Mammals of the San Gabriel Mountains of California Part 8

Family CRICETIDAE

=Reithrodontomys megalotis longicaudus= (Baird)

Western Harvest Mouse

This species inhabited gra.s.sy areas of the coastal sage belt, and reached maximum abundance on cleared land grown thickly to weeds and scattered brush. The mouse was only locally abundant--being scarce throughout much of the sage belt--but was found under contrasting conditions. In San Antonio Wash the species was taken among rocks and spa.r.s.e weeds, at Palmer Canyon specimens were trapped on a barren ridge spa.r.s.ely clothed with greasewood and white sage, and also one mile E of Big Pines in flats supporting basin sagebrush and a fairly dense growth of gra.s.ses. The western harvest mouse was recorded from 1500 feet elevation to 3200 feet on the Pacific slope, and at 6600 feet near Big Pines on the desert slope.

Those specimens of harvest mice from near Big Pines may be grading toward the desert race _megalotis_; my series of specimens from this locality, however, is too small for clear indications on this point.

Individuals in juvenal pelage were taken on November 26, 1951, near Devore.

_Specimens examined._--Total, 6, distributed as follows: Los Angeles County: 1 mi. E Big Pines, 6600 ft., 2; Palmer Canyon, 2000 ft., 1; 4 mi. N Claremont, 1700 ft., 3 (PC).

=Peromyscus eremicus eremicus= (Baird)

Cactus Mouse

In Mescal Wash on the desert slope of the San Gabriels, this mouse was one of the most abundant mammals and was the only rodent other than _Peromyscus maniculatus_ regularly trapped in the barren channels of washes. In Mescal Wash, at an alt.i.tude of 4000 feet, _eremicus_ occurred along with the chaparral-inhabiting _Peromyscus boylii_ and _Peromyscus californicus_. The two species last mentioned were a.s.sociated with the occasional large patches of manzanita, antelope brush, and other brush of the wash, whereas _eremicus_ was trapped in the rocky and sandy channels among scattered bushes of scale-broom. No specimens of _eremicus_ were taken on the juniper-clad benches adjacent to the wash.

_Specimens examined._--Los Angeles County: Mescal Wash, 4000 ft., 10 (4 PC).

=Peromyscus eremicus fraterculus= (Miller)

Cactus Mouse

This mouse was recorded from 1900 feet elevation, one mile south of the mouth of San Antonio Canyon, to 3200 feet elevation in Cajon Canyon.

This subspecies is characteristic of the sage belt and shows a strong preference for the rough rocky areas found in dry washes. Although in many areas the channels of the washes are immediately adjacent to sandy sagebrush-covered flats, _eremicus_ is not common in the latter areas.

Rocks seem to be essential to _eremicus_, for sandy areas in the sageland which were devoid of rocks yielded only an occasional specimen.

For example, 100 trap-nights in the main channel of San Antonio Wash yielded 23 _eremicus_ and only six other rodents; while in the sandy sage areas nearby 200 trap-nights yielded only one _eremicus_ and 32 other rodents.

In lower San Antonio Canyon _eremicus_ seemed restricted to the rocky canyon bottom, none having been trapped on the steep slopes nearby. This subspecies occurs commonly, however, on the adobe banks grown to white sage at the base of the foothills. There _eremicus_ occurred on common ground with _Perognathus fallax fallax_, and was often the only _Peromyscus_ taken.

This species may be restricted by temperature; washes above 4000 feet elevation, which seemed suitable were uninhabited by these mice.

On December 1, 1949, two females taken at the mouth of Palmer Canyon had well advanced embryos. A female trapped in San Antonio Canyon on September 19, 1951, was lactating. Juveniles were caught in the sage belt in October, 1951.

_Specimens examined._--Total, 6, distributed as follows: Los Angeles County: San Antonio Canyon, 2500 ft., 1; San Antonio Wash, 1800 ft., 5 (PC).

=Peromyscus californicus insignis= Rhoads

California Mouse

This mouse inhabits areas supporting chaparral on the coastal slope of the San Gabriels below 5000 feet. In the chaparral it is usually the most plentiful rodent, being dominant on slopes which have been burned over and on which greasewood chaparral has taken over. On one such slope at the head of Cow Canyon, at 4500 feet, this was the only rodent trapped, although an occasional wood rat house was noted. Trapping records gave the impression that this form was the most ubiquitous rodent in the entire chaparral belt. Nearly every trap line, even in such non-productive areas as oak woodland, took the California mouse; and in many areas, as in thick lilac brush, this mouse was by far the most abundant rodent. Specimens were taken on the damp ground next to San Antonio Creek, and in the riparian growth. In San Antonio Wash the California mouse was found in thickets of laurel sumac and lemonade berry, or other large shrubs, but were absent from most of the adjacent sageland. The one place where they were found away from heavy brush was on a series of barren adobe banks, near Palmer Canyon, clothed mostly with white sage. Here they found shelter in the unused burrows of kangaroo rats and ground squirrels.

The only place on the desert slope where this species was taken was in Mescal Wash. There it was taken occasionally near the large clumps of antelope-brush and manzanita which grew in the main channels of the wash.

Lactating females of this species were taken in October, 1949, and February, 1950. Two pregnant females were trapped on February 25, 1950, at the mouth of Palmer Canyon.

_Specimens examined._--Total 16, distributed as follows: Los Angeles County: Mescal Wash (4200 ft., 4; 4300 ft., 1; 4500 ft., 1), 6(2IM); San Antonio Canyon, 4500 ft., 1; San Antonio Canyon, 3000 ft., 5; mouth of Palmer Canyon, 1900 ft., 4 (PC).

=Peromyscus maniculatus gambeli= (Baird)

Deer Mouse

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 a.s.sociation, 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 s...o...b..sh, basin sagebrush, currant, and scattered conifers, and was found sparingly in the coniferous forests. Thus this species lives on contrasting soil types in a.s.sociation with many different vegetational a.s.semblages, 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 a.s.sociation 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 a.s.sociated 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 a.s.sociation.

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 a.s.signed 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 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 encompa.s.sing much of the chaparral and oak woodland a.s.sociations. It was the most common mammal in the oak woodland a.s.sociation 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 a.s.sociation 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 a.s.sociated with such desert forms as _Onychomys torridus pulcher_ and _Peromyscus eremicus eremicus_.