Transcriber's Note

The following changes have been made to the original text:

page 520: "Pinus Lambertiana" changed to "Pinus lambertiana"
page 531: "Virginia Opossom" changed to "Virginia Opossum"
page 551: "4600 ft. 3" changed to "4600 ft., 3"
page 555: "laural sumac" changed to "laurel sumac"
page 566: "concealed itelf" changed to "concealed itself"
page 582: "Oakshott, G. B." changed to "Oakeshott, G. B."

Instances of inconsistent hyphenation have been preserved.

In cases where tables were located in the middle of a paragraph, they have been moved to the next paragraph break. This may affect at what page number a table was originally located.

The list of University of Kansas publications was originally printed on the front and back covers. For this version of the text, the list has been combined and placed at the end of the text.

University of Kansas Publications
Museum of Natural History

Volume 7, No. 9, pp. 513-582, 4 pls., 1 fig. in text, 12 tables
November 15, 1954

Mammals of the San Gabriel Mountains
of California

BY
TERRY A. VAUGHAN

University of Kansas
Lawrence
1954

University of Kansas Publications, Museum of Natural History

Editors: E. Raymond Hall, Chairman, A. Byron Leonard,
Robert W. Wilson

Volume 7, No. 9, pp. 513-582, 4 pls., 1 fig. in text, 12 tables
Published November 15, 1954

University of Kansas
Lawrence, Kansas

PRINTED BY
FERD VOILAND, JR., STATE PRINTER
TOPEKA, KANSAS
1954

25-5184

MAMMALS OF THE SAN GABRIEL MOUNTAINS
OF CALIFORNIA

by
Terry A. Vaughan

CONTENTS

• PAGE
• [Introduction] [515]
• [Description of the Area] [516]
• [Biotic Provinces and Ecologic Associations] [518]
• • [Coastal Sage Scrub Association] [521]
  • [Southern Oak Woodland Association] [523]
  • [Chaparral Association] [524]
  • [Yellow Pine Forest Association] [526]
  • [Pinyon-juniper Woodland Association] [527]
  • [Sagebrush Scrub Association] [530]
  • [Joshua Tree Woodland Association] [530]
• [Accounts of Species] [531]
• [Literature Cited] [581]

Introduction

This paper presents the results of a study of the mammals of the San Gabriel Mountains of southern California, and supplements the more extensive reports on the biota of the San Bernardino Mountains by Grinnell (1908), on the fauna of the San Jacinto Range by Grinnell and Swarth (1913), and on the biota of the Santa Ana Mountains by Pequegnat (1951).

The primary objectives of my study were to determine the present mammalian fauna of the San Gabriel Mountains, to ascertain the geographic and ecologic range of each species, and to determine the systematic status of the mammals. In addition, certain life history observations have been recorded.

Field work was done in the north-south cross section of the mountains from San Gabriel Canyon on the west, to Cajon Wash on the east; and from the gently sloping alluvium at the Pacific base of the mountains at roughly 1000 feet elevation on the south, over the crest of the range to the border of the Mojave Desert at an elevation of 3500 feet on the north. Camps were established at many points in the area with the object of collecting the mammals of each association and each habitat. Field work was begun in the San Gabriels in November 1948, and was carried on intermittently until March 1952. I was unable to carry on field work in any summer.

For advice and assistance in various ways I am grateful to Drs. Willis E. Pequegnat, Walter P. Taylor, Henry S. Fitch, E. Raymond Hall, Mr. Steven M. Jacobs and my wife, Hazel A. Vaughan.

More than 350 mammals were prepared as study specimens; most of these are in the University of Kansas Museum of Natural History. Approximately a fifth of them are in the collection of the Department of Zoology at Pomona College, and a few are in the University of Illinois Museum of Natural History. No symbol is used to designate specimens in the University of Kansas Museum of Natural History. Specimens from the Department of Zoology of Pomona College and the University of Illinois Museum of Natural History are designated by PC and IM, respectively.

Fig. 1. Map of the San Gabriel Mountain area showing the positions of places mentioned in the text.

Description of the Area

The San Gabriel Mountains are approximately sixty-six miles long, and average twenty miles wide. The main axis of the range trends nearly east and west, and extends from longitude 117°25' to longitude 118°30'. The widest part of the range is bounded by latitude 34°7' and latitude 34°30'.

The San Gabriel Mountains connect the Sierra Nevada with the Peninsular Ranges of southern California and Baja California. On the west the San Gabriels are bordered by the Tehachapi Mountains, which stretch northeastward to meet the southern Sierra Nevada; to the east, beyond Cajon Pass, the San Bernardino Mountains extend eastward and then curve southward to the broad San Gorgonio Pass, from which the San Jacinto Range stretches southeastward to merge with the Peninsular Ranges.

The rocks comprising the major part of the San Gabriel Mountains probably were intruded in Late Jurassic times, with severe metamorphic activity taking place concurrently. A long period of erosion followed after which deposition took place during much of the Tertiary. Deformation and uplift beginning in Middle Miocene times resulted in the formation of east-west-trending faults along both sides of the range. By repeated movements along these faults the Late Jurassic crystalline rocks were lifted above late Tertiary and Quaternary sediments and elevated above the surrounding terrain. Continued uplifts in post-Pleistocene time together with erosion in Recent times have shaped the San Gabriel Mountains (Oakeshott, 1937).

The alluvial slopes at the coastal base of the range give way to the foothills at roughly 1800 feet elevation; whereas the Mojave Desert merges with the interior foothills at elevations near 4000 feet. The crest or drainage-divide of the range varies from 6000 to 8000 feet in elevation, and many peaks are more than 8000 feet high. San Antonio Peak, the highest peak of the range, rises to an altitude of 10,080 feet. The mountains are characteristically steep and the slopes are deeply carved by canyons, the larger of which have permanent streams. The abruptness of the Pacific slope is in many places impressive. The horizontal distance from the top of Cucamonga Peak, at an elevation of 8911 feet, to the base of the coastal foothills directly to the south, at 2250 feet, an elevational difference of 6661 feet, is only 3.8 miles. From the base of Evey Canyon, at 2250 feet, to an unnamed peak to the northwest with an elevation of 5420 feet, the horizontal distance is 2.1 miles. Because of the steep, rocky nature of many of the slopes and the lack of soil on them, vegetation may be sparse even at high elevations. There are few meadows in the mountains.

