O BROOKLYN INSTITUTE MUSEUM. SCIENCE liULLETIN 2. I. 
months between December and March. From such data we may 
attribute to the Silver-haired Bat and other bats, a type of migration 
analagous to that of many birds, in which the individuals of a species 
within a given breeding range move southward in fall, only to be 
replaced by winter residents of the same species coming from a more 
northerly faunal area- On such an hypothesis, a counter tendency in 
spring would cause a northward flight of the species as a whole, until 
each group had reached its native habitat. 
So long ago as 1887 Dr. Merriam proved that certain tree 
dwelling bats migrate- Records of the presence in winter of the 
Hoary, Red and Silver-haired Bats far southward of the territory 
where their j^oung are born, as well as the occurrence of these species 
in spring and autumn on barren islands off the New England coast 
and on Cape Cod, showed a regular migration. Dr. Merriam's expla- 
nation is that the tree bats retreat southward in order to escape 
severe climatic conditions, while cave species, hibernating in the 
even coolness of their subterranean refuges, removed from the influ- 
ence of both sudden and extreme changes of temperature, tarry in 
northern latitudes all the year. But there is evidence that even 
cave bats migrate, \^'alter L. Hahn, describing his observations 
on the Little Brown Bat {Myotis lucifugiis) in caves near Mitchell, 
Indiana, writes: "Jnst after most of the bats of this species left 
the Shawnee Cave about the end of April, 1907, there was a period 
during which very few were seen flying about in the evening. A 
few weeks later they were seen again in abundance. It seems' 
probable that the animals which wintered at this place migrated 
farther north and that the summer residents had passed the winter 
elsewhere." 
The extent of the seasonal flights of bats, and the degree to 
which the various species partake of the migratory habit are still uncer- 
tain. Presumably the journeys are made chiefly at night after the 
manner of many birds- Arthur H. Howell, however, has recorded a 
diurnal flight observed at Washington, D. C-, between the hours of 
nine and ten in the morning of September 28, 1907. This observer 
watched many l)ats flying steadily towards the southwest at altitudes 
estimated to vary between 150 and 400 feet- In this flight there 
were apparently individuals of the Silver-haired or Red species, as 
well as a few smaller animals, probably the Little Brown Bat or the 
Georgia Pipistrelle, or both. 
Silver-haired Bats, in common with some other species, are fond 
