LITTLE CALIFORNIA BAT Myotis californicus californicus (Audubon and Bachman)

Field characters.—Size small, much smaller than House Mouse (slightly larger than Merriam Bat, about 1/3 size of Large Brown Bat). (See pl. 21c.) Total length about 3 inches (75-80 mm.), tail about 1-1/2 inches (30-39 mm.), hind foot 1/4 inch (6-7 mm.), spread of wings about 8-1/2 inches (220 mm.). Coloration dark brown above, slightly paler on under surface; flight membranes, ears, lips, and muzzle brownish black. Flies with rapid fluttering of wings and marked indirection of course.

Occurrence.—Common in Upper Sonoran and Transition zones on west slope of Sierra Nevada. Recorded from Pleasant Valley eastward to Yosemite Valley. Extreme altitudes, 600 and 4500 feet. Forages about foliage of oaks and other trees, and around larger brush plants; keeps usually less than 25 feet from the ground. Not colonial.

The Little California Bat is probably the most common of the bats in the Yosemite region. It is relatively abundant on the floor of Yosemite Valley and so is likely to come to the attention of summer visitors there who go walking beneath the oaks and pines at twilight. This species does its foraging close about the foliage of the trees and larger shrubs, and ordinarily it stays within a few feet of the ground. It is seemingly oblivious to human presence, so that its actions may be watched at close range.

Often this is the first species of bat to appear abroad in the evening, though it is sometimes preceded by the Merriam Pipistrelle. At El Portal on November 22, 1914, a Little California Bat was out at 5:10 P.M. At Pleasant Valley, late in May (24th to 27th) of the year following, the species was still among the first to appear, though at that season individuals did not come out until much later, 7:25 to 7:45 P.M. The strength of the light was about the same at the two hours mentioned. The bats evidently stayed in their retreats for some 2-1/2 hours longer in summer than in winter.

Little California Bats are to be found in the Yosemite region throughout the year. Our records include nine of the twelve months and are so distributed as to indicate continued residence by the species, at least below the 3500-foot contour. But whether the same individuals are present at all seasons or whether, like the fox sparrows, the summer population moves out and is replaced by another contingent which comes in from the north and winters here, is a point still to be determined. In Yosemite Valley bats believed to be of this species have been seen out as late as October 27. At Pleasant Valley the species was recorded abroad definitely on December 5 (1915), and a dead individual was picked up on Smith Creek, 6 miles east of Coulterville, on February 7, 1916.

These bats find shelter in a variety of situations. In Yosemite Valley, at 6 P.M. on August 10, 1915, a Little California Bat, after circling over and drinking at a pool near the foot of Yosemite Falls, was seen to take refuge in a crevice between boulders. On May 30, 1911, the smoke of a fire built in a rocky cavern near the foot of Illilouette Falls routed out a Little California Bat which had been hanging in a crevice overhead. A number of these bats have been found on or in the walls of old wooden buildings and a few have been discovered in crevices in pine trees. Under original conditions as well as at the present time the species was probably very adaptable in its choice of shelter.

Bats are active only at twilight and after dark. Their daytime retreats are often difficult of access or unknown and their capture is neither easy nor sure. It is therefore more difficult to gather information concerning them than concerning birds and most other mammals. For these reasons the body of accurate knowledge accumulated by naturalists is much less complete for bats than it is for many other forms of animal life, despite the fact that, in many cases, a disproportionately large amount of time has been devoted to their study. While our parties were engaged in field work in the Yosemite region one or more members would be out almost every evening attempting to shoot the bats seen coursing over lakes or ponds, or across openings in the forest; and every clue concerning the location of "roosts" was eagerly followed up. Yet our total collection of bats from the Yosemite region numbers only 80 specimens, most of these being of 2 of the 9 species represented.

The wing of a bat is a thin elastic double membrane or skin which stretches between the greatly elongated 'fingers' of the forelimb and between the fifth of these and the body of the animal. The hind limbs and tail are included in this flight membrane so that the total expanse when extended is many times that of the body alone. By moving the forelimbs the bat is able to fly, and its passage through the air seems much better controlled than in the case of most birds. Most birds must dart through the air at a relatively high rate of speed in order to maintain themselves aloft, and even the swallows, which like bats feed on flying insects, must perform long sweeps through the air. The bat is able to fly fast or slowly, to turn sharply, and to check its flight abruptly, if occasion demands. It can thus control its passage through the air with greater precision. When not in flight a bat clings, head downward, to some upright surface, using for this purpose the slender, curved, and sharply pointed claws of the hind feet.

The wings of a bat are provided with numerous sensory hairs which upon being struck by air waves apprize the animal of the location of objects in its vicinity; and this fine sense of touch, if such it may be called, is the basis of the bat's ability to course about in twilight or even in pitch darkness without striking objects as would a mammal or a bird which is dependent solely upon sight. The ears of bats are proportionately large (see pl. 21 and text figs. 7, 8), and these big external conchs probably catch sound waves made by flying insects and thus the bat becomes aware of the direction of objects of prey.

