Notes on the Behaviour of a Hibernating Noctule (Nyctalus noctula)

NOTES

ON

THE BEHAVIOUR

OF A

NOCTULE ( N Y C T A L U S THE

E A R L OF

HIBERNATING

NOCTULA)

CRANBROOK

A female noctule, captured in a mist net 23rd October, 1963, was kept in captivity during the following winter. The bat was adult and had bred in 1963 : when captured it weighed 28 gms. It quickly learned to take food from the hand but in the short tirrte available before it went into hibernation did not learn to take food from a dish. It was not possible therefore to leave food for the bat to find and eat if it awoke. It was looked at at intervals between dusk and 10.30 p.m. or so every evening : if it was awake it was taken out and fed by hand, if asleep it was assumed to be in hibernation. It was fed on meal worms, supplemented by housecrickets to give a more balanced diet. It was kept in a room the temperature öf which varied between 5° and 15°C. over the period, reaching the lower limit only on a few occasions when the window was left open overnight.

Behaviour of a sleeping bat in Summer time During the summer noctules in the wild feed for about an hour or an hour and a half at sundown and for another similar period before dawn. A captive noctule follows a similar regimen : it will wake and feed at nightfall and then go to sleep, to wake later on and feed again. When not feeding or grooming itself it sleeps and when asleep the body temperature drops, the bat feels cold to the hand and is more or less comatose. Nevertheless the animal is not apparently completely unconscious. A sleeping bat hangs from the claws of its hind feet with the hind limbs extended.

If disturbed it raises the body by bending the limb joints and turns its head towards the disturbance ; if one side of its Container is tapped or scratched and then the other it will turn its head to the first and then to the second point of disturbance. It cannot though crawl away or take flight : if taken from its cage and dropped it falls to the ground with unopened or at most partially opened wings. In other respects too a sleeping bat's physical reactions are limited : it seems to maintain or at least quickly to regain its mental powers but does not regain its physical ones until it has warmed up. If picked up when still cold a freshly caught bat will cry out, try to escape and even to bite, the cries being less frequent and the struggling and biting less violent than in the same animal when fully awake. A tarne bat will open its mouth and seize a proffered meal worm but then merely holds the meal worm in its mouth and cannot apparently chew it up. In fact the general impression given is that of a human being in a nightmare, trying to escape from some imminent danger with limbs that refuse to move.

HIBERNATING

NOCTULE

447

Gradually though the bat wakes up and struggles more violently or suddenly starts to eat the meal worm in its mouth—it will then feel warm to the hand. Waking and warming up once started, whether by day or by night, seem to continue until the bat has regained its fßll powers : if thoroughly disturbed a sleeping bat will always wake and look for food and drink if accustomed to captivity or seek a way of escape if freshly caught.

Behaviour of hibernating bat Though the temperature of the room in which the bat was kept was no colder than it has been with other bats sleeping there on summer nights, the sleep of hibernation was much deeper than the ordinary sleep of Summer time. If the side of the case was tapped the bat drew itself up by bending its knees and brought its forearms close to its body but did not turn its head. If taken out and held in the hand its reactions were negligible and it took no notice of a meal worm even if put into its mouth. If then quickly replaced in its cage it remained cold and comatose and there was no further wakening or warming up.

Onset and course of hibernation T h e bat was captured while feeding 22nd October and for the next week behaved like any captive noctule does in the Summer time, waking at sundown or soon after and feeding greedily. On 29th October it did not wake, remaining cold and comatose, but woke again 30th and 3 Ist October at the normal time to feed as before. It did not wake Ist, 2nd, 3rd November but on 4th November seemed to be waking and was taken out and offered some meal worms. These it took and ate without much enthusiasm and could not be persuaded to take more than eight or ten : a noctule will normally eat 20 or 30 meal worms and will then take more if offered. That was the pattern throughout November : the bat would remain comatose for three or four days, wake, and if fed, feed rather half heartedly and then sleep for a few more days before waking again. By the beginning of December it was in hibernation.

It woke and fed half heartedly 15th and 30th December, 9th, 25th and 28th January, weighing 25 gms. before being fed 30th December, 24 gms. 25th January. T h e same pattern of behaviour was followed throughout the first half of February, the bat waking to feed on 4th, lOth and 15th February.

For the next three days it woke and fed every evening but remained cold and comatose 19th, 20th, 21st February, waking to feed on 22nd February when it weighed 20 gms. Thereafter it woke every evening and fed greedily until 4th March when unfortunately it escaped from its Container and could not be found. Throughout the period 22nd February to 4th March the bat's sleep was like the sleep of Summer time as described above : hibernation was obviously over.