170 
JOUENAL OF MAMMALOGY 
numbers in caves, hollow trees, and old buildings. In the case of the 
former class, few of us are qualified to talk at great length. Our experi- 
ences are limited to a Myotis darting from a hole in a stub, a Pipi- 
strellus slipping at dusk from a cranny high on a cliff, or perhaps a 
Nycteris hanging motionless in a fruit tree. The expert collector can 
identify the majority of his chiroptine acquaintances on the wing, but 
this knowledge cannot be transferred to print, and the opportunities 
for further enlightenment are so few that only an observer of long ex- 
perience is qualified to add much of value to the life-histories of the more 
solitary bats. Even in the case of those species with which I am most 
familiar, there has been so little complementary work done by others 
that many of my deductions and theories may have to be revised at a 
later date. Some of. them are here offered tentatively, in the hope 
that others will be encouraged to delve deeper, as their opportunities 
permit, into this fascinating branch of investigation. 
Most of the better known species of European bats are non-migra- 
tory and spend the winters in more or less complete dormancy. In 
fact, I believe that direct evidence in favor of migration has been ob- 
tained in the case of only a very few European forms, and continental 
naturalists received with considerable surprise the evidence that certain 
of our boreal species do perform extensive migrations. However, 
American students have been rather slow to follow this lead, and seem 
loath to believe that except in southern districts, most of our forms are 
migratory. Why not? A few have been reported in hibernation, but 
these reports are very rare and it is more logical to suppose that the 
majority migrate. I am not prepared to state that none of our Cali- 
fornia bats hibernate; and, conversely, that as a rule, all migrate; but 
I do believe that all except the mastiff (Eumops) are migratory to some 
extent, and that species may retire from the more northern boundaries 
of its range during the coldest weather. Most of our summer bat popu- 
lation is absent during the winter and its place is then taken by forms 
from farther north or from higher altitudes. 
With us, it is the rule that all early flying bats are of the small-eared 
species, while the large-eared ones, unless some special method of feeding 
brings them out, fly later. The exception is Antrozous, which is often 
awing ten minutes before it is too dark to shoot; but this bat feeds 
extensively upon the flightless Jerusalem cricket {Stenopelmatus) ^ 
where these occur and the large ears probably enable it to catch the 
faint sounds made by the crawling insects. In California, Eptesicus 
is a very early flier, while in the East it appears at late twilight; so the 