Because the San Gabriels stand approximately thirty miles from the Pacific Ocean and are a partial barrier to Pacific air masses sweeping inland, the desert side and the coastal side of the range differ climatically. The coastal slope receives much heavier precipitation than the desert slope. The precipitation, for 1951, of 25.36 inches recorded at the mouth of San Antonio Canyon on the Pacific slope contrasts with 7.17 inches recorded at Valyermo at the desert base. Nearly all of the precipitation comes in winter. The higher parts of the range, above approximately 5000 feet, receive much of their mid-winter precipitation in the form of snow. Snow often extends down the desert slope well into the Joshua Tree belt. When there are heavy winter rains the channels of the usually dry washes are filled with rushing, turbid water. There are striking differences in temperature between the two sides of the range and between the lower elevations of the mountains and the higher parts. For example, in December 1951, the mean temperature at the base of San Antonio Canyon (2225 feet) at the coastal foot of the range was 55.4°F, while at Llano (3764 feet) at the desert base it was 43.7°F. In this same year the December mean for Table Mountain (7500 feet), on the desert slope, was 33.4°F. The temperature means for July, 1951, at San Antonio Canyon, Llano, and Table Mountain, were 77.3°F, 82.1°F, and 69.2°F respectively. The weather records for 1951 were used for illustration because average temperature and average precipitation for many other years are lacking for most of the weather stations in the area. There is an important difference in the humidity on the two sides of the range, but actual data are not available. At certain times, especially in spring, fog banks moving in from the Pacific Ocean frequently blanket the coastal base of the mountains and the foothills. On such days the fog generally "burns off" in the morning, but may persist into the afternoon or throughout the day. Never in my experience has fog spilled over the main part of the range far onto the desert slope, although the fog may push through the lower passes to be dissipated quickly in the dry desert atmosphere. The obvious differences in the biota on the two sides of the range are probably due to the contrasting climates.

Biotic Provinces and Ecologic Associations

Because of the elevational extremes and attendant climatic contrasts in the San Gabriel Mountains, there is a rather wide range of environmental conditions. Four life-zones are represented: Lower Sonoran, Upper Sonoran, Transition, and Canadian. Within these zones certain ecologic communities can be recognized; these represent several biotic provinces. Table 1 shows the relationships between the environmental categories recognized by the writer in the San Gabriel Mountains. The biotic province and ecologic community system is that developed by Munz and Keck (1949), and the life-zone system is that of Merriam (1898).

Table 1.—Relations of the Major Environmental Categories of the San Gabriel Mountains.

The Californian Biotic Province dominates the biotic aspect of the coastal slope of the range. Thirty-nine out of the seventy-two mammals recorded from the San Gabriels are typical of this Province. The coastal sage-flats at the Pacific base of the mountains and the vast tracts of chaparral of the coastal slope are included in this Province.

Forming a hiatus between the Pacific and the desert slope is the Sierran Biotic Province consisting of coniferous forests on the crest of the range. The chipmunk (Eutamias speciosus speciosus) and the introduced black bear (Ursus americanus californiensis) are the only two mammals which can be considered typical of this area. On the higher peaks of the range, such as Mount San Antonio and Mount Baden Powell, the Canadian Life-zone is represented by certain boreal plants.

At scattered points along the crest of the range and on the desert slope, the Nevadan Biotic Province is represented by the sagebrush scrub association. No mammals can be considered typical of this region.

The Southern Desert Biotic Province occurs below 6000 feet elevation on the interior slope of the range, and markedly influences the mammal fauna of this slope. Twenty-one species of mammals are typical of this Province.

Scientific and Common Names of Plants Mentioned in This Report

Coastal Sage Scrub Association

Major Plants

Artemisia californica
Salvia apiana
Salvia mellifera
Eriogonum fasciculatum
Rhus integrifolia
Opuntia occidentalis
Haploppapus squarrosus

This association is restricted to the Pacific base of the range, is typical on the alluvium at the bases of the coastal foothills, and usually grades into the chaparral at about 1800 feet elevation. When seen from above, the rather level terrain of the association is broken sharply at the mouths of canyons by dry washes, and is limited below, to the south, by cultivated land. The coastal sagebrush is the most characteristic plant of this association, occurring in all undisturbed parts of the area.

There are several habitats within the coastal sage scrub association. These differ from one another chiefly on the basis of soil type. The soil of the rather level sageland in most places is rocky or gravelly, or, as adjacent to washes, it is finely sandy in texture, and supports the major plants of the association. Most of the eroded adobe banks at the bases of the foothills support these same plants, with white sage being the dominant species. Locally, as in damp hollows or cleared areas, there is grassland. Jumbles of boulders, sand, gravel, and steep cutbanks, are characteristic of the channels of dry washes, these areas supporting sparse vegetation. The fauna and flora of the washes are distinct from those of surrounding sage flats. Because they are included within the geographic limits of the coastal sage belt, however, the washes are discussed along with this association.

The abruptness with which one habitat gives way to another in this association causes sharp dividing lines between the local ranges of certain mammals. For example, in trap lines transecting dry washes and level sageland two assemblages of rodents were found. That part of the line amid the boulders and cutbanks of the wash took mostly Peromyscus eremicus fraterculus and Neotoma lepida intermedia, while Perognathus fallax fallax, Dipodomys agilis agilis, and Peromyscus maniculatus gambeli were taken in the adjacent sage flats. The steep adobe slopes of the foothills, which constitute the upper part of the coastal sage scrub association, are commonly inhabited by Peromyscus californicus insignis, which rarely occurs in the level tracts of sage a few yards away. Thus, this association is not homogeneous with regard to its rodent population; many of these species have local and discontinuous distributions.

The following list gives the results of about 500 trap nights (a trap night equals one trap set out for one night) in typical coastal sage-scrub association one-half mile southwest of the mouth of San Antonio Canyon, at 1700 feet elevation.

Table 2.—Yield of 500 Trap-nights in the Coastal Sage Scrub Association.

The list below indicates the catch in 200 trap nights in San Antonio Wash, at 1700 feet elevation and within the realm of the coastal sage; all of the traps were set in rocky and sandy main channels of the wash.

Table 3.—Yield of 200 Trap-nights in San Antonio Wash.

The prickly-pear cactus is of obvious importance to certain mammals of the coastal sage belt. This cactus is most common in disturbed areas such as sandy flats bordering washes, eroded adobe banks, and land once cleared by man. In these areas it is often the dominant plant with respect to area covered, usually growing in dense patches each covering approximately 150 square feet. It provides substitute nesting sites for Neotoma lepida in areas devoid of rock piles, and is probably the major factor governing the distribution of this wood rat in the sageland. Cottontails and brush rabbits use prickly-pear cactus extensively as refuge. Their forms and short burrows can be seen beneath many of the clumps of cactus.

This cactus serves as food for many mammals at least in the fruiting period in the fall. Usually only the fruit is eaten, but some pads are chewed by rabbits. The fruit or seeds of this plant are eaten by striped skunks, gray foxes, coyotes, pocket mice, kangaroo rats, wood rats, and probably white-footed mice.

The coyote is the dominant carnivore of the coastal sage flats. Many individuals spend the day in the adjacent chaparral-covered foothills and travel down into the flats at night to forage.

Southern Oak Woodland Association

Major Plants

Alnus rhombifolia
Quercus agrifolia
Ribes indecorum
Rhus integrifolia
Rhus ovata
Rhus trilobata

This association is limited to the Pacific slope of the mountain range, occurs in the mouths of canyons and on the floors of canyons, and extends up the larger canyons to 4000 feet elevation or higher. In a few areas on the flats at the coastal base of the range the oaks replace the coastal sage.

