The duration of flight is remarkably short, a habit shared with its Irish representative, Leisler's bat.
Mr. C. Oldham in England, and the late Dr. N. Alcock in Ireland, by careful watching, confirmed the opinion of Dowker that the vespertinal flight lasts for about an hour and seldom exceeds this limit; two hours away from the roost was exceptional. As Alcock pointed out, "a mammal that rests for six months in the year, that only feeds for one hour a day during the other six, spending this hour in rapid and sustained flight—as great a contrast as can be imagined to its previous condition—certainly presents a very curious picture of animal economy." Alcock was reckoning it as active from April until September, but even allowing for a month or two at either end when the bat comes out occasionally, and for a morning hour of energy, the problem is still acute. During the winter sleep noctules herd together in hollow trees or in the roofs of buildings, but in summer the diurnal resting-place is usually a hollow tree. The species has been included amongst the cave bats, but the evidence is not altogether satisfactory. Regular cave-haunting bats, as I have proved or endeavoured to prove elsewhere, frequently move and feed in the caves themselves, and, in the West of England, at any rate, go abroad to feed in winter. There is much that we have yet to learn about the mystery of hibernation, and one by one our ancient beliefs, founded apparently on the best evidence, are subjected to rude shocks. Yet, so far as we know at present, the noctule sleeps very soundly in winter, all its energies latent during that period when flying insects are difficult to obtain.
Directly the bats emerge in the evening they fly straight off to the feeding-ground, a glade in the woods, an open field, or some large sheet of water; the situation varies according to the insects which are the object of the chase,
