Part 15

This species occurs from 1000 feet elevation to above 9000 feet elevation on the Pacific slope of the Mountains, but although probably the most widespread rodent in the area it is absent from many habitats. This mouse reaches maximum abundance in the coastal sage scrub association, particularly where the soil is sandy with scattered vegetation--usually coastal sagebrush and black sage. On the foothill adobe slopes none was trapped, nor have any been taken in most of the chaparral habitats. A few gambeli were trapped amid the talus beneath growths of scrub oak and bay trees in San Antonio Canyon, at 4300 feet elevation. On Blue Ridge, at elevations of from 7200 feet to 8300 feet, this mouse inhabited areas clothed with snowbush, basin sagebrush, currant, and scattered conifers, and was found sparingly in the coniferous forests. Thus this species lives on contrasting soil types in association with many different vegetational assemblages, from the coastal base to the crest of the range.

There is a rather wide variation in color in gambeli from the San Gabriels. Certain individuals taken in open, sandy coastal sage areas are pale, some being indistinguishable from examples of sonoriensis taken in the pinyon-juniper association on the desert slope. Specimens from San Antonio Canyon have somewhat darker pelage than those from the sage belt, and than individuals taken on Blue Ridge. Possibly a large series of Peromyscus maniculatus from the San Gabriel Mountains would show definite local trends in color of pelage.

This species is active on sub-freezing and rainy nights as evidenced by trapping results, and at Big Pines there were tracks around the bases of conifers after a heavy snowfall in December, 1951. Several females taken in the sage belt in October, 1948, carried embryos, and a lactating female was recorded from Blue Ridge on November 13, 1951. Juveniles have been taken in September, October, November, and December.

Specimens examined.--Total, 9, distributed as follows: Los Angeles County: 1 mi. S and 2 mi. W Big Pines, 7400 ft., 3; 1 mi. S and 2 mi. E Big Pines, 8200 ft., 1; 4 mi. NE Claremont, 1900 ft., 2; San Antonio Wash, 1800 ft., 3 (PC).

=Peromyscus maniculatus sonoriensis= (Le Conte)

Deer Mouse

This subspecies is associated with contrasting types of soil and vegetation. It is seemingly absent from the upper pinyon-juniper sage flats and areas grown to chaparral, but is fairly common on the gravelly benches dotted with junipers, and in the washes issuing from the canyons on the desert slope. It is present in small numbers in the Joshua tree association.

In 1951 the numbers of sonoriensis were noticeably less than in 1948; probably this was correlated with the series of dry winters in this period. In December, 1948, this animal was one of the most common rodents in Mescal Wash, 200 trap-nights yielding thirteen specimens; but in November, 1951, none was taken. In parts of the juniper belt, where an average of about six sonoriensis was taken per 100 trap-nights in 1948, the average had dropped to one per 100 trap-nights in 1951.

Specimens of this species from the desert slope of the mountains have been assigned to the subspecies sonoriensis. Those from Blue Ridge tend toward sonoriensis in color, and may be considered as intergrades between this subspecies and gambeli.

This species was active on nights when the temperature was as low as 10 deg. F., and individuals were trapped in the juniper belt in December, 1948, when four inches of snow lay on the ground.

Gray-pelaged juveniles were taken on the desert slope in December, 1948, and a female taken in Mescal Canyon on December 22 of this year carried four embryos near term.

Specimens examined.--Total, 11, distributed as follows: Los Angeles County: 8 mi. E and 4 mi. S Llano, 4000 ft., 6 (4 PC); Mescal Canyon, 4800 ft., 5.

=Peromyscus boylii rowleyi= (J. A. Allen)

Brush Mouse

The main range of this mouse in the San Gabriel Mountains lies between 1600 and 6000 feet elevation on the Pacific slope of the Mountains, thus encompassing much of the chaparral and oak woodland associations. It was the most common mammal in the oak woodland association in the lower foothills and often was trapped there on leaf mold beneath the oaks. While trapping for shrews I regularly took this species in riparian growth right down to the edge of the water. In San Antonio Canyon many boylii were trapped beneath logs and dense vegetation, and on wet seepage slopes adjacent to the creek.

This species shows a definite predilection for rocky habitats where these occur in the chaparral. In heavy lilac brush near Camp Baldy Peromyscus boylii was outnumbered by P. californicus, yet where talus slopes or boulder piles occurred boylii was more numerous. At the head of Cow Canyon amid boulders beneath scrub oak, bay, and big cone-spruce, this species was especially abundant and no other Peromyscus was taken.

Of special interest is the occurrence of this mouse on the desert slope of the mountains; there it was taken beneath scrub oaks in the pinyon-juniper association at the mouth of Mescal Canyon, and amid boulder and debris piles in Mescal Wash at 4000 feet elevation. While manzanita and scrub oak grew in the wash at the points of capture, the animals were actually surrounded by the desert conditions of the Joshua woodland, and associated with such desert forms as Onychomys torridus pulcher and Peromyscus eremicus eremicus.

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 association 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 association, near Jackson Lake, at 6000 feet, to the lower limit of the association 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 association 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 Pass 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 Pass 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