The large oaks forming an overhead canopy and the lack of much undergrowth give the oak woodland a shaded parklike appearance. Few brushy or herbaceous plants grow in the mull-laden soil beneath the oaks. Some grasses, however, are present locally.

Two habitats are found in the oak woodland: the pure oak woodland and the riparian. Much of the oak woodland is in canyons and therefore near streams or seepages. The larger streams have bordering growths of alders, willows, and blackberries, inhabited by meadow mice and shrews that are normally absent from the adjacent oak woodland. Neotoma fuscipes macrotis and Peromyscus californicus insignis are commonly found in the riparian habitat, and Peromyscus boylii probably reaches peak abundance in the stream-side thickets and tangles of plant debris.

The rather open floor of the oak woodland is relatively devoid of mammal life. Peromyscus californicus and Peromyscus boylii, the only ground-dwelling rodents commonly found here, usually are taken near the limited areas of brushy growth, or the shelter afforded by logs and fallen branches. The paucity of shelter for small mammals seems to be an important factor limiting rodent populations in the oak woodland.

In the foothills of the San Gabriels the gray squirrel is restricted to the oak woodland, even though this association may be represented by only a narrow strip of canyon bottom oak trees. The presence or absence of "bridges" of oak woodland between mountains which are centers of gray squirrel populations and nearby ranges has probably been a major factor influencing the present geographic distribution of this animal.

The raccoon is the most abundant carnivore of the oak woodland, being especially common in the riparian habitat.

Chaparral Association

Major Plants

Adenostoma fasciculatum
Rhamnus crocea
Quercus dumosa
Cercocarpus betuloides
Yucca Whipplei
Prunus ilicifolia
Ceanothus sp.
Arctostaphylos sp.
Umbellularia californica

This association is characteristic of the Pacific slope of the San Gabriels and extends from roughly 2000 feet elevation to 5000 or 6000 feet elevation. The ecotone between the chaparral and yellow pine forest associations covers a broad elevational belt, with chaparral following dry slopes up into coniferous forests, and conifers extending down north slopes surrounded by chaparral.

The chaparral association is characterized by tracts of dense brushy plants. These plants are from three to ten feet tall, their interlacing branches often forming nearly impenetrable thickets. Typically little herbaceous growth is present beneath the chaparral, the ground being covered with varying amounts of mull.

The effects of fire, slope, exposure, and elevation, make the chaparral association extremely varied with regard to habitats or plant formations. There are nearly pure stands of greasewood on the lower arid slopes; scrub oak, sumac, and lilac clothe less dry exposures; scrub oak and bay trees occur commonly amid granite talus; and locally groves of bigcone-spruce are found. Because of the many habitats present, and the difficulty of collecting in the chaparral, less was learned of the ecology of the mammals in this association than of those occurring elsewhere. The distribution of several chaparral-inhabiting mammals seems to be influenced by the distribution of locally characteristic plants, for example oak and bay woodland, or greasewood chaparral.

Several habitats within the chaparral community support few species of mammals and few individuals. Possibly the compact, rocky nature of the soil limits burrowing rodents, and the lack of herbaceous growth limits the food supply. Steep rocky slopes in San Antonio Canyon grown to mountain-mahogany and scrub oak were sparsely populated by Peromyscus boylii rowleyi, Peromyscus californicus insignis, and Neotoma fuscipes macrotis. Fifty traps set on such a slope for one night caught only three Peromyscus. Traps set in tracts of greasewood brush on dry south slopes at the head of Cow Canyon produced only California mice, Peromyscus californicus insignis Rhoads.

Following is a list of the mammals taken in the course of approximately 600 trap nights in the lower parts of the chaparral belt. All of the traps were set on slopes in San Antonio Canyon below 4000 feet elevation. The list gives a general indication of the relative numbers of rodents inhabiting one chaparral habitat: the arid greasewood-covered south slopes of the lower chaparral belt.

Table 4.—Yield of 600 Trap-nights in Greasewood Chaparral.

Heteromyids are evidently absent from the upper parts of the chaparral association, but cricetid rodents are common there beneath heavy clumps of lilac and in the talus beneath oaks and bay trees. The following list gives the mammals taken in the course of about 200 trap nights in the granite talus one half mile northwest of the mouth of Icehouse Canyon, at 5200 feet elevation.

Table 5.—Yield of 200 Trap-nights in the Upper Part of the Chaparral Association.

The gray fox is the dominant carnivore of the chaparral association and forages widely in all habitats.

Yellow Pine Forest Association

Major Plants

Pinus ponderosa
P. lambertiana
Libocedrus decurrens
Abies concolor
Quercus Kelloggii
Ribes nevadense
Ribes Roezlii
Arctostaphylos sp.
Ceanothus cordulatus

The crest of the range, from the upper limit of the chaparral association at roughly 6000 feet to the limited areas of boreal flora above 8500 feet elevation, is covered by yellow pine forests. On the desert slope of the range the coniferous forests which extend down to about 6000 feet represent the best development of this association, while the coniferous forests on the coastal side of the drainage divide are often more or less diluted by chaparral elements. For example, yellow pines on the Pacific face of Blue Ridge at 7000 feet elevation often grow in association with scrub oak and mountain-mahogany.

Few mammals are resident in the typical yellow pine forest as characterized by dense coniferous timber and little herbaceous or brushy growth. Here most of the species recorded actually find optimal conditions in an adjacent habitat. The forest probably harbors surplus individuals from adjacent preferred habitats, or, as in the case of chipmunks and ground squirrels, the forest often serves as forage ground while nearby brushy areas are utilized for breeding and shelter. The abundance of birds in the timber contrasts strikingly with the paucity of mammals there. The lack of a seed-producing understory, and the open duff-covered stretches of ground on which rodents would be extremely vulnerable to predation, probably in part account for the scarcity of rodents.

Within the general area encompassed by the yellow pine forest there are two major habitats, namely coniferous forest and chaparral. The species of plants comprising the chaparral of the Transition Life-zone are different from those comprising the chaparral of the Upper Sonoran Life-zone on the Pacific slope. In the chaparral of the Transition Life-zone, basin sagebrush and snowbrush grow in extensive patches in clearings in the timber. Dense thickets of choke cherry cover many damp hollows, and these thickets harbor the houses of Neotoma fuscipes. The food and shelter afforded by these chaparral areas importantly influence the local distribution of rodents: for example, Dipodomys agilis and Perognathus californicus in the yellow pine area are found only in association with chaparral, being completely absent from wooded areas.

The severe winter weather in this association must force many of the mammals into periods of inactivity. Probably during the long periods in the winter when snow covers the ground the heteromyids and sciurids remain below ground.

Pinyon-Juniper Woodland Association

Major Plants

Pinus monophylla
Juniperus californica
Quercus dumosa var. turbinella
Purshia glandulosa
Fremontia californica
Cercocarpus ledifolius
Yucca Whipplei

In the San Gabriel Mountains this association is limited to the desert slope and reaches its lower limit at the bases of the foothills and extends up to the lower edge of the yellow pine forests. The altitudinal extent of the pinyon-juniper association is from roughly 4000 to 6000 feet elevation.

