Roosting Preferences of a Whiskered Bat

ROOSTING PREFERENCES OF A WHISKERED BAT (.MYOTIS MYSTACINUS KĂźhl) IN CAPTIVITY by

LORD

CRANBROOK

BATS when roosting or hibernating secrete themselves in a diversity of places, hollow trees, caves, houses, etc., and when in the roost or hibernacle will either hang free from the roof, against the sides or climb into cracks and crevices. Some species, e.g., the horse-shoe bats, almost always hang freely suspended from the roof, others are found sometimes hanging free, sometimes against the sides and sometimes in crevices. When hanging free or against the sides the bats hang by the claws of the hind feet and hang head downwards. In crevices they are found with the body at all angles depending on the shape, etc., of thecrevice. Oneof the bats which is found hanging up in such a diversity of situations is the Whiskered bat (Myotis mystacinus KĂźhl) and in 1960 one of these was kept in cages with a variety of alternative roosting sites to see if it showed any marked preferences. T h e bat was thoroughly accustomed to captivity and would feed and water itself. A ration of meal worms and /or blow fly pupae was placed in the feeding dish soon after dark and later, when the bat had fed and gone back to roost, more food was put in which was usually eaten by the morning. Water was constantly available in a shallow dish and the bat drank copiously.

T h e cage used was a wooden box 120 X 150 X 220 mm. high the walls of rough wood easily climbed by a bat. For three nights the bat was in this box hanging up each night on the walls. On the fourth day at the top of the back wall two sheets of glass 90 mm. deep and 75 mm. wide were fixed to form two separate vertical crevices with a partition between them. T h e bat could not pass from one to the other without climbing down out of one and then up into the other. T h e sheets of glass were interchangeable and were first fixed 10 mm. from the back. On the two following nights the bat hung up behind the glass, in the third night in the open on a wall. It was obviously rather cramped and had difficulty in grooming itself so the distance between the glass and the wall was increased to about 20 m m . and thereafter it almost invariably, slept in one or other of the two vertical crevices. With the glass at 20 mm. from the wall the hairs of the lower part of the bat's back were just touching the glass when it was asleep. (The hair of a whiskered bat is long and stands well out from the body while the bat arches its back slightly when hanging up.)

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ROOSTING PREFERENCES OF A WHISKERED BAT

Having accustomed the bat to roosting in these vertical crevices one of the sheets of glass was covered on the outside with black enamel, the bat side of both being still piain glass. The bat showed no preference as between piain or dark glass. If it hung up under the piain glass and the dark was substituted it was in the same place in the morning and vice versa, this substitution being made as often when it was hanging in one of the crevices or in the other so that there was no question of " crevice preference " affecting the result. In fact such crevice preference as appeared seemed to be purely conservative. T h e bat would sleep in the left-hand crevice, go down to feed, return and stay there whether under dark or clear glass only to do the same if removed and put under the right-hand one.

Light seemed to make no difference. On two nights in each of the two crevices under clear glass and with dark glass on the other the bat was left with a 60 watt lamp shining on it from a distance of 18". In every case the bat was found still under the clear glass in the morning, having certainly gone down to feed on two of the nights, when it emptied its food dish.

T h e other cage used was a box 200 X 250 X 250 mm. high.

T h e door was ]" wire netting boarded on the outside to prevent draughts, the sides of wood too smooth for a bat to climb. There was a false back, triangular in horizontal cross section and 10 mm. shorter in height than the true back. There was therefore at the top of the false back a horizontal crevice 10 mm. deep and, due to the triangular cross section, varying in width from 5 to 35 mm.

In front of the upper part of the false back was fixed, from side to side and parallel with the true back, a sheet of glass 100 mm. deep making, below the horizontal one, a vertical crevice 90 mm. deep and varying in width from front to back between 0 and 30 mm.

T h e false back was faced with perforated zinc to make a uniform and easily climbing surface. The bat therefore had a number of alternative roosting sites :— 1. Hanging vertically on the wire netting front, either against the boards or in a free draught.

2. Hanging in a vertical crevice of varying widths or on the back in the open below the crevice.

3. Creeping into a horizontal crevice of varying widths but uniform depth.

When first introduced into the cage the bat rapidly explored it throughout, pressing into the narrowest parts of both the horizontal and vertical crevices. It would do the same when re-introduced after spending a night or two in another cage. When thoroughly at home however it settled down into pretty regulär roosting habits.

ROOSTING PREFERENCES OF A WHISKERED BAT

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The most commonly used roosting site was in the vertical crevice at a point where the glass was 15—20 mm. from the zinc.

The bat never pressed itself into the narrower part of the crevice and only occasionally was it found in the morning in the wider part where the hairs did not touch* the glass.

It would sometimes hang on the door for part of the night.

On two occasions having spent the previous night in the usual place it fed at about 6 p.m. and hung up on the door. Düring the night it fed again and was found in the morning back in the vertical crevice. One morning it was found hanging on the door but returned to its normal roost after feeding that evening. It never slept on the back below the sheet of glass though it would occasionally hang there to groom itself. After seizing a particularly large and lively meal worm it would often hurry to the back wall and climb up an inch or two head uppermost to adjust its prey agäinst its belly. On a number of occasions it dropped the meal worm into the interfemoral pouch but seemed unable to recover it. The bat then turned head downwards and climbed down back into the feeding dish while the meal worm feil out onto the floor. It was not to be expected that the bat would sleep on the lower part of the back wall. Bats, in captivity at least, always climb as high as they can before roosting. If given, e.g., a wooden wall rough below and smooth above, a bat will climb as high as it can, feel desperately for footholds on the upper smooth part and take time to settle down half way up the wall.

The bat was never seen in the horizontal crevice save when newly introduced as described above.

After 3 weeks a piece of perforated zinc was fixed to one side wall continuing at right angles across the roof thus giving the bat the opportunity to hang at the top of a bare vertical wall or freely from the roof. It occasionally climbed up the wall a few inches, moved across on to the back and then went to roost in its usual place but never slept on the bare wall or roof.

SüMMARY.

A whiskered bat given the opportunity of roosting in a vertical crevice, a horizontal crevice, a bare wall or hanging freely from the roof showed a strong preference for the first. In a crevice of varying widths it chose a place where the tips of the hairs on its back just touched the surface behind it and did not appear to mind whether it roosted in darkness or light: touch seemed to be the deciding factor.