Bats spend the day in some sort of retreat, the location chosen being more or less different for each of the different species. But such retreat is never dug or modified; nor is any bat known to make a nest as do so many other nocturnal mammals. Some species such as the Free-tailed and Pallid bats are characteristically colonial; others, such as the Little California Bat, are usually, but not always, solitary; while the Hoary Bat seems to be strictly solitary. Each species issues forth when the light of day has reached a certain degree of weakness—a different degree for each species—and once abroad, each hunts its prey in a rather definite niche. The pursuit of prey usually occupies only a short period at and after dusk, though additional foraging may be done just before daybreak. The daytime hours and, with most species, the middle of the night are spent in rest. Bats are therefore abroad and active less than almost any other sort of animal; this is likely made possible, in part at least, by the concentrated nature of the food upon which they subsist.

The method used in collecting bats may be illustrated by giving the circumstances under which a Little California Bat was taken at El Portal on November 20, 1914. Well before twilight the collector had taken up a station in the open where a clear view was obtainable. The first bat seen abroad on that evening was a Hoary Bat, noted at 5:10 P.M. Up to 5:35 four more bats, all small, the size of the Little California Bat, were seen. Twice, as these small ones crossed low places in the horizon line, and so could be seen against the sky, loads of dust-shot were fired at them. In the case of the one bat obtained, the collector fired his gun in the general direction taken by the bat after it passed the clearing; it just happened that the animal had continued its flight in a straight line. A soft thump told that the bat had been dropped. The collector lined it up with a distant object, dragged the toe of his shoe to leave a location mark, walked forward, and then at the judged distance began working over the ground in concentric circles, picking up every dark object—until his fingers encountered the soft body of the bat.

All our bats are strictly insectivorous. The food of the Little California Bat, so far as we know, consists solely of flying insects. Because of their crepuscular habits bats are able to feed upon an entirely different category of insects than are the day foraging insectivores, the swallows, swifts, flycatchers, etc. Their forage comprises to a considerable extent beetles and moths, and since the larvae of these are often destructive forest pests, the bats are thus of material service to the trees. In truth the bats constitute one big arm of the "night patrol."

A rather unique departure in forage range was noted in the case of a Little California Bat at Pleasant Valley early in December, 1915. The house in which a member of our party was quartered there had on one side a large shed-room in which were unusually large numbers of house flies. At dusk, when the flies were buzzing about slowly and seeking warm resting places in which to spend the night, a Little California Bat would come forth from its daytime retreat and course back and forth in the room, where it found easy forage in the logy flies. All too soon, to the naturalist's way of thinking, the bat had captured enough flies for its evening meal and retired.

During the late summer and autumn months bats, as a rule, become very fat. In all probability this storage of excess nutriment is an adjustment to provide against winter and early spring when forage is scarce or when the weather is such that bats cannot venture out to feed. When collecting specimens during October or November, it is a rather common experience to find bats so fat that when they are shot the 'oil' begins at once to ooze out of the shot holes and, by the time the collector has retrieved his specimen, the fur of the bat will be matted with the grease. During periods of unfavorable weather some species of bats go into dormancy, a condition of reduced animation resembling that of hibernating chipmunks. But we learned nothing in this regard concerning the bats of the Yosemite.

The young of the Little California Bat are born during the early summer months. A female taken at Pleasant Valley May 21, 1915, contained one large embryo; and in a group of these bats secured on July 13, 1920, there were five females each accompanied by a single youngster one-third to two-thirds grown. With this bat, young are borne but once each year, and there is only one young at a birth. These facts indicate that the existence of the species is relatively a very safe one—assuming of course that the birth rate has been adjusted to the maximum 'expectation' of casualty.

On July 13, 1920, an examination of the deserted, windowless buildings at the McLaughlin mine south of Dudley revealed the presence of eleven Little California Bats. Those mentioned in the preceding paragraph were of this lot. These bats were found by systematically ripping off the muslin-mounted wall paper. They were on the west side of the building where the wall was shaded on the outside by trees. Much previous pounding on the walls of other parts of the building had not disturbed them in the least. The bats were not clustered together, as is typical of colonial species, but were clinging individually to the rough boards beneath the loosened wall paper, within a circle 2 feet in diameter and only about 30 inches from the floor. There were five adult females (all in nursing condition) and five young (three females and two males). The young were clinging to the walls independent of, but close to, their mothers. Off to one side was a female without any young one. Later, when confined together in a box, two of the adults were found each with a young one attached to a nipple. The young ranged in weight from 1.6 to 3.0 grams, while the weight of the adult females averaged 4.3 grams.