Bird Haunts and Nature Memories/Chapter 8
Daubenton first described the noctule, or great bat, but it was Gilbert White who identified it as an inhabitant of Britain. He called it Vespertilio altivolans "from its manner of flying high in the air," a characteristic which, though by no means invariable, is very useful as a means of identification. The noctule is the largest British bat, considerably bigger than its near relative, Leisler's bat, and slightly exceeding the greater horseshoe and serotine. The evidence of the occurrence of the mouse-coloured bat, V. murinus, in England is so slender that it cannot be accepted as a native. The name V. murinus was for long applied to the "common bat," the pipistrelle, showing how little intercourse existed in the early part of last century between the British and continental naturalists, for the mouse-coloured bat was well known then as the common bat of the Continent. It is strange that there should have been confusion between animals that varied so much in size as this bat and our little pipistrelle. The expanse of the outstretched wings of the noctule reaches 13 or 14 inches, and as it flies before the light has faded, often before the swifts have vanished, it is a conspicuous object against the evening sky.
Donovan, in 1820, said of the noctule that it "is of a colour far less dismal than that of the common bat," and though the pelage of the pipistrelle is hardly dismal, the fur of the noctule is a beautiful ruddy brown, almost golden at certain seasons. The question of the seasonal and age variation in colour of mammals is not fully investigated, and the researches in bats have yielded little result. Barrett-Hamilton found no evidence of change in the noctule, but thought it probable that the colour was richest just before hibernation—that is, after the season's activity and constant feeding. Old males, I have always found, are far more golden than immature bats. These aged males, at the height of the breeding season, are wonderfully sleek and glossy. Donovan's picture of the noctule was, I hope, drawn from memory; the colour is curious, and it possesses a leaf nose not unlike a vampire, whilst the tragus is depicted as long and pointed instead of short and rounded. Bingley's plate, published in 1809, is far better. The Rev. W. Bingley is little known as an authority on British animals, but of mammals in particular he was a careful observer, deserving a better reputation than he enjoys. At last we can boast good figures of our British bats, for Mr. Thorburn's lifelike pictures can hardly be improved.
The noctule emerges from its winter slumbers in March or April, and it is usually the beginning of the latter month before it is much in evidence; it has been seen flying in February and exceptionally earlier. In September, if the weather is suitable, it is abundant until the end of the month, and often is abroad regularly in the early part of October, but a November noctule is rare. 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, but as time is precious the bat wastes no time in getting to the scene of action. The speed of flight varies considerably, but is usually rapid and straight, though varied with occasional dashes from side to side and sharp oblique dives. These erratic movements are, almost certainly, due to the fact that the bat has become aware of an insect at another level or on a lower plane. Bell thought that they were caused, at any rate when the descent was sudden, by the loss of balance if the bat had caught "some large or intractable insect," and Grabham enlarged on the idea and described the noctule using its thumb to tend asunder the prey it was carrying. If the drop is closely observed it will be seen to be not only direct, but oblique; it is a dive, not a fall.
Noctules frequently chase one another on the wing, squeaking vigorously, and almost the whole time that they are abroad they keep up incessant noise. This sound, a high, shrill squeak, is uttered in the roost before they emerge and after they have returned; Alcock points out that the note may be imitated by striking a halfpenny smartly with a sixpence. Bats are erratic about their appearance in the evening; some nights hundreds are visible, on others hardly one emerges. Doubtless to some extent this irregularity is due to weather conditions, cold, wind, or rain keeping many indoors; but a few go abroad in stormy weather, and at times there are few to be seen on evenings which are apparently suitable.
The noctule has a curious smell, which White and Donovan thought "fetid," but though strong it is not really offensive; it has given rise, so some think, to the name "fox-bat," but that may have originated in the colour of the pelage.
The habits of any creature which comes abroad at night or in the half-light of evening are not easy to observe, but so easily does this bat adapt itself to the restraint of captivity that it is strange that so little is known about its ways. Of all bats, except perhaps the long-eared, this species is the least difficult to keep under artificial conditions. It requires no taming process to induce it to feed; it rapidly connects human fingers with the food that they supply, though it does not seem so easily to recognise that the finger itself is inedible. When captured or wounded the noctule bites fiercely, and though its teeth do not make a serious wound they draw blood, for they are exceedingly sharp, and the jaws which can scrunch the hard armour of dor or cockchafer are powerful. For weeks I have kept noctules in a box, releasing them for exercise every evening. There were nineteen in the hollow from which some of my captives came, and of these sixteen were males; that looks as if the sexes form separate colonies. Almost immediately that the captives were placed in their new home they took food from my hand. The best beloved food was the mealworm; the larva of a beetle; this they preferred to their natural diet of dors, or big-bodied moths. Mealworms can hardly be looked upon as natural food, for the larvæ of beetles cannot come in the way of animals which feed upon the wing; yet it is the food which, once tasted, no bat can resist.
In a very short time my noctules would scuttle across the table to my hand when I offered mealworms, but so frequently did they fix their sharp teeth in my fingers that I began to offer the gift from between forceps. There was no suggestion of anger in this attack; it was merely anxiety to get as much food as possible in a short time. But there was one interesting fact apparent: as the bat feeds in flight, it never seemed to realise that it could recover food that it had dropped; it would walk over a maimed and struggling worm to ask for more. The long-eared bat, which often captures insects at rest, would hunt on the floor of its cage for an insect which had escaped.
