckled young.

_Specimens examined._--Total, 17, all in Illinois Museum of Natural History, distributed as follows: Los Angeles County: Mescal Canyon, 4500 ft., 8 mi. SE Llano, 11; Mescal Canyon, 4300 ft., 2; 6 mi. SE Valyermo, 5100 ft., 1; Grandview Canyon, 6 mi.

SE Valyermo, 5100 ft., 1. San Bernardino County: 1 mi. W Cajon, 3200 ft., 2.

=Onychomys torridus pulcher= Elliot

Southern Gra.s.shopper Mouse

Gra.s.shopper mice seemed to be partial to the more sandy parts of the Joshua tree flats where the mice were trapped regularly but not abundantly. This mouse inhabited the barren sandy channels of Mescal Wash but was rare on the adjacent juniper-clad benches. In the arid, sandy washes this typical desert rodent penetrated the high pinyon-juniper a.s.sociation.

Wherever gra.s.shopper mice occurred they were outnumbered by most of the other rodent species. For example, on November 26, 1949, below Graham Canyon, 100 snap traps yielded 10 _Dipodomys panamintinus mohavensis_, 2 _Dipodomys merriami merriami_, 4 _Peromyscus maniculatus sonoriensis_, and 3 _Onychomys torridus pulcher_.

Where abandoned kangaroo rat burrows were common in the Joshua tree belt these burrows were used as retreats by _Onychomys_. Some traps set at the entrances to old burrows caught gra.s.shopper mice.

_Specimens examined._--Total, 7, distributed as follows: Los Angeles County: 8 mi. E and 3 mi. S Llano, 3500 ft., 1; Mescal Wash, 4200 ft., 5 (3 PC); 2 mi. S Valyermo, 4600 ft., 1 (PC).

=Neotoma lepida intermedia= Rhoads

Desert Woodrat

This species was on the Pacific face of the Mountains from 1600 feet elevation in the coastal sage belt, to 4800 feet elevation in open groves of big cone-spruce and scrub oak of the chaparral a.s.sociation.

The local distribution of this woodrat is determined by suitable nesting sites. Although taken in different types of vegetation, _lepida_, without exception, was a.s.sociated with rocky areas or areas supporting patches of p.r.i.c.kly-pear cactus. In the channels of San Antonio Wash, _lepida_ was commonly a.s.sociated with jumbles of boulders and boulder-dotted cut banks. There the vegetation is spa.r.s.e, and the rats dwell among the rocks; only their droppings and faint trails indicate their presence. Among boulders _lepida_ builds only small houses of sticks and debris, and even these only occasionally. The effect of the p.r.i.c.kly-pear cactus on the distribution of _lepida_ in the sageland is striking; trap lines there yielded no woodrats where extensive rock piles and patches of p.r.i.c.kly-pear were absent, but many rats were taken where patches of p.r.i.c.kly-pear are plentiful. On an acre supporting coastal sagebrush at the mouth of San Antonio Canyon, at 1800 feet elevation, there were fourteen patches of p.r.i.c.kly-pear, each covering at least thirty square feet. In these patches there were thirteen occupied woodrat nests. Only one patch lacked an occupied nest, and this one contained the remains of an old nest. On this acre there were at least thirteen individuals. In the sagebrush belt only an occasional large patch of cactus lacks a woodrat house occupied by _lepida_. Seemingly _Neotoma fuscipes_ does not build houses in patches of p.r.i.c.kly-pear.

Most of the houses built by _Neotoma lepida_ are small and simple as compared to those of _Neotoma fuscipes_, and often in rocky areas no nests are in evidence. The most elaborate nests are built among the pads and spines of the p.r.i.c.kly-pear and under laurel sumac or other large shrubs growing near washes. One of three houses examined at the mouth of San Antonio Canyon was on sandy ground in a patch of _Opuntia_ measuring approximately 11 x 14 feet. The house was 14 inches high and 41 x 37 inches at the base. It was built around the main stem of the p.r.i.c.kly-pear and a rock about 10 inches in diameter. The house was constructed of sticks of coastal sagebrush and buckwheat, and was dotted with dissected fruits and flowers of the p.r.i.c.kly-pear. The main chamber was arched over by the main stem of the p.r.i.c.kly-pear and was roughly 12 x 19 inches, inside dimensions, being reached through two three-inch openings, one on the east side of the chamber and one on the north side of the chamber. Two cup-shaped nests were inside the chamber, these being constructed mostly of gra.s.ses, and each resembling a well constructed bird nest 4 inches in diameter. The gra.s.s nests were free of feces, but feces were piled up against the west side of the chamber with many snail sh.e.l.ls and dissected fruits and flowers of p.r.i.c.kly-pear.

