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Mammals of Yosemite National Park (1952) by Harry C. Parker

BATS

Bats are probably more numerous in Yosemite than an unobservant person may realize. They may be seen every evening about twilight, or, in some species, earlier, in warm weather, flying back and forth over the river or the meadows in Yosemite Valley. They may be heard squeaking overhead whilst the camper enjoys his after-dinner fire. In half an hour’s ride in an open car, approaching Chinquapin from the south, a friend and I once counted more than fifty bats flying over the roadway, where they were silhouetted against the gradually darkening sky.

From “Mammals of Lake Tahoe” by Robert T. Orr, California Academy of Sciences. LITTLE BROWN BAT

The bat’s wing is formed from the bones of the hand and arm, with a leathery membrane stretched across this framework and connected to the hind legs and tail. When at rest, the wing can be folded up, much as an umbrella closes.

Bats are the only mammals that truly fly. Many people consider them as flying mice. That this has probably always been so is reflected in the German word for bat, Fledermaus, or “flying mouse.” However, we already know that the skull and teeth belie this belief (see pp. 54, 55). Indeed “flying insect trap” more nearly describes our Yosemite bats.

There are many other folk tales about bats that have no foundation in fact. For instance, they will not normally fly into a person’s hair. For years, ranger naturalists have spoken on the platform at the summer evening programs at Camp 14 [Editor’s note: Lower Pines Campground—DEA.], while bats swooped to and fro behind them, catching insects that were attracted by the light on the picture screen. Yet never has a bat flown into the hair of a speaker. Once I stood with four other men in the bat cave of Carlsbad Caverns beneath a blanket of bats estimated at 15,000 individuals, which clung to the ceiling. In the course of our investigations, this mass was agitated into flight, yet at no time did they endeavor to get into our hair.

From Kodachrome by Anderson Head of Pacific pallid bat. Note the eye.

We have heard the saying, “blind as a bat.” Some carry that thought further and believe that bats have no eyes. However, they do have eyes, rather well-developed ones, though comparatively small.

Since most mammals that are active at night have rather large eyes, the question arises as to how bats can fly with such sureness through the branches of trees and avoid other obstacles in the dark. For that purpose, the eyes seem to be of little assistance to bats. Tests have been made with blindfolded bats in rooms crisscrossed with wires and the animals flew about, rarely hitting the barriers. However, when the ears or mouth were plugged, blunders were quite notable. It seems that bats in flight emit sounds of a frequency too high for the human ear to detect. By listening to the variations in the echoes of these sounds, a bat is warned of obstacles in time to avoid them. These sounds should not be confused with the high-pitched squeakings that are often heard from bats.

During the daytime, Yosemite bats hide in rock crevices, caves, buildings, and trees, where they hang upside down and sleep. This upside down posture is facilitated by the strongly curved hind toes and claws. In the winter, some of our bats hibernate, while others migrate to a more temperate clime.

From Kodachrome by Anderson Wing of Pacific pallid bat. Count the fingers.

While the babies are quite young, they cling to their mother when she is at rest, and she may even carry them with her when she flies forth to forage for food. As they grow stronger, she usually leaves them clinging to a sheltered place where she returns after her trips for food. They grow very rapidly and are hunting for food themselves when but a few weeks old.

Yosemite bats feed entirely on insects, which they chiefly garner while on the wing. Water is usually taken by swooping low over the surface and scooping it up. All of the bats in the United States are insect eaters. Since an individual bat may consume a quarter of its own weight in one meal or half its weight in a night, we may assume they are generally beneficial to the interests of man.

In size the Yosemite species range from the tiny Merriam canyon bat, which is less than three inches long with a total wingspread of less than eight inches, to the California mastiff bat, with a total length of 6 1/2 inches and a wingspread of 19 inches. This is the largest species in the United States.

Photo courtesy Museum Vertebrate Zoology, University of California The spotted bat, rarest Yosemite mammal.

One of the rarest mammals, the spotted bat, has been found in Yosemite Valley on two occasions. These are two of only ten specimens known to science. One was found in August 1931, by the cook at the Government mess hall, hanging under the eaves of the building. The other was found by the son of a visitor in Camp 15 [Editor’s note: former Upper River Campground—DEA.], August 13, 1951. Anyone finding such a bat in or near the park should immediately bring it to the attention of the Yosemite Museum staff.

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