1918 | Grinnell: A Synopsis of the Bats of California 235 
in sight at one time. The manner of flight was quite unusual, for 
instead of the erratic zigzag course commonly followed by bats when 
seeking their food at dusk, the flight of those noted on this occasion 
was very steady, consisting chiefly of a sailing or drifting motion, 
with occasional short flappings of the wings. The height above the 
ground was estimated as varying from one hundred and fifty to four 
hundred feet. With the aid of a glass three different sizes were noted, 
but of course it was quite impossible to identify the species. The 
flight lasted for over an hour and more than one hundred individuals 
were observed. 
Howell suggests the possibility that such diurnal migrations are of 
regular occurrence, but if that be so, it seems remarkable that they 
have not been more frequently observed. 
Food and Feeding Habits——There are among bats species which 
eat fruit, some which eat fish, others which subsist upon blood, and 
lastly, and by far the most numerous, are those species which eat only 
insects. The bats native to California are, with one possible excep- 
tion (see under Macrotus californicus, p. 257), strictly msectivorous. 
Campbell (1913, p. 1176) states definitely that bats will eat pieces 
out of hams and bacon left in smoke houses. I know of no other refer- 
enee to such a habit, outside of nursery rhymes. 
Most of our bats catch their prey upon the wing and devour it 
without alighting. As they eat the insects they bite off and reject the 
hard parts, which fall to the ground. The soft edible parts are very 
finely triturated by the sharp teeth, so that it becomes quite difficult 
to identify the insect remains found in the stomach of a bat. How- 
ever, one California bat, Antrozous pacificus, brings at least the larger 
of its insect victims to its roosting place, and hangs there while eating. 
From the insect remains on the floor beneath the roost it is a simple 
matter to learn the nature of the food (see p. 355). 
At least two British bats (Barrett-Hamilton, 1911, p. 172) hold 
the tail curved beneath them in flight, and one of them has been 
observed to use the sac thus formed by the interfemoral membrane as 
a pouch into which it thrusts a struggling insect until it has secured 
a firm grip upon it. It would be of interest to learn whether any of 
our species share this habit. 
As is the case in other groups of mammals, all our bats become 
very fat in autumn. Specimens secured in late winter or early spring, 
on the other hand, are invariably lean. The fat stored up in the fall 
is absorbed during the period of hibernation or emigration. Those of 