Thirty-five inches from the main chamber was a third gra.s.s nest on the ground beneath a cl.u.s.ter of cactus pads. Next to this there was a blind burrow about eight inches long, and one and three-quarters inches in diameter. No burrow led to the main chamber, in this or in either of the other houses, but all had at least one short blind burrow beneath the house.

At many houses there were one to three gra.s.s nests outside the house on the ground, within four feet of the house. From each nest a well worn path lead to the house. Traps set in these nests invariably caught woodrats.

The many p.r.i.c.kly-pear fruits and snail sh.e.l.ls in and around the houses of _lepida_ probably were remnants of food. So many of the rodents caught in traps near woodrat nests were partly eaten--usually the brains were taken--that I suspect the woodrats of eating their relatives. The heads of many composite annuals were piled near woodrat nests.

Immature individuals were taken in September, October, and early November, and on September 26, 1951, a lactating female was trapped near Palmer Canyon.

An old female bobcat trapped in Thompson Canyon had ma.s.ses of cactus thorns beneath her skin, especially about the forelegs. These thorns were probably received while she was foraging in growths of p.r.i.c.kly-pear for woodrats. The other bobcats from San Antonio Wash also had acc.u.mulations of thorns under the skin of the forelegs. Fragments of the skulls of _Neotoma lepida_ were recovered from horned owl pellets and coyote feces.

_Specimens examined._--Total, 7, distributed as follows: Los Angeles County: San Antonio Canyon, 4500 ft., 2; San Antonio Wash, 1800 ft., 5 (2 PC).

=Neotoma lepida lepida= Thomas

Desert Woodrat

These woodrats were present in rocky situations along the desert slope from the lower edge of the juniper belt down into the desert. Specimens were taken in piles of boulders in Mescal Wash, and amid rock outcroppings on the steep, barren, south slopes at the base of Grandview Canyon, whereas none was found on the juniper-clad benches.

This woodrat built no nests in rocky areas; however, in the Joshua tree belt _N. l. lepida_ often built small nests at the bases of large standing or prostrate Joshua trees. There sticks from creosote bushes, along with cow dung and small stones were favorite building materials.

Judging from the large number of unused woodrat nests in the Joshua tree flats it seemed that this rat was formerly far more common than it was in the period of this study.

_Specimens examined._--Total, 9, distributed as follows: Los Angeles County: 6 mi. E and 1 mi. S Llano, 3500 ft., 4; Mescal Wash, 4200 ft., 5 (3PC).

=Neotoma fuscipes macrotis= Thomas

Dusky-footed Woodrat

This subspecies was widely distributed along the coastal slope of the mountains from the coastal sage belt, at roughly 1600 feet, up to 6500 feet at the lower edge of the yellow pine forest and was most common in the chaparral a.s.sociation.

In the coastal sage belt these woodrats are restricted to wash areas where large chaparral plants such as lemonadeberry and laurel sumac are used as nesting sites. In San Antonio Wash the occasional large juniper trees almost invariably harbor the nests of _fuscipes_. The general absence of suitable nesting sites in the sage belt probably limits the spread of _fuscipes_ in this area.

In the upper part of the chaparral belt in talus these woodrats live beneath the angular boulders and build no visible houses. Several areas of talus occupied by woodrats were examined carefully and no sign of houses was noted.

Two juveniles were found in the stomach of a rattlesnake (_Crotalus viridis h.e.l.leri_) killed in May, 1948, at the mouth of Evey Canyon.

Remains of woodrats were found in feces of the coyote and gray fox.

Lactating females of this species were taken on March 16, and October 2, 1951.

_Specimens examined._--Total, 4, distributed as follows: San Bernardino County: Icehouse Canyon, 5500 ft., 2. Los Angeles County: San Antonio Canyon, 2800 ft., 2.

=Neotoma fuscipes simplex= True

Dusky-footed Woodrat

These rats were recorded from the yellow pine forests on Blue Ridge, at 8100 feet, down to the lower edge of the juniper belt, at 3800 feet.

Their presence there as elsewhere was determined by the occurrence of adequate cover. On Blue Ridge they were taken in and near patches of s...o...b..ush, currant, and choke cherry, and one was taken beneath a pile of logs where no nest was in evidence.

The thickets of choke cherry in hollows on Blue Ridge were favored house-building sites of woodrats. Among the tangle of branches large nests were built, and in September, 1951, the remains of choke cherry fruit and gnawings on the limbs of these plants indicated that woodrats were active throughout these extensive patches of brush.