Several habitats are evident within the pinyon-juniper belt. On north slopes in the upper part of this association, scattered stands of pinyon pines are found with dense patches of scrub oak intervening, while on other such slopes a dense chaparral is present, consisting primarily of scrub oak, mountain-mahogany, and California slippery-elm. In this type of chaparral several hundred trap nights yielded only two rodent species: Neotoma fuscipes simplex and Peromyscus truei montipinoris. There are few pinyons on the south slopes, especially in the lower parts of the association; many of these slopes are clothed with an open growth of manzanita and yucca, while northern exposures there support mostly scrub oak. Many of the flats of the pinyon belt are grown to basin sagebrush.

Following is a list of the mammals taken in about 400 trap nights at one locality in the pinyon-juniper association. The area supported a mixed growth of pinyon, scrub oak, mountain-mahogany, and antelope-brush, together with smaller brushy plants, and was at the head of Grandview Canyon, at an altitude of roughly 5000 feet.

Table 6.—Yield of 400 Trap-nights in the Pinyon-juniper Association.

Although Munz and Keck (1949:101) considered the pinyon-juniper belt as one association, on the desert slope of the San Gabriels pinyons and junipers do not generally grow on common ground; but rather the juniper belt represents a well defined habitat occurring between the pinyon covered slopes and the flats that support Joshua trees. Because the mammalian populations of the pinyon belt and the juniper belt are somewhat different, the mammals of these areas are most conveniently taken up separately.

In the juniper belt the juniper tree is of marked ecologic significance; the distribution of Peromyscus truei and Neotoma fuscipes is determined here by the presence of junipers. At certain times of year the fruit of this plant is eaten by coyotes, kangaroo rats, and wood rats.

The list below indicates the results of approximately 500 trap nights in the juniper belt near Mescal Canyon, between 4000 and 5000 feet elevation.

Table 7.—Yield of 500 Trap-nights in the Juniper Belt.

The biota of the washes that cut through the juniper belt in and below many of the larger canyons differs from that of the surrounding juniper-clad benches. Because the washes are in the same geographic area as the juniper belt they are discussed together. These washes on desert slopes are densely populated by rodents derived from adjacent areas, and support vegetation typical of higher floral belts in association with xerophytic, typically desert, species. In a sense, the washes serve to mix up the mammals of adjacent areas. For example, Onychomys torridus pulcher and Peromyscus eremicus eremicus, which are mammals typical of the desert, were found in Mescal Wash above their usual desert range; and Peromyscus californicus insignis and Peromyscus boylii rowleyi, which are chaparral inhabiting mammals, were found in the wash far removed from their chaparral environment. Washes are evidently effective agents in facilitating the dispersal of certain species of mammals. It is easy to envision a species crossing hostile habitats via dry washes to invade suitable niches in an area which is geographically and ecologically isolated from the original home of the species. Approximately 500 trap nights in Mescal Wash, at 4100 feet elevation, in the lower edge of the juniper belt, yielded the following mammals:

Table 8.—Yield of 500 Trap-nights in Mescal Wash (Desert Slope).

Dipodomys panamintinus mohavensis, Neotoma fuscipes simplex, and Peromyscus truei montipinoris are probably the most characteristic mammals of the pinyon-juniper association.

Sagebrush Scrub Association

Major Plants

Bromus sp.
Artemisia tridentata
Chrysothamnus nauseosus
Purshia glandulosa

This association is found on only the crest and desert slope of the range between 5000 and 8000 feet elevation. There it characteristically occupies flats and clearings in the yellow pine forest and pinyon-juniper woodland. The dominant plant of the association is basin sagebrush, and in many places this plant forms mixed growths with snowbrush and Haplopappus. The low brush of this association is formed by closely spaced bushes with grasses growing between.

Because of its limited occurrence in the San Gabriel Mountains, this association there has relatively little effect on mammalian distribution. Locally, nevertheless, the presence of this association governs the distribution of certain mammals. For example, on Blue Ridge, islands of sagebrush amid the conifers provide suitable habitat for Dipodomys agilis perplexus and Perognathus californicus bernardinus; and in Swarthout Valley D. a. perplexus, Reithrodontomys megalotis longicaudus, and Lepus californicus deserticola are seemingly restricted to the sagebrush flats.

Joshua Tree Woodland Association

Major Plants

Yucca brevifolia
Lycium Andersonii
Eriogonum fasciculatum
Tetradymia spinosa
Ephedra sp.
Larrea divaricata

This association is on the piedmont that dips toward the Mojave Desert from the interior base of the San Gabriels. The widely spaced Joshua trees with low bushes between, and the dry washes breaking the level terrain below the mouths of canyons are typical of this area. Field work was extended no farther down into the desert than about the 3500 foot level, where this association was still dominant.

Although the vegetation of this area is scattered and sparse, presenting a barren and sterile aspect, the area supports a rather high population of rodents. The soil at the bases of many large box-thorn- and creosote-bushes is perforated by burrow systems of Dipodomys panamintinus or Dipodomys merriami, and those burrows abandoned by kangaroo rats are used as retreats by Onychomys torridus and Peromyscus maniculatus. The mammals of this association are all characteristic of the fauna of the Mojave Desert, with the ranges of such species as the coyote and jack rabbit extending well up the desert slope of the mountains.

The mammals listed below were taken in 1948 in roughly 400 trap nights in the Joshua belt, at an elevation of 3500 feet, one mile below the mouth of Graham Canyon.

Table 9.—Yield of 400 Trap-nights in the Joshua Tree Belt.

Populations of Dipodomys merriami and D. panamintinus fluctuate widely, possibly in response to weather cycles. In November of 1948 trapping in the Joshua belt showed that panamintinus outnumbered merriami approximately three to one, whereas in December of 1951, after a succession of unusually dry years, merriami was the more numerous. Further, merriami occurred in the lower parts of the juniper belt in 1951 where in 1948 it seemed to be absent.

Dipodomys merriami merriami and Onychomys torridus pulcher are diagnostic of the Joshua tree woodland association in the San Gabriel Mountains area, since few individuals of either species occur outside of this association.

PLATE 1

Fig. 1. View of typical coastal sage scrub association, showing in foreground white sage, and coastal sagebrush. The adobe banks beyond are grown mainly to white sage. Small mammals are abundant in this association, with Dipodomys agilis, Perognathus fallax, and Sylvilagus audubonii being characteristic of the area. Photo March 25, 1952, at mouth of San Antonio Canyon, 1800 feet elevation.

Fig. 2. View of a main channel in San Antonio Wash on Pacific slope. The wash is a distinct habitat in the coastal sage scrub association, and is the preferred habitat of Peromyscus eremicus fraterculus and Neotoma lepida intermedia. These rodents find shelter in the piles of boulders. Photo February 2, 1952, in San Antonio Wash, at 1700 feet elevation.

