56 
JOUENAL OF MAMMALOGY 
was a cluster of varying size in the barn up to the last of August but 
by September first they had dispersed or found another roosting place. 
It will be interesting to learn if they come back next year, if exactly 
the same ones keep together, and if the young return with them or, if 
their numbers are not augmented by the young, as was the case with 
the four banded in 1916. Whether the pipistrelle migrates or hiber- 
nates I am unable to say from my own observations. They appear in 
the spring about the first of May about the time that the migratory 
silvery-haired bats appear, and I have seen them as late as the first of 
November. 
Wliile on the subject of bats I should like to describe a breeding 
colony of the small brown bat, Myotis lucifugus, which I examined a 
number of years ago, July 5, 1907. It was in the attic of a house in 
Homer, New York, 22 miles from Ithaca. The house was of brick with 
a fiat tin roof sloping toward one end, the attic ranging from 18 inches 
to four feet in height. At the lower end of the roof the tin had become 
loosened from the brick, causing a crack of from half an inch to an inch 
in width through which the bats gained entrance. The bats congre- 
gated at the lower end of the attic hanging head downward from the 
roof trusses in large mats. They did not, however, chng to one another 
or form such dense clusters as do the pipistrelles. These masses were 
composed chiefly of adult females and young nearly grown. In one 
place where the roof was scarcely 18 inches from the floor, a large 
cuboidal space had been formed in the brick wall owing to the rotting 
away of a large joist. Here large numbers of the oldest young had 
congregated with a few females carrying young. The place most 
populous with bats, however, and the place where probably all of the 
young were born, was the space above the brick wall and below the 
roof between the trusses. Here the pregnant females had gathered 
in large numbers. From one of these spaces, thirty females were 
removed, all with small young or large embryos. Of course there was 
no pretense of a nest, the young being brought forth on the bare bricks. 
These were moist with urine but the excrement was apparently all 
ejected onto the floor where it had accumulated in piles several inches 
deep. 
No female containing more than one embryo was found although 
some of the females were accompanied by two young of very different 
sizes. In fact there seemed to be three distinct sizes of young in the 
attic of which from thirty-two to thirty-six of each size were secured. 
The smallest had apparently been born but a short time. Of these four- 
