Page:The Zoologist, 4th series, vol 5 (1901).djvu/77

Rh The time at which the first Bat issued from the hole varied from twenty-eight minutes after sunset, on April 21st, to seven minutes before sunset, on Aug. 14th. The Bats leave the den in rapid succession—on Aug. 27th twenty-two emerged within a minute—but their return is much less regular. This is probably due to the varied success of individuals in obtaining food. During August and September, at any rate, on fine still evenings, the duration of the vespertinal flight is sometimes less than an hour; on Aug. 27th a Bat entered the den fifty-five minutes, and on Sept. 4th fifty-seven minutes, after the first had emerged. On each evening, however, the flight in some cases lasted at least an hour and a half; and on Sept. 5th some of the Bats were absent for more than two hours. It is probable that on wet and windy evenings the duration of the flight is even less than an hour, but I have no data to prove this. It is easy to count the Bats as they leave their den in the twilight, but a difficult matter to make sure of the number that return. They do not often enter the hole immediately on their arrival, but dash round and among the trees, and in many cases pitch several times for an instant on the tree-trunk near the hole. Their advent is proclaimed by the beating of their wings, but even on moonlight nights all that one sees is a form silhouetted for an instant against a patch of sky. When the Bat is flying against a background of tree-trunks or foliage one can see nothing. It is true that faint rustle may be heard when a Bat actually enters the hole, but this resembles the noise made when it pitches for an instant on the tree-trunk, and if two or more Bats arrive together, as often happens, the confusion is increased. A good deal of intermittent squeaking may be heard in the den after the arrival of the second Bat. The following extracts from my note-book describe the course of events on three evenings:—

Sept. 3rd.—Fine moonlight evening; no wind. First Bat emerged at 7.7, followed by twenty-six others before 7.11. Much squeaking for half an hour before they appeared. None seen or heard until 8.22, when one returned and entered the hole, after