PLATE 2

Fig. 1. Southern oak woodland association. The open leaf-strewn floor of the woodland lacks shelter for ground-dwelling rodents and the population of rodents is small. Peromyscus boylii rowleyi is the commonest rodent. Photo March 10, 1952, in Evey Canyon, 2700 feet elevation.

Fig. 2. Yellow pine forest association, composed largely of yellow pines, white fir, and black oak. Photo April 27, 1952, at Big Pines, 6800 ft. elevation.

PLATE 3

Fig. 1. View of the sagebrush scrub association showing a nearly pure stand of basin sagebrush. Dipodomys agilis perplexus and Reithrodontomys megalotis longicaudus occur in this association, and Peromyscus truei montipinoris is present where this association merges with the pinyon-juniper association. Photo April 27, 1952, in Swarthout Valley, 6200 feet elevation.

Fig. 2. View of a pinyon pine woodland. This habitat constitutes the upper part of the pinyon-juniper association, and is the habitat of Neotoma fuscipes simplex, Peromyscus truei montipinoris, and Eutamias merriami merriami. Photo April 27, 1952, in Sheep Creek Canyon, 5500 feet elevation.

PLATE 4

Fig. 1. View of the juniper belt. This habitat forms the lower part of the pinyon-juniper association. Perognathus fallax pallidus, Dipodomys panamintinus mohavensis, and Peromyscus truei montipinoris are typical of this area. Photo April 27, 1952, at Desert Springs, 4300 feet elevation.

Fig. 2. Joshua tree woodland association. The characteristic mammals are Dipodomys panamintinus mohavensis, D. merriami merriami, and Onychomys torridus pulcher. Photo January 4, 1952, 6 miles east and 2 miles south Llano, 3600 feet elevation.

Accounts of Species

Family DIDELPHIDAE

Didelphis marsupialis virginiana Kerr

Virginia Opossum

The opossum is common in and near small towns and cultivated areas at the Pacific base of the mountain range and does not thrive away from human habitation; extensive trapping in the coastal sage and chaparral belts produced no specimens except immediately adjacent to citrus groves. Pequegnat (1951:47) mentions that opossums in the Santa Ana Mountains of southern California are in the lower parts of the larger canyons, especially near human habitation.

Specimens examined.—Los Angeles County: Claremont, 1600 ft., 2 (PC).

Family TALPIDAE

Scapanus latimanus occultus Grinnell and Swarth

California Mole

Workings of moles were found on the Pacific slope of the mountains from 1600 feet at Claremont up to 7500 feet on Blue Ridge, and on the Pacific slope beneath basin sagebrush in Cajon Canyon one mile from desert slope Joshua-tree flats, but not on the desert slope, although moles probably occur on that slope in some of the places where there is suitable habitat.

Near Camp Baldy in the sandy soil beneath groves of alders moles seemed to be especially abundant. Although common on the coastal face of the range, moles shunned compact, dry, or rocky soils. In the greasewood chaparral one-half mile west of the mouth of Palmer Canyon, where the soil was hard and rocky, mole tunnels were in soft soil that had accumulated at the edge of a fire road beneath a steep road cut. The assumption is that this accumulation contained insects attractive, as food, to the moles.

Specimens examined, 2: Los Angeles County: Camp Baldy, 4200 ft., 1(PC); Claremont, 1600 ft., 1(PC).

Family SORICIDAE

Sorex obscurus parvidens Jackson

Dusky Shrew

Jackson (1928:124) recorded a specimen from Camp Baldy, 4200 feet, San Antonio Canyon.

Sorex ornatus ornatus Merriam

Ornate Shrew

Both of my specimens were taken amid riparian growth on the Pacific slope of the range.

Specimens examined, 2: Los Angeles County: San Antonio Canyon, 3500 ft., 1; Cobal Canyon, 5 mi. N Claremont, 1800 ft., 1 (PC).

Notiosorex crawfordi crawfordi (Coues)

Gray Shrew

One was taken in 1946 beneath a woodpile on the campus of Norton School, two miles northeast of Claremont, and examined by Dr. W. E. Pequegnat.

Family VESPERTILIONIDAE

Myotis yumanensis sociabilis H. W. Grinnell

Yuma Myotis

A female was taken in lower San Antonio Canyon, 2800 feet elevation, on September 27, 1951.

Myotis evotis evotis (J. A. Allen)

Long-eared Myotis

This species was observed and collected at several stations ranging from 2800 feet elevation in San Antonio Canyon, to Blue Ridge at 8200 feet, and down the desert slope to 6000 feet at Jackson Lake. This distribution encompasses most of the chaparral and yellow pine forest associations. Within these areas, however, this bat shows marked habitat preferences.

Woodland habitats seem to be preferred by evotis. At several ponds in lower San Antonio Canyon this bat was observed repeatedly as it foraged over the water and coursed low between rows of alders and Baccharis. At Blue Ridge in September, 1951, these bats foraged approximately six feet above the ground beneath the canopy of coniferous foliage and between the trunks of the trees.

Most of the bats were taken by stretching fine wires above the surface of a pond as outlined by Borell (1937:478). Collecting was generally carried on until at least 11:00 p. m., and the time at which each bat was taken at the pond was recorded, thereby making possible a rough estimate of the pre-midnight forage period of each bat commonly collected at the ponds. Usually bats taken at the start of their supposed forage period had empty or nearly empty stomachs, whereas those taken towards the end of their forage period had full or nearly full stomachs. M. evotis usually first appeared just at dark, well after the pipistrelles and California myotis had begun foraging. The forage period of evotis seemed to begin approximately 30 minutes after sunset and to end approximately two and one-quarter hours later.

Individuals of this species were taken from May 4, to October 14, 1951. A female taken on May 19, 1951, in San Antonio Canyon, carried one minute embryo, and one taken in the same locality on June 8, had one embryo four millimeters in length.

Specimens examined.—Total, 12, distributed as follows: Los Angeles County: San Antonio Canyon, 2800 ft., 11; Claremont, 1100 ft., 1 (P.C.).

Myotis volans interior Miller

Interior Long-legged Bat

Although seldom found to be plentiful, this bat was recorded from many points on both the coastal and desert slopes of the mountains. Specimens were taken in the chaparral association in San Antonio Canyon, near Jackson Lake among yellow pines, and in Mescal Canyon at the upper limit of the Joshua tree woodland. Bats, probably volans, were noted over sage flats at 8000 feet elevation on Blue Ridge. The only place where these bats appeared to be numerous was Jackson Lake on the interior slope; there, on September 19, 1951, volans appeared with the pipistrelles, and was the most common bat before dark.

An individual of this species taken on October 28, 1951, in a short mine-shaft in the pinyon belt at the head of Grandview Canyon was slow in its movements and felt as cold as the walls of the tunnel. It was late afternoon and the temperature outside the cave was below 40°F. The floor of the tunnel was covered with the hind wings of large moths of the genus Catocala; volans probably hung in the cave while eating them.

