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)