The Zoologist/4th series, vol 5 (1901)/Issue 716/Observations on the Noctule, Oldham
OBSERVATIONS ON THE NOCTULE.
By Charles Oldham.
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. T.A. Coward and I watched Noctules sallying forth for their evening flight from a hole beneath the eaves of the church at Nantglyn, Denbighshire. The first, which emerged at 7.15, was followed at short intervals by seven others, and at 7.27 between twenty and thirty appeared in quick succession. On several evenings in the spring of 1900 I timed the Noctules as they left their den in the dead limb of a beech at Alderley Edge, and later in the year I made some observations on a second colony which had its quarters in the hollow trunk of a living Scotch fir in the same district. The results are summarised in the following table:—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 pitching for an instant and dashing away again eight times. Others kept dropping in until 9.38, when I left. At 8.49 three or four were dashing round the tree at once. Intermittent squeaking in the den as the Bats returned.
Sept. 4th.—Fine moonlight evening; no wind. The first Bat was out at 6.56. Twenty-three more followed before 7.1. No further sign of Bats until 7.53, when one arrived; two others at 7.59. From then until 8.30 many came. Twice in that time there were three or four at once. On the whole the Bats returned much earlier than last night, although there was no apparent difference in the atmospheric conditions.
Sept. 5th.—Another fine still evening; moonlight. Twenty-seven Bats left the den between 6.59 and 7.4. The first returned at 7.58, the second at 8.4. From then until 8.50 many returned, singly and by twos and threes. Others put in an appearance until 9.20, when I left, but there was a marked falling off in the frequency of the arrivals during the last half-hour.
It may be that the period of activity is not limited to a short vespertinal flight of from one to two hours, and that the Bats leave their den again before daylight; but I do not think so, and for this reason. A captive Noctule which I had for some weeks during the summer used to wake up between 7 and 8 o'clock in the evening, and become very active, climbing about the box in which it was confined, and squeaking vigorously. When, as sometimes happened, I was unable to feed it until two or three hours later, it relapsed into the lethargic sleep which characterizes Bats in the daytime, and I had to rouse it again by warming it in my hand.
Noctules scuffle and squeak for half an hour or more before leaving their dens in the evening, and this squeaking may be heard sometimes even at midday. In Alderley Park, at noon on July 15th, Bats, presumably of this species, were squeaking in a Woodpecker's hole in a tall beech, and during the morning of Aug. 5th the noise made by the Bats in the hollow Scotch fir on the Edge was very noticeable.
This species changes its feeding-grounds at different times of the year. For some weeks about midsummer Noctules may be counted by scores on almost any evening along the road which skirts the foot of Alderley Edge on the north, but in spring and late summer the Bats will be sought in vain at this place. Their presence or absence is no doubt determined by the distribution of the insects upon which they feed.
From the beech, whence I had watched the Noctules fly early in May, I obtained nineteen on the 8th of that month. Their den was in a hollow limb about forty feet from the ground. The cavity, between two and three feet in length, was dry and warm in its upper part, and impervious to wind and rain, whilst near the lower end egress was possible by several crevices and an old Woodpecker's hole. At 7.15, some three-quarters of an hour before their time of flight, the jarring of a ladder against the tree caused some of the Bats to squeak. When I broke away the dead wood, however, and exposed them to the daylight, they made no attempt to escape, but remained huddled together in a comatose condition in the upper part of the cavity, their low temperature during sleep being apparent when I handled them. As I detached them from the sides of their den, to which they clung tenaciously with their feet, hanging head downwards, one wakened sufficiently to escape. The others, placed in a linen bag, were transformed in a minute or two from cold inert creatures to a hot struggling mass. Of the nineteen Bats secured, all but three were males. The majority were liberated at once, and took wing with ease from the flat surface on which they were placed, I retained a couple, as did my friends Messrs. T.A. Coward and F.S. Graves, and we were thus able to check one another's observations on the actions of the Bats in captivity. This species takes kindly to confinement; one of the Bats, an old female, and the principal subject of the following notes, was at the end of eleven weeks in perfect health and condition. Of the other captives, one was accidentally poisoned, and four were released after a few days.