The series of volans from the San Gabriels shows that the two color phases of this bat both occur in the area. Two specimens from Jackson Lake contrast sharply with the rest of the series in their dark coloration. Benson (1949:50) states that color variation in a series of volans from a given locality may be striking.

This bat was collected in San Antonio Canyon from 50 minutes after sundown to two hours and 40 minutes after sundown. In this area these bats did not visit the ponds in large numbers as they seemed to do on the desert slope.

A female taken on May 29, 1951, contained one embryo nearly at term.

Specimens examined.—Total, 9, distributed as follows: Los Angeles County: Mescal Canyon, 8 mi. E and 5 mi. S Llano, 4900 ft., 1; 3 mi. W Big Pines, Swarthout Valley, 6000 ft., 3; San Antonio Canyon, 2800 ft., 5.

Myotis californicus californicus (Audubon and Bachman)

California Myotis

On the Pacific face of the mountain range this bat was recorded commonly below approximately 5000 feet elevation, where it seemed to be most common in the oak woodland of canyons. On the desert slope it was collected at Jackson Lake in yellow pine woodland, in Mescal Canyon in the juniper belt, and bats presumably of this species were observed at several points in the pinyon-juniper woodland.

Individuals of this species were often observed foraging from five to ten feet above the ground around the alders and Baccharis near San Antonio Creek, but they did not fly so low or so near the vegetation as did Myotis evotis. Here they were taken from 18 minutes to 55 minutes after sunset; this indicates an early and short forage period.

This bat may be active even in winter. On February 8, 1952, in lower San Antonio Canyon, a bat, probably of this species, was noted foraging; and collecting in early November, 1951, yielded specimens.

On May 22, 1951, a female obtained in San Antonio Canyon had one five-millimeter embryo, and subsequently all the females examined had embryos until June 12, when collecting was discontinued.

Specimens examined.—Total, 16, distributed as follows: Los Angeles County: Mescal Canyon, 4800 ft., 2; Jackson Lake, 6000 ft., 1 (PC); San Antonio Canyon, 3900 ft., 1; San Antonio Canyon, 2800 ft., 12.

Pipistrellus hesperus merriami (Dobson)

Western Pipistrelle

This is the most obvious if not the most common bat of the lower coastal slopes of the San Gabriels. In the spring and fall of 1951 individuals were noted from 1700 feet in the coastal sage scrub association to the white fir forests on Blue Ridge at 8200 feet elevation and were commonest in the rocky canyons of the lower Pacific slope below 4000 feet, and usually foraged near the steep canyon sides high above the canyon bottoms.

Pipistrelles were generally the first bats to appear in the evening, although the times of their appearance were irregular. In April and May, in lower San Antonio Canyon, they appeared from 28 minutes before sunset to 30 minutes after sunset, with the average time of appearance eight and one-half minutes after sunset. Like Myotis californicus this pipistrelle seemed to have a short and early foraging period. No pipistrelles were recorded at ponds later than one hour and five minutes after sunset, and usually they were not seen later than 40 minutes after sunset. Most of the specimens taken later than one half hour after sunset had full stomachs. More than 50 pipistrelles were captured at the ponds in San Antonio Canyon; six were kept for specimens. This species is probably present in the area throughout the winter. Pipistrelles were active in early April in Evey Canyon, were observed in early November in San Antonio Canyon, and on January 26, 1952, an individual was noted foraging near the mouth of Palmer Canyon. They are probably not active in winter on the colder desert slope of the mountains.

Pipistrelles often foraged in loose flocks of about half a dozen individuals. On many occasions these groups were first seen foraging high up above the canyon bottom, then, as it grew darker, they descended and foraged within 50 or 100 feet of the floor of the canyon. Immediately before dark these groups seemed to have forage beats; one minute several pipistrelles would be overhead, and the next minute none would be in sight.

A female taken in San Antonio Canyon on June 8, 1951, contained two five-millimeter embryos.

Specimens examined.—Total, 6, distributed as follows: Los Angeles County: San Antonio Canyon, 2800 ft., 5; Evey Canyon, 2400 ft., 1.

Pipistrellus hesperus hesperus (H. Allen)

Western Pipistrelle

This species was common in the spring and autumn of 1951 from the lower edge of the yellow pine forest down into the belt of Joshua trees. In early April on the desert slope at 4800 feet in Mescal Canyon, pipistrelles foraged on evenings when it was windy but not cold. On cold evenings (when the temperature was below roughly 45°F) none was seen. On windy nights the pipistrelles often forsook their usual high forage habits and foraged 15 feet or so above the ground where the vegetation and outcrops of rock broke the force of the wind. In 1951 no pipistrelles were noted on the desert slope later than October 15.

Specimens examined.—Los Angeles County: Mescal Canyon, 4800 ft., 4.

Eptesicus fuscus bernardinus Rhoads

Big Brown Bat

This bat was on the coastal slope from the sage scrub association at 1100 feet, up to 8000 feet on Blue Ridge, and on the desert slope down to the upper edge of the Joshua tree belt at 4800 feet in Mescal Canyon. It was the most common bat at the ponds in San Antonio Canyon in May and June of 1951, but in September and October of the same year none was obtained there.

On the Pacific slope of the San Gabriels the big brown bats segregate according to sex in the spring, the males occupying the foothills and mountains and the females the level valley floor at the coastal base of the range. Of 70 big brown bats captured in May and June of 1951, at the ponds in San Antonio Canyon, only one was a female. A large colony of more than 200 individuals in a barn near Covina, in the citrus belt, was composed of only females.

Times of capture of this bat at the ponds in San Antonio Canyon ranged from ten minutes after sunset to two hours and thirty minutes after sunset. Generally these bats came to the ponds in groups of several individuals, and often more than a dozen were captured in the course of an evening's collecting.

Specimens examined.—Total, 7, distributed as follows: Los Angeles County: Mescal Canyon, 4800 ft., 1; San Antonio Canyon, 2800 ft., 2; Covina, 1100 ft., 4 (2PC).

Lasiurus borealis teleotis (H. Allen)

Red Bat

One female was taken on September 30, 1951, in San Antonio Canyon, at 2800 feet elevation. The descriptions which the citrus growers of the Claremont and Glendora vicinity give of the bats they find occasionally hanging in their citrus trees accurately describe this species. Its seasonal occurrence there is unknown.

Lasiurus cinereus cinereus (Pasilot de Beauvois)

Hoary Bat

Specimens were collected in spring in 1951 at elevations of 2800 and 3200 feet in San Antonio Canyon, on the coastal slope, and in Mescal Canyon at 4900 feet, on the desert slope. Large, fast flying bats, probably of this species, were seen at Jackson Lake, 6000 feet elevation, on October 15, 1951.

Hoary bats are present in the San Gabriels in the fall, winter, and spring. In 1951 the last spring specimen was taken on June 11, in Mescal Canyon; then collecting was discontinued until late September when the first hoary bat was taken on the thirtieth of that month. From this date on into the winter hoary bats were recorded regularly. They seemed to be as common in early June as in most of April and May; possibly some remain in the San Gabriels throughout the summer.

