The Belfry Bulletin
Number 205 1965
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Monthly Journal Of The Bristol Exploration Club
March Vol. XIX No.3
With the publication of the March B.B. actually in March (by one day!) we shall gradually get back to a normal date of appearance. We understand that the postal copies were a little late last month, but this was in some part due to the unavoidable absence of our “Postal Department” from their usual haunts. We welcome a change in the B.B. production arrangements which consists of a volunteer – ‘Kangy’ King, who has agreed to help the editor out by taking over the collating and stapling of the magazine, so with more than the usual amount of luck, a bigger and more regular B.B. may well result. By the way, we are getting short of articles of reasonable length and standard (gentle hint!) “Alfie” _______________________________________________________________________________________ In view of the earnest hope of the editor that the next B.B. (for April) will follow this one closely, most of the space in this B.B. is being taken up by a single article on Bats. It is some time since we have had an article on this aspect of caves, and whilst apologising to all bat-haters, we feel that this is a good opportunity to publish most of this article. The normal type of varied menu will (we hope) appear again next month. _______________________________________________________________________________________ WHY BOTHER TO PAY YOUR SUB EVERY YEAR?? A life membership only costs five guineas and then you won’t care if they ever put up the cost of subs in future. Just think of the money you’d save!! _______________________________________________________________________________________
BATS …..by R.E. Ball. When entering a cave, do you realise that you are invading the home of many living creatures? Life, though perhaps not obvious, abounds in most underground places and, whilst it takes many forms, the one most likely to be seen is the bat. This animal, a representation of which is, of course, the club emblem, is familiar to most cavers and in this article I hope to explain a little about the reasons for the presence of bats in caves and something about the general life of a bat. Caves and mines are used by some species of bat for the purpose of hibernation during a period of from about October to April. For the rest of the year, few bats are to be found in caves. Those that are, are usually found to be immature non-breeding individuals. Bats are mammals and collectively are called Chiroptera meaning ‘hand-winged’. They are classified into two orders Mega- and Micro-chiroptera. Megachiroptera comprises the large fruit bats of the tropics, while Microchiroptera contains mostly smaller insectivorous species and includes all the bats found in this country. A few bats of this second sub-order have developed rather odd tastes, we have all heard of the vampire bat which lives on animal blood, but few people know that some bats catch and eat fish as their principal food. All British bats are insectivorous so we have no need to fear of having our blood sucked when we enter Mendip caves! Sub order Microchiroptera has sixteen families, two of which are found in this country, these being Rhinolopidae and Verspertilionidae. The first family contains the horseshoe bats which are the most common in our caves and I will deal later with identifying these and the bats in the other family.
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Bats are found over the whole world except for the Arctic and Antarctic regions, although they are most abundant in the warm regions. Bats evolved early in the tree of life and fossil remains very similar to modern species have been found in Eocene deposits about sixty million years old in Darmstadt, Germany. They are thought to be distant relations of the order insectivore, which includes the shrews, moles, and hedgehogs, and to have commenced their evolution some hundred million years ago. The way in which the skeleton has become modified during evolution is remarkable. The upper limbs have developed greatly and the lower limbs degenerated as their use diminished. Across the shoulders, the bat is broad and powerfully built the rib cage and collar bones being large and strong to provide anchorage for the huge muscles needed for flight. The pelvis, on the other hand, is extremely narrow and light and the legs are slender with half turn twist so that they bend forwards at the knee. The feet have strong hooked claws and a powerful grip. The arms show the most amazing adaptation. The humerus is lengthened and the radius, lower arm, is enormous and as long as the body. These long bones of the arms and hand provide the framework over which is spread the membrane of skin which forms the wing. This membrane stretches from the fingers to the ankle and also fills the space between the legs with the tail helping to support this part of the wing. This membrane between the legs can be formed into a pouch during flight and used to catch and carry large insects, leaving the mouth free for further prey. The body is covered with fine silky hair which varies in colour depending upon the species. It is generally some shade of brown, ranging from pale fawn to a dark, almost black colour. They are, of course, warm blooded animals, giving birth to live young which are suckled by the female. Their breeding is interesting because in all British bats, each female produces one young per year, it takes two years for two young to be born to replace the parents. As the bat will be at least one year old before the first birth and two at least must be produced from then on to replace natural losses, it follows that the bat must live for about five years at least to avoid extinction of the species. In fact some bats live longer than this, and a lifespan of fifteen years is not considered unusual. Mating is entirely promiscuous and the male takes no part in the rearing of the young, in fact the two sexes live apart during the period from before the birth until the independent flying of the young. After leaving the caves, the breeding females congregate in the roofs of old buildings and form nursing colonies. Here the young are born late in June or early July. They are born blind and almost hairless and at birth are almost a third of their mother’s weight. Initially, the baby clings to the mother and is carried around by her on the nightly flights for food. The baby grows rapidly and soon becomes so heavy that the mother leaves it behind in the rafters to await her return. The young bat is able to fly by the fourth week and by the middle of August it is ready to face life on its own. By the autumn, the young have grown to adult size and are virtually indistinguishable form their parents. As already mentioned, all British bats are insectivorous and their food consists of flying insects such as moths, flies and beetles. The prey is caught in flight and the larger insects are often taken to a convenient spot where the bat can deal with them while resting. Under these places can be found considerable quantities of beetle shells and moth wings and these piles of remains are good clues of a bat’s presence. As most of the bat’s activity takes place at night or in dark places, it is obvious that some means other than sight must be used to enable them to fly and catch their food. As is now generally known, the bat employs a form of sonic echo location using sound waves of a frequency much higher than the human ear can detect. This was first suggested by Professor Hartridge in 1920 and confirmed later by Grif in Galambros in the U.S.A. The exact way the bat uses the sound pulses and reflected echoes to provide a sound picture of its surroundings is still a subject of scientific discussion and experiment. J.D. Pye of the British workers in this field has taken some interesting films which have recently been shown on television. The frequencies of sound used vary from 40 to 80 kilocycles per second. This compares with the 20 kilocycles per second which may just be heard by people with exceptionally good hearing in the upper register. As well as producing the echo locating pulses, the bat has a range of sounds we can hear. These are sometimes high pitch squeaks uttered in flight, which may themselves be close to the upper limit of audibility and are most likely to be heard by children. Other noises are described as buzzes and shrieks. These noises are probably a form of communication between individuals or to denote alarm or fright.