When the box was opened in the daytime or early in the evening the bats were comatose, and it took time to awaken them; but later, if left to themselves, they roused and became lively. If neglected during this wakeful period, usually less than an hour, they relapsed into lethargy, and later had to be roused for food; and indeed the normal diurnal sleep of bats seems as profound as the winter slumber which we call hibernation. Alcock found that the breathing became shallow and irregular—"Cheyne-Stokes'," he calls it—and that the temperature rises as much as 31° in fifteen minutes, and it often took that time to induce full activity. I would take a bat in my hand to warm it, and in a few minutes its breathing became rapid, the whole animal panting and shuddering as if in fear; it pumped itself awake. When really roused its whole being changed; its body felt hot, its eyes gleamed, its sensitive ears were in constant motion. Raising itself on the carpal joint it would patter towards me, and if I kept it waiting would climb my arm, snuggle for a few seconds at the back of my neck, and then take wing for its evening exercise. As a rule, however, they were in no hurry for flight, but after a good feed and along drink—for they are thirsty creatures—they liked a short flight round the room. They would lap water from a saucer or suck it from the end of a camel's-hair brush. Raw meat they took if shredded fine, and bits of ﬁsh were also appreciated, but they required teaching before they tackled these unusual viands; what is more, they found them more difficult to masticate than the horny skins of beetles and mealworms.Mealworms, small moths. bluebottles, and some beetles are tackled and eaten without difficulty, but a dor or a chafer had to be overcome. and large noctuid moths were the most difficult captives. When the bat is walking or at rest the tail is carried in a curve, the tip often under
the body, pointed forwards; the bent tail thus causes the interfemoral membrane to bag, for this membrane stretches from foot to foot, with the tail in the centre. When any large and powerful insect was seized the bat at once thrust its head under its body, pushing the insect into the bag or pouch between is legs and securing a firmer grip. Upon first seizing the insect the bat raised itself, pressing the forelimbs, the wings, to the ground, and bringing the legs forward so as to increase the capacity of the pouch. If the insect was not very strong the head was withdrawn at once and the unfortunate devoured, but a big insect gave trouble, and it might be a second or more before a firm enough grip was secured. The whole movement was quick, and at first we did not realise that it was a normal habit, but there is little doubt that it is what the bat does when on the wing. A moth seized by the wing alone would give trouble in the air, and might easily escape, but if at once thrust into this living net its struggles could be mastered, and the bat could shift its jaws to the body of its prey. Though it is seldom possible to watch this swift action in the flying bat, there are times when we see it dip its head in the air.
When feeding the motion of the bat's jaws is exceedingly rapid, and the crunching of the hard beetle elytra may be heard as the noctule passes overhead. The process of devouring a beetle is more interesting than pleasant to watch, for though the strong jaws move quickly the insect passes but slowly down the throat; its still undevoured limbs twitch long after much of the body is no more. Bingley noticed this habit of pouching food in a small bat, to which he had given a flesh-fly: "The animal, raising itself higher than usual on its fore-legs, bent its head with great dexterity under its belly, and forced the insect into its month, by thrusting it, from side to side, against that part of the membrane which extended betwixt the two hind-legs." Thus more than a hundred years ago the observant parson saw an action which later naturalists ignored; but it is evident that the use of the interfemoral pouch is not to force the prey into the mouth, but to secure such a hold upon it that it shall not escape.
After food and exercise the noctules invariably performed an elaborate toilet before retiring once more. The ablutions were performed as they hung by one leg; with ease they reached every part of the body or wing membrane with the other leg, combing out the fur, scratching the back, head, or belly. They sucked their toes as they combed, washing and brushing at the same time, and twisting into curious positions, swinging from side to side.
My male bat took more vigorous exercise than the female. He seldom struck an object, but would sometimes brush lightly over my head as he passed. Once he touched an electric globe, but he circled round and round the wire without stirring it. Unlike some bats, which can reverse in the air, he invariably alighted on an upright object head uppermost, clutching first with his thumbs, but instantly shuffled round and took hold with his feet, thus hanging in the most convenient position for a renewal of flight.
How the flying noctule becomes aware of the presence of prey, when both are passing rapidly through the air, is not easy to understand, especially as we cannot be sure how perfect is its eyesight. Experiments with other bats have satisfied me that the power of vision differs considerably in the various species. The big-eyed, longeared bat certainly seems to see well; the horseshoes, in which the little eye is almost hidden in the fur, certainly see but little. The noctule uses its eyes, but it may be short-sighted. One thing is certain, its hearing is good, and the vibration of an insect's wing may set up notes which it can appreciate when we are unable to hear them. The greatest horseshoe locates its flying prey by hearing, and possibly the noctule does the same. When my bats were fully awake a loud noise, such as that caused by dropping a book, kicking the leg of the table, or shooting, caused them no annoyance; but the scratch of lighting a match, a sudden hiss, or similar low note always startled them. It was interesting to note what sounds caused their ears to twitch and made them raise their heads.