In spring these bats seem to segregate by sex; of twelve kept as specimens and at least an equal number captured and released only one was a female. All were captured above 2800 feet.

Hoary bats seem to have a long pre-midnight forage period, having been captured at ponds from 21 minutes after sunset, to three hours and 26 minutes after sunset. Generally those taken early had empty stomachs and those taken later had full stomachs. On the night of May 24, 1951, a hoary bat captured two hours and five minutes after sunset had only a partially full stomach.

On May 25, 1951, an unusual concentration of hoary bats was observed at a pond at about 3200 feet elevation, in San Antonio Canyon (Vaughan, 1953). The day had been clear and warm, one of the first summerlike days of spring. Beginning at 30 minutes after sundown hoary bats were collected until two hours and 35 minutes after sundown; in this period 22 were caught and at least as many more observed. Many were released after being examined, whereupon they hung on the foliage of nearby alders to rest and dry themselves. This concentration of hoary bats may have been due to a sudden beginning of migration with a resultant concentration of bats at certain altitudinal belts. The warm weather might have set off the migration. On evenings that followed subsequent hot days no such concentration of hoary bats was seen. B. P. Bole (Hall 1946:156) observed a concentration of hoary bats on August 28, 1932, in Esmeralda County, Nevada.

Several captive Myotis californicus in a jar next to a pond in San Antonio Canyon set up a squeaking which seemed to attract a hoary bat. Repeatedly the large bat swooped over the jar.

Specimens examined.—Total, 12, distributed as follows: Los Angeles County: Mescal Canyon, 4900 ft., 2; San Antonio Canyon, 3200 ft., 2; San Antonio Canyon, 2800 ft., 8.

Antrozous pallidus pacificus Merriam

Pallid Bat

The pallid bat is probably the most common and characteristic bat of the citrus belt at the Pacific base of the mountains. Only once, on May 4, 1951, was this bat taken in the mountains. On that night two individuals were collected at 2800 feet in San Antonio Canyon. All of the other specimens and observations were from colonies in old barns and outbuildings in the citrus belt where these bats are found in spring, summer, and fall.

The impression gained by examining many mixed colonies of Antrozous and Tadarida was that the former greatly outnumbered the latter. For example, a small colony of bats in an old barn near San Dimas Wash consisted of about thirty pallid bats and five freetails.

Large numbers of wings of moths of the family Sphingidae, and legs and parts of the heads of Jerusalem crickets (Stenopelmatus fuscus) were beneath an Antrozous night-roosting place in a barn near Upland.

Pallid bats were collected in 1951, from April 16 to October 17 but probably were active in the area into November.

Each of two pregnant females taken two miles northeast of San Dimas on April 20, 1951, carried two embryos 4 millimeters long.

Specimens examined.—Total, 6, distributed as follows: Los Angeles County: 2 mi. NE San Dimas, 1200 ft., 2 (1PC); Ontario, 1100 ft., 4 (3PC).

Family MOLOSSIDAE

Tadarida mexicana (Saussure)

Mexican Free-tailed Bat

This bat, regularly met with in the citrus belt at the coastal base of the range, occurred in small numbers with colonies of Antrozous, and was once found with a colony of Eptesicus near Covina. None of the females taken in April 1951 was pregnant.

Specimens examined.—Los Angeles County: 2 mi. NE San Dimas, 1200 ft., 4.

Eumops perotis californicus (Merriam)

Mastiff Bat

H. W. Grinnell (1918:373) mentioned individuals collected at Sierra Madre (at the coastal base of the San Gabriels west of the study area), and Sanborn (1932:351) reported specimens from Covina and Azusa. Probably this bat occurs locally all along the coastal base of the range.

Family LEPORIDAE

Lepus californicus bennettii Gray

California Jack Rabbit

This species was found in the coastal sage belt from Cajon Wash west to San Gabriel Canyon and was most plentiful in thin stands of sagebrush, and in and around citrus groves. Because of their preference for semi-open country, jack rabbits are absent from much of the coastal belt of sagebrush where the brush is fairly continuous, and they never were observed in the chaparral association.

Coyotes catch many jack rabbits and regularly forage around the foothill borders of the citrus groves for cottontails and jack rabbits.

A female examined on February 19, 1951, was pregnant, and one taken on March 15, 1951, carried three small embryos.

Specimens examined.—San Bernardino County: 2 mi. NW Upland, 1600 ft., 3 (PC).

Lepus californicus deserticola Mearns

California Jack Rabbit

There was sign of jack rabbits along the desert slope of the San Gabriels up to about 6700 feet, one-half mile west of Big Pines. They were fairly common in the Joshua tree belt, occurred less commonly in the juniper belt, and were present locally in small numbers in the pinyon-juniper association.

The population seemed to be at a low ebb from 1948 to 1952, when field work was done on the desert slope. I often hiked for an hour or more on the desert or juniper-covered benches without seeing a jack rabbit. The species was commoner in washes where as many as eleven were noted in two hours' hiking.

In December, 1951, below Graham Canyon, the leaves on large areas of many nearly recumbent Joshua trees had been gnawed down to their bases, and jack rabbit feces covered the ground next to these gnawings. Probably the Joshua tree is an emergency food used by the rabbits only when other food is scarce.

In years when the population of jack rabbits is not low they serve as a major food for coyotes. In the Joshua tree belt below Mescal Canyon, jack rabbit remains were fairly common in coyote feces, and tracks repeatedly showed where some coyote had pursued a jack rabbit for a short distance. A large male bobcat trapped in the juniper belt in Graham Canyon had deer hair and jack rabbit remains in its stomach.

Specimens examined.—Total, 7, distributed as follows: Los Angeles County: 6 mi. E and 1 mi. S Llano, 3500 ft., 4; Mescal Canyon, 4800 ft., 3.

Sylvilagus audubonii sanctidiegi (Miller)

Audubon Cottontail

Cottontails are common in the coastal sage scrub association and in and around citrus groves, but generally penetrate the mountains no farther than the lower limit of the chaparral association. They are everywhere on coastal alluvial slopes, except in the barren washes, and prefer patches of prickly-pear and often are loathe to leave its protection. After completely destroying a large patch of prickly-pear in the course of examining a wood rat house in the center of the cactus, I found hiding, in the main nest chamber of the house, a cottontail that dashed from its hiding place only when poked forceably with the handle of a hoe.

Cottontails are seldom above the sage belt in the chaparral associations, although along firebreaks and roads they occasionally occur there. Habitually cottontails escape predators in partly open terrain offering retreats such as low, thick brush, rock piles, and cactus patches; but on open ground beneath dense chaparral, cottontails may be vulnerable to predation.

Examinations of feces and stomach contents of the coyote reveals that it preys more heavily on cottontails than on any other wild species. Remains of several cottontails eaten by raptors were found in the sage belt.

In April, 1951, many young cottontails were found dead on roads in the sage belt, and a newly born cottontail was in the stomach of a coyote trapped four miles north of Claremont, on February 7, 1952.