The Noctule, like other Bats in captivity, shows little inclination for flight, especially in an artificially lighted room, and, when it does take wing, frequently collides with the walls and furniture. A confined space is indeed unsuited to its bold and dashing flight, although in a darkened room it will remain on the wing for some time and avoid accidents. In walking—a captive Bat's usual mode of progression—the body is carried clear of the ground, and supported on the feet and wrists only. The tail is curved downwards and forwards, and the interfemoral membrane pressed against the belly. The fore limb is spread considerably, but the phalanges with their connecting wing-membrane are tightly closed and folded back along the lower arm. In ascending a curtain or picture-frame, the claws on the thumbs are brought into use, and the tail, instead of being curved beneath the body, is then extended backwards, with the tip pressed closely against the surface of the object up which the Bat is climbing. For the time being it is analogous to the stiffened retrices of a Woodpecker or Tree-Creeper.
Any instinctive dread which Bats may have of man disappears quickly in captivity, but the Noctule is exceptionally fearless. Within a few minutes of their capture, I took two of the Bats singly from among their struggling fellows in the bag, and, holding them in one hand, offered mealworms with the other. So cramped were they that they could not move their limbs, but they seized and devoured the insects with the utmost sang froid. On the same evening others were climbing about my arms and neck without any signs of fear; and the old female which I had for several weeks used habitually to clamber up my arm as it rested on the table, and snuggle against my neck.
Before settling down to sleep after it has fed, the Noctule, like other Bats, goes through a somewhat elaborate toilet. The wings and interfemoral membrane are thoroughly cleansed by licking, and the fur of the whole of the body is scrupulously combed, the sharp claws of the toes being well suited for the purpose. During the process the Bat frequently sucks its toes, the moisture serving doubtless to keep the beautiful golden fur sleek and clean. No one who has watched a Bat clean itself, as it hangs suspended first by one foot and then the other, can fail to be struck by the creature's suppleness and agility.
In another respect this species resembles all the Bats I have kept in captivity. It never attempts to pick up food which it has accidentally dropped. It is true that when running about the table a Bat may encounter a half-eaten moth or mealworm, which it will seize and devour, but this is tantamount to finding a fresh insect altogether. If, however, a fragment of beef or a decapitated moth is dropped, and lies on the table immediately beneath the Bat's nose, or if a partially devoured mealworm succeeds, by dint of its convulsive struggles, in escaping from the Bat's jaws, and instinctively makes for the darkness beneath its body or wings, the Bat makes no attempt to recover it. It usually turns its head from side to side, and then runs forward on the look-out for fresh prey. This failure to recover, or even search for, food which has been dropped is not due to any distaste on the Bat's part, for it will seize and devour the lost prey if it be proffered again. It seems to arise from the absence of any conception that food once dropped can be found again, and no doubt implies that Bats obtain, and have for an infinite number of generations obtained, all their food whilst on the wing. Even if this be so, it is still very curious that a Bat should be able to adapt itself at once to entirely new conditions, and take food readily whilst held in the hand, and yet after a captivity of nearly three months should persistently ignore palatable food which it has dropped, and which lies immediately beneath it.
