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 wont care if they ever put up the cost of subs in future. Just think of the money youd 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.
Bats are found over the whole world except for the
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
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 mothers 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 bats presence.
As most of the bats 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
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.
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 Reads 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.
Friday. Ireby
Cavern/Dow Cave.
Saturday. G.G. via Disappointment, Bar or Main Shaft.
Sunday. 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.
May 1st. ST.
CUTHBERTS. MOCK RESCUE.
From Catgut Rift to High
Chamber. 2.30pm @ Belfry.
May 15th. ST.
CUTHBERTS. MOCK RESCUE.
From Pulpit Pitch. 2.30pm @ Belfry.
May 16th. STOKE LANE.
Meet at Stocks Farm 11am. Exposure suits advised.
May 30th. G.B.
Meet @ Belfry 11am.
June 4/6
Details later.
June 26th. ST.
CUTHBERTS. MOCK RESCUE.
Details later.
Cave Communications.
Since the meeting reported in last months 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.