216 MAMMALS 
was over, for though the wind was still favourable 
and many remained in the spider belt, these had 
apparently used up all their energy and made no 
further attempt to escape. 
About the migration of mammals I can only say, 
from my own observation, that bats are strictly 
migratory all over the pampas. Everywhere in that 
flat country of some 60,000 square miles extent, bats 
appear with the birds in spring, arriving later than 
the early spring visitors, and vanishing with them 
in March and April. Anyhow, I never found a hiber- 
nating bat nor heard of one, although they were 
abundant all the summer, hanging in the trees by 
day, where in an hour or two I used to be able 
to find and capture a dozen or twenty, just to 
release them in a large room to observe them 
in confinement. 
It is, however, my considered belief, which may 
go for what it is worth, that the impulse and disquiet 
is in mammals as well as in birds, fishes and insects, 
albeit it does not lead to actual migration except in 
some species and on rare occasions. 
I have long suspected that our common little shrew 
is powerfully moved by the impulse at the end of 
summer, as invariably from July onwards and through 
the autumn months dead shrews are found lying on 
roads and other open bare spaces; and this is not the 
case only here in England, but all the world over 
where the animal is found, in Europe, Asia, Africa 
and America. It is possible that the little creatures 
are subject to a mysterious malady which kills them 