Specimens examined.—Total, 3, distributed as follows: Los Angeles County: mouth of San Antonio Canyon, 2000 ft., 1 (PC). San Bernardino County: 2 mi. NW Upland, 1600 ft., 2 (PC).

Sylvilagus audubonii arizonae (J. A. Allen)

Audubon Cottontail

This subspecies was recorded on the interior slope from 5200 feet elevation, as at the head of Grandview Canyon, down into the desert, and was common in the sagebrush flats of the upper pinyon-juniper association. Piles of feces under thick oak and mountain-mahogany chaparral indicated that the rabbits often sought shelter there. Adequate cover is a requirement for this rabbit on the desert slope of the San Gabriels; in the juniper and Joshua tree belts the species occurs in washes where there is fairly heavy brush, and only occasionally elsewhere. In the foothills, when frightened from cover in one small wash cottontails often run up over an adjacent low ridge and seek cover in the brush of the next wash. In the wash below Graham Canyon tracks and observations showed that cottontails were taking refuge in deserted burrows of kit foxes.

In the pinyon-juniper association cottontails and jack rabbits probably occur in roughly equal numbers, but in the Joshua tree belt cottontails seem far less numerous than jack rabbits. In the course of a two hour hike in lower Mescal Wash, at about 3500 feet, eleven jack rabbits and two cottontails were noted.

Specimens examined.—Total, 2, distributed as follows: Los Angeles County: 6 mi. E and 1 mi. S Llano, 3500 ft., 1; Mescal Canyon, 4800 ft., 1.

Sylvilagus bachmani cinerascens (J. A. Allen)

Brush Rabbit

Brush rabbits inhabit the Pacific slope of the mountains from about 1200 feet in the coastal sagebrush belt up to at least 4500 feet in the chaparral, and are the only lagomorphs found commonly above the lower edge of the chaparral association. Here they were often on steep slopes beneath extensive and nearly impenetrable tracts of chaparral.

The ecologic niche of the brush rabbit is in brush where the plants form continuous thickets with little open ground. In the coastal sagebrush flats, areas supporting only scattered bushes are uninhabited by brush rabbits, while areas grown to extensive tracts of brush harbor them. When the brush rabbit's mode of escape from its enemies is considered, the reason for their habitat preference becomes more clear. Almost invariably these rabbits seek escape by running through the densest portions of the brush, never appearing in the open; in this way they travel quickly away from the source of danger without being observed. Because they avoid being seen in the open, and do not seek safety largely through running ability, they need continuous stretches of brush for escape. While hunting in the coastal sagebrush belt I have repeatedly seen frightened brush rabbits turn and dart beneath the bushes a few feet from a human being rather than be driven into the open.

A great horned owl shot in March, 1951, in the sage belt, had in its stomach the remains of a freshly killed adult brush rabbit. Although coyotes and brush rabbits often occur in the same general sections of the sage flats, remains of these rabbits have been notably scarce in coyote feces from these areas. This is probably because the coyote hunts along clearings and in open brushland, precisely the type of habitat avoided by brush rabbits.

Family SCIURIDAE

Sciurus griseus anthonyi Mearns

Western Gray Squirrel

Gray squirrels were on both slopes of the San Gabriels in oak woodland. A gray squirrel was observed in April of 1948, as it climbed a telephone pole adjacent to an orange grove near Cucamonga. This, and one noted bounding up a slope of greasewood chaparral near Cattle Canyon, were the only gray squirrels seen in areas which were not grown to oaks or adjacent to oak woodland. In the lower foothills gray squirrels were invariably found in association with valley oak, this plant forming limited woodland areas in canyon bottoms. In the upper chaparral association the squirrels frequented the large scrub oaks growing on talus slopes and canyon sides. In the yellow pine woodland, gray squirrels are restricted to black oaks, often where they formed mixed stands with the conifers. On the interior slope these squirrels were found only at the lower edge of the yellow pine woodland where black oaks are common. There, in the vicinity of Big Pines, they were present between roughly 5800 and 7000 feet, while on the Pacific slope they inhabited oak woodland from 1600 feet to about 7000 feet elevation.

In Live Oak Canyon in December of 1950, tracks indicated that a bobcat had killed a gray squirrel in a small draw beneath the oaks. In Evey Canyon on March 6, 1951, while watching for bats at late twilight, I observed a gray squirrel traveling through the branches of a nearby oak. A great horned owl glided into the oak in an attempt to catch the squirrel, which leaped quickly into a dense mass of foliage and escaped. For roughly ten minutes the owl perched in the oak watching its intended prey, then flew off down the canyon amid frantic scolding by the squirrel.

On March 17, 1951, a female gray squirrel taken at about 3500 feet elevation in San Antonio Canyon contained two embryos, each roughly 40 millimeters long.

Spermophilus beecheyi beecheyi (Richardson)

Beechey Ground Squirrel

From the coastal sage belt, into the yellow pine forest of the Pacific slope, this species is common on land cleared by man or disturbed in the course of construction, or on severely eroded slopes where the original climax vegetation is partly or completely absent. Thus in the sage belt, ground squirrels live along dirt roads through the brush, on the heavily eroded banks often found in the foothills, on land grazed closely by sheep, and in those parts of major washes such as San Antonio and Cucamonga washes where scatterings of huge boulders offer prominent vantage points. In San Antonio Canyon Spermophilus was restricted to the vicinity of roads and firebreaks, and an especially large colony of at least forty individuals lived at a dump one mile southwest of Camp Baldy at about 4500 feet elevation. Ground squirrels used burned stems of large laurel sumac as observation posts. Because of a preference for open areas offering unobstructed outlooks, ground squirrels originally probably did not penetrate the main belt of heavy chaparral on the Pacific slope of the range except in some of the large washes.

In the spring of 1951 and the preceding summer there was a marked increase in the ground squirrel population near Padua Hills as a result of sheep grazing on approximately one-half square mile of sage land. Grasses and smaller shrubs were eaten down to the ground, and in some places coastal sagebrush and Haplopappus were killed by browsing and trampling. The area formerly had a sparse growth of bushes with intervening growths of tall grasses and one colony of perhaps 20 ground squirrels; but after the sheep grazing the area was open brushland with large clear spaces on which the herbage was trimmed to the ground, and had at least four colonies of ground squirrels as large as the first. Also there were other ground squirrels established in various parts of the area. Probably the dry weather in the winter of 1950-51 with consequent retardation of the vegetation aided the spread of the squirrels in this area.

In the sage belt, most ground squirrels are dormant by December. In 1951, after a mild winter, squirrels were noted on January 25 near Padua Hills. On February 8, 1951, males in breeding condition were collected, and on March 16, a female taken near San Antonio Wash carried three small embryos. In early March of 1951, ground squirrels were active at 4500 feet elevation in San Antonio Canyon.

Specimen examined.—Los Angeles County: 1 mi. S and 2 mi. E Big Pines, 8000 ft., 1.

Spermophilus beecheyi fisheri (Merriam)

California Ground Squirrel