Bats drink frequently. My captive Noctules sometimes lapped water from a saucer which stood on the table, but generally took the liquid from a camel's-hair pencil, either by lapping, or by taking the brush into their mouths and sucking it. Their food consisted of mealworms (the larvæ of a beetle, Tenebrio molitor), raw lean beef, and such moths, beetles, and other insects as I was able to procure. All food was thoroughly masticated by an extremely rapid movement of the jaws before it was swallowed. The wings of moths were generally consumed, but the horny elytra of large beetles were bitten off and allowed to fall as the insect disappeared in the Bat's mouth. Mealworms and small moths, as well as Cicindela campestris, and beetles of lesser size, were seized and eaten without any attempt to overcome their struggles. On the other hand, large moths, such as Xylophasia polyodon and Phlogophora meticulosa, were sometimes, and the powerful beetles Geotrupes stercorarius and Melolontha vulgaris always, thrust by the Bat into the pouch formed by the interfemoral membrane, in order to secure them effectually before they were eaten. A Cricket (Acheta domestica) offered to one of Mr. Coward's Bats was treated in this way, but Cockroaches (Blatta orientalis) were in some instances thrust into the pouch, and in others eaten without that preliminary. It should be remarked, however, that Cockroaches, despite their size, submitted very tamely to their fate. On no occasion was foot, carpus, or thumb used to secure or dismember prey.
The insects eaten by any creature in captivity cannot be taken as a criterion of its food in a free state, but it may be worth while to note that, in addition to the moths already mentioned, the following, among others, were readily taken by the Bats:—Mamestra persicaræ, Leucania pallens, Hepialus humuli, H. sylvinus, H. hectus, Rumia cratægata, Urapteryx sambucata, Odontopera bidentata, Fidonia atomaria, F. piniaria, and Amphidasis betularia. The Bats appeared to be unable to see food if held but little more than an inch in front of them, and this was the case in natural twilight, as well as in an artificially lighted room. It is therefore very doubtful whether, in a free state, they would avoid a distasteful moth because its nauseous properties were advertised by its warning colours.
That certain insects were distasteful was clearly shown by the behaviour of one of the Bats. It seized a moth (Euchelia jacobææ) from my fingers, but dropped it immediately, shaking its head from side to side in evident disgust. Taking the moth in my fingers, I offered it again to the Bat, which declined to touch it, I then held the moth with a pair of forceps, which I generally used in feeding the Bats, as being less susceptible to their sharp teeth than were my finger-tips, and which were intimately associated with food in their minds. The moth was seized at once, but dropped immediately with repeated signs of disgust, and I could not induce the Bat to take it a third time. On the two following evenings I offered it other moths of the same species, doing so before I gave it other food, in order to make sure that it was hungry, but it would not touch them, although it sniffed at them, and probably recalled their nauseous qualities by its sense of smell. On another occasion an example of Abraxas grossulariata was seized twice, and then dropped with every appearance of disgust, and I could not get the Bat to touch it again.
Two other moths (Spilosoma menthastri and S. lubricipeda) appear to be unpalatable, but in a lesser degree. The first time I offered the Bat a menthastri, it seized and ate it without evincing any distaste; but on the next day it dropped another moth of the same species immediately, and then treated a lubricipeda in the same fashion, although it was hungry at the time. On the following evening I again tried the Bat with a menthastri, but without success. Three days later, however, I induced it to eat single moths of both species, but it dropped them several times, and only ate them eventually after a good deal of pressure. From that time the Bat overcame its distaste for these moths in a large measure, for on a subsequent occasion it ate seven menthastri and two lubricipeda with apparent enjoyment, but refused a tenth moth, although it was still hungry, and eagerly seized and ate several mealworms and flies.
Both of Mr. Coward's Bats persistently refused to touch an Oil Beetle (Meloë sp.) which he offered to them.
- The Noctule, although probably common and generally distributed, has been recorded from but few Welsh localities. Mr. G.H. Caton-Haigh states that it is common in Merionethshire (Zool. 1887, p. 293). In May, 1898, I saw several flying above the Beaver's Pool, on the Conway, near Bettws-y-Coed. In August, 1895, Mr. T.A. Coward saw many at Nevin, Carnarvonshire. The Bats, which were flying low over the fields at the edge of the cliffs, appeared to be feeding on the winged males of a black ant.
- Cf. 'Zoologist,' 1895, p. 167.
- For a description of this habit, see 'Zoologist,' 1899, pp. 471–474.