The
name of the Bat with Long Ears is an understatement: the ears are huge almost
as long as the rest of the body and they play a vital role in the detection of
prey. Of all the British bats, the long-eared is the most distinctive. No
other mammal has ears that are nearly as long as its body. In fact, the ears of
the long-eared bat are so big that they can often be seen even when it is in
flight making identification easy. With its long, soft fur, large eyes and
delicate wings, it is a quiet attractive mammal with inoffensive habits.
Echo location!
A Bat with Long Ears finds its way about in the dark by means of echo location.
It emits high intensity, ultrasonic sounds (too high-pitched for us to hear).
Which are reflected from objects in its path? From the patterns of the
remaining echoes the bat can interpret its surroundings and avoid flying into
obstacles.
The
same mechanism is used to catch insect prey. Echoes bounce off even the
smallest midge and alert the bat to the presence of a potential meal. All
British bats are capable of intercepting flying insects in this way, and
probably compete for similar prey. But this leaves a whole range of suitable
food items untouched the insects, caterpillars and spiders.
Which
do not fly but crawl about among tree-top vegetation instead? Most bats fly too
fast to notice these creatures, and in any case probably cannot differentiate
between the echo of, say, a caterpillar and the leaf on which it is resting.
This
is where the long-eared bat comes into its own. Instead of emitting loud echo
location sounds which just bounce off foliage indiscriminately, this bat
whispers. Its ultrasonic noises are so quiet and sensitive that it can tell the
difference between an echo from an insect and what it is sitting on. The huge
ears detect these minute echoes, and also
The
Bat with Long Ears is a nocturnal mammal, foraging by night. In flight the
sensitive ears are held erect, directed forwards so they can detect insect prey
by echo location. When the bat is at rest or crawling about, the ears crinkle
along their outer edges and are then lowered over the shoulders.
There
are two long-eared bats in Britain, the common and the grey. The grey (Plecotus
austriacus) is very difficult to distinguish from the common and there are no
external features which provide positive identification of every specimen.
Generally
speaking the grey long-eared bat has darker fur than the common, which is
browner. The presence of the grey was overlooked in Britain until 1963, and
even now little is known about it. So far it has been identified only in
southern England, though it may be more widespread.
Distinguish
between sounds reflected from different textures, such as a soft insect larva
and a smooth leaf. The sounds are made and the echoes interpreted in a split
second during flight a remarkable feat since it involves only part of the bat's
brain, the whole of which is smaller than a pea.
Foraging! The
task of catching insects is made easier for the long-eared bat by its ability
to hover at an angle of 300. The long-eared bat can pick food delicately and
precisely off foliage and bark, and perhaps even from the ground. As well as
the usual flying insects, its diet therefore includes a whole range of
invertebrates gleaned from trees which other bats do not manage to exploit.
In
late summer especially, the Bat with Long Ears takes large numbers of noctuid
moths, snapped up on the wing and carried off to a convenient perch to be
dismembered and eaten. Usually the moth wings and legs are discarded, and a
little heap of such litter accumulates below the perch.
Attic Nurseries
The
Bat with Long Ears habit of using feeding roosts near human habitation, and its
ability to hover and fly in confined spaces make it likely to be one of the
species that flies into bedrooms at night through open windows. It is difficult
to be more precise since few people favored by such a visit stop to check the
identity of the intruder.
The
Bat with Long Ears mostly roosts in attics. Groups of up to two dozen females
gather in attics in summer to bear their young. They are usually so quiet that
they easily pass un-noticed by the householder, and can raise their young
undisturbed. Attics make good bat nurseries because they are warm. Higher
temperatures mean faster growth and development for the young.
On
cool days the bats huddle together to warm their offspring. Such a colony does
no harm, and may help to keep the roof space clear of moths, spiders and
destructive beetles. The young are born in June and July. Each female never has
more than one baby a year and none at all in some years. The population thus
increases only slowly. When a colony is wiped out it may take a decade to
recoup.
A
low breeding rate is characteristic of bats probably because their babies are
so big. Each weighs nearly a third as much as its mother at birth. Under
natural conditions bats do not need to produce large numbers of offspring as
they have few predators to Fear. The long-eared, For example, is occasionally
taken by owls and cats, but is otherwise safe except from destruction by
humans.
Adult
males do not usually roost with nursing females, and take no part in rearing
the young. They meet up with the females again once the young have been weaned
and the nursery colony has dispersed for the winter.
Three-month hibernation
like other insectivorous animals, the long-eared bat faces a critical shortage
of food once the colder nights of autumn begin. Two options are open to it.
Either they flying south to warmer places, or staying put and drastically
reducing energy requirements by hibernating.
It
seems that Bat with Long Ears normally hibernate, often staying close to where
they have spent the summer months. They usually hibernate in trees and
buildings; though sometimes use caves, mines and other similarly cool places.
Their preferred hibernating temperature is probably about 0°C (32°F).
Bat
with Long Ears would be forced into unnecessary and unwelcome activity if they
hibernated. Somewhere that became too warm on sunny winter days. Winter
activity is undesirable because there is little chance of recouping the fat
reserves used to provide energy for flight.
If
the bat finds a suitable place, it may well hibernate for over three months.
During hibernation the large ears pose a problem. Precarious moisture may
evaporate from their large surface and, even when this difficulty is avoided by
the choice of a cool, humid place to pass the winter, they a vulnerable to
frostbite.
The
ears could get in the way if the hat wanted to crawl into a more sheltered
crevice, so the problem is solved by folding the ears backwards. Hibernation
ends in March in the south of England, probably later in the north though this
varies with the prevailing weather.
Mating
takes place soon after hibernation ends or perhaps earlier during periods of
wakefulness in winter. When they wake up the hats start feeding to recoup the
.2O or more of lost weight.
Nocturnal Sorties
Long-eared
bats become active within the day roost at about sunset every night. They are
emerging from the nooks and crannies where they have passed the day. They may
spend up to an hour or so making short flights and grooming their silky fur. If
the long fine fur becomes matted, it loses its insulation, stream-lining and
rain-proofing properties. Once it is fully dark the hats go out to forage.
Sometimes
they stay out all night at other times especially if there is plenty of food
about. If there are babies to be fed they may return within the hour.
Perhaps they are making another sortie later. Long-eared bats normally manage
to find all the food they need without having to fly far from home.
Occasionally,
some Bat with Long Ears hats appear to make extensive journeys out to sea. They
have turned up among night-migrating birds attracted to offshore lighthouses,
in 1%8 one was found dead on a lightship in the North Sea, 31 miles out from
Great Yarmouth. Source: CP
