MERRIAM BAT. Pipistrellus hesperus merriami (Dobson)

Field characters.—Smallest bat in the Yosemite region (about three-fourths size of Little California Bat). Total length 2-1/2—2-3/4 inches (67-72 mm.), tail 1-1/4 inches (29-30 mm.), hind foot about 1/5 inch (5 mm.), ear 1/3 inch (9 mm.), spread about 7-3/4 inches (197 mm.). Coloration warm buff above, paler beneath; flight membranes, ears, lips, and muzzle black. (See pl. 21b.)

Occurrence.—Common in Upper Sonoran and lower part of Transition zone on west slope of Sierra Nevada. Recorded from Pleasant Valley eastward to floor of Yosemite Valley. Forages in the open, well above the smaller trees.

The Merriam Bat, smallest of the local bats, is a species likely to be seen by anyone who visits Yosemite Valley or the neighboring country to the west. It appears early in the evening, being usually the first species to be seen abroad, and flies high, in the open air, well above the horizon line. Its flight is notably irregular, even for a bat, and this feature alone often serves to identify a solitary individual when comparisons of size cannot be made. The pipistrelle finds shelter in crevices among the rocks, and of such retreats it has a wide range for choice in the Yosemite.

On the evening of July 24, 1915, one of our party went bat hunting near Rocky Point, on the north side of Yosemite Valley. The first bat seen, at 7:18, was shot and proved to be a "pipistrelle." It was flying high in the open among the yellow pines and black oaks, but well away from the foliage of these trees. No other bats were seen that evening until 7:30 when the Large Brown and the Free-tailed appeared simultaneously.

This bat is evidently resident in the foothill districts throughout the year, as a specimen was shot at El Portal on the evening of January 1, 1915. Its continuance in the Yosemite Valley during the winter season seems doubtful; no bats, of any species, were noted there after the end of October.

At Pleasant Valley on May 22, 1915, a female Merriam Bat was obtained which contained 2 embryos.