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As suitable food is scarce in the winter months, the bat is faced with the task of surviving this period with little food. The alternative solutions are migration or hibernation. At the moment the evidence points to the fact that some bats do normally migrate to the continent in the autumn, but we should like to learn much more before thinking we know the full story of migration. The great majority of bats hibernate and this is when they are to be found in our caves. Hibernation involves a slowing down of all bodily processes. Pulse rate and breathing slow down and the body temperature falls. The bat can now exist for a considerable period of time with the expenditure of very little energy. This is essential as, although a little food may be found at times, the bat has to exist almost entirely on the food stored as fat within its body. Hibernation is not complete however, and every few days the bat returns to an active state and undertakes a short flight in suitable weather conditions. Sometimes the bat may even fly outside the cave, or fly several miles to spend its next periods of sleep in a new locality. This type of movement can be traced by bat ringing schemes which will be mentioned later. There are fourteen species of British bat, of which about eight occur locally in significant numbers. Those most commonly seen in caves are the Greater and Lesser Horseshoe bats. These are distinctive in their resting position as they hang freely from the rock surface freely and cover their bodies completely with their wing membrane. In this position they hang looking like wizened rotting fruit. All other bats hide in crevices in the rock and are much more difficult to see. Greater Horseshoes have a wing span of about 14 inches and the Lesser Horseshoes about 9 inches. The weight is variable being greatest before hibernation and least in the spring. The range of weights is roughly for the Greater Horseshoe from 28 gram to 15 gram. (1oz down to ½oz) and for Lesser Horseshoes from 6 gram to 4.5 gram. There is a good deal of individual variation and in general females tend to be a little larger and heavier than the males. The information obtained by the bat through its ears must be extremely accurate, enabling it to fly with unerring accuracy though and round the passages in the cave and to fly without hesitation through small holes. When landing in pitch darkness, the bat chooses its exact spot and lands there feet first and head down, already in its upside down position. When disturbed during hibernation, the bat commences to awaken. This takes several minutes depending on the degree of torpidity at the time. When the bat is awake, it does not fly off immediately, but before launching itself, it spend a few minutes building up a picture of its surroundings. The head is moved from side to side emitting pulses in all directions, while the large ears are scanned rapidly around. When the bat has ‘seen’ what surrounds it, it drops off the wall and flies powerfully away. This awakening and flight involves expenditure of energy and the bat cannot let this happen too often during hibernation, hence, every time a bat is disturbed, its chances of surviving the winter are to some extent diminished. For this reason, I would appeal to all who meet bats in caves to disturb them as little as possible. Bats normally seek secluded places to avoid draughts and it is not normally necessary to approach too closely to a sleeping bat. Goatchurch is now devoid of bats owing to the many people using this cave and the numbers in Read’s Cavern have fallen recently as this cave is becoming more popular. The motto should always be “Let sleeping bats lie”. ___________________________ The remainder of the article will appear in the B.B. for April. Caving Meets. APRIL 16th – 19th. YORKSHIRE. Friday. Saturday. Sunday.
Ireby Cavern/Dow Cave. G.G. via Disappointment, Bar or Main Shaft. Alum Pot via Main Shaft or Long Churn Cavern. --------------------Camping at Flying Horseshoes, Clapham at 2/6 per person per night. Transport arrangements to be finalised at Club on Thursday. For further details contact Dave Irwin or Keith Franklin.
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May 1st. ST. CUTHBERT’S. MOCK RESCUE. From Catgut Rift to High Chamber. 2.30pm @ Belfry. May 15th. ST. CUTHBERT’S. MOCK RESCUE. From Pulpit Pitch. 2.30pm @ Belfry. May 16th. STOKE LANE. Meet at Stock’s Farm 11am. Exposure suits advised. May 30th. G.B. Meet @ Belfry 11am. June 4/6 DEVON. Details later. June 26th. ST. CUTHBERT’S. MOCK RESCUE. Details later. _______________________________________________________________________________________ Cave Communications. Since the meeting reported in last month’s B.B. we hear that most of the teams concerned are now actively engaged in designing and building equipment. “Sett” has also done a theoretical analysis based on propagation of radio waves under the conditions which will be met with, and this is being circulated. Interested people will be advised of the next get together and of further progress. _______________________________________________________________________________________ Personal. Congratulations to ‘Kangy’ King and Mrs. on the recent addition to their family, a son, Philip born 18th March and weighing 7lbs. Also to ‘Spike’ and better half (a trifle belatedly) on the birth of their daughter, Stacey Jane, on the 19th February. _______________________________________________________________________________________