OBSERVATIONS ON THE NOCTULE.
In the neighbourhood of Alderley Edge, and, indeed, throughout the wooded parts of the Cheshire Plain, the Noctule, Pipistrellus noctula (Schreb.), is abundant, A hollow tree, or less frequently a house-roof, serves as a diurnal retreat, whence, during the warmer months, the Bats issue to feed soon after the daylight has begun to wane. On fine summer evenings one's attention is often attracted by the shrill squeak of the Noctules which are flying in company with the Swifts, at an altitude difficult to estimate accurately, but certainly not less than from seventy to eighty feet. This squeaking note is pitched so high that it is inaudible to many ears. As the light fades, the Bats descend to a lower level, and feed at a height of from fifteen to thirty or forty feet above the fields, pools, and open places in the woods. The crunching of their jaws as they masticate their insect prey may then be heard distinctly.
The time at which the Noctule issues from its retreat does not always bear the same relation to the hour of sunset, and sometimes differs considerably on consecutive evenings. Wind, temperature, and other atmospheric conditions, rather than the actual hour of sunset, probably determine the time at which the Bats emerge, and the duration of their flight. Rain, if not heavy, does not incommode them whilst feeding, but if the night be cold and windy few or none will be seen. It is probable that individual Noctules do not always resort to the same den throughout the summer, for the numbers which emerge in the evening are not constant, and even on consecutive evenings, when the atmospheric conditions appear to be identical, the number sometimes varies considerably. On the other hand, it is possible that on some evenings the whole strength of the colony does not turn out, and that some of the Bats remain in the den all night.
On April 5th, 1896, Mr.and I watched Noctules sallying forth for their evening flight from a hole beneath the