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BAT TALK

The Bat Talk was first introduced by Maxcence Gross (R.N, March

-August '98) who studied bat diversity here using mist-netting techniques

(see report in the R.N. Library).

The talk outlined here is basically his, with a few embellishments of my

own, and this sheet should allow the talk to be given to interested tourists

by a willing R.N. The talk utilizes the bat board, currently in the museum,

which illustrates various bat feeding guides.

(Incidentally the mist net remains in the R.N. bungalow, although it is in

bad shape. Mist-netting requires trained and experienced researchers to

untangle trapped bats and birds).

Matt Waldram

(R.N.April-Nov.98).

INTRODUCTION:

Bats are the only truly flying mammal (contrast powered flight as opposed

to gliding flight as in honey gliders). They are important animals in the

forest ecosystem where they compromise 39% of all neotropical mammals.

They are the second largest order of mammals (behind rodents) worldwide.

Despite this, there is relatively little known about bats due to their nocturnal

flying. Hence there are many insights, misconceptions and untruths

about bats.

FLIGHT:

Adaption of the pentadactyl limb plan-thumb free of wing as a claw, other

four fingers greatly extended, (this is well illustrated in the central diagramon the board). The Latin name of the bats (chiroptera) literally means

handwing. Stretched between the fingers is a membrane which has many

special properties. Firstly it is alive, containing blood vessels, and will

heal if punctured or torn. It is soft and strong and elastic (i.e. doesn't

wrinkle when the wings are closed) but is easy to open (unlike elastic) as

the fingers are very thin and weak.

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The flight mechanism is different from that of birds, who have a basic

up/down flapping flight. Bats whose wings are impermeable to air flow,

must 'scoop' up the air by flapping in a 'figure-of-eight" pattern.

ECHOLOCATION:

Ultrasonic noises (best described as clicks) are emitted through the mouth

and nose. A picture of the environment is built up by listening for the echo.

The emitted sound is so loud that bats have evolved a way of disconnecting

the ear drum to prevent it being damaged. It is re-connected in time to hear

the echo and this can be done many times a second.

Bats have a very good spatial memory and when flying along well known

routes will only occasionally echo-locate in order to check their position.

Hence if a foreign object appears in a regular flight path (e.g. human on apath) the bat through negligence may brush past the object. This may be

the origin of the rumour that bats get tangled up in peoples hair, an action

that could in no way benefit the bat.

When bats close in on prey, they will increase the rate and frequency of

calls and this in effect increases the resolution of their echolocation

image. Bats are however not blind (another popular misconception) but use

their eyesight in conjunction with their echolocation sight - important

particularly for locating flowers for nectar eating bats. Bat flowers arenormally large and light colored in order to stand out at night.

DIET:

In Europe and other temperate regions bats are almost universally

insectivorous. However there has been a diversification of feeding

strategies in the tropics and these can be broadly grouped into 6

categories (which are illustrated on the board).

Nectar feeding bats (F. Glossophaginae): they have a long tongueand the ability to hover. Very important pollinators filling an equivalent

(but nocturnal niche) to humming birds, a niche they share with many

moths.

Fish eating bats (F. Noctihonidae/ bulldog bats): they go

fishing over still or slow moving water. Excellent echolocation enables

them to detect ripples created by fish near the waters surface, which

they catch by trailing oversized claws across the surface, like grapping

hooks. Catch fish up to 8cm.

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Vampire bats (F. Desmodontinae): true vampire bats, only 3

species in the world. Locally we have 2 of those which feed solely on bird

blood. These bats have enlarged forward pointing incisors which they use

to make an incision in their prey with. They then lap up the blood flow, the

saliva containing an anti-coagulant to keep the blood flowing (the large

incisors and sucking of popular vampires are again a myth). Vampire

bats have large thumbs and are good walkers on the ground, they canfeed on cattle and weaken them, although they would have originally

fed on tapirs and other large mammals. Through peoples ignorance

these bats are largely responsible for their general bad name (many locals

think all bats are "vampyros" and will kill them).

Specialized insectivore bats (F. Vespertilionidae): very

common worldwide. Evolutionary arms race with moths, some species

of which will stop flying and drop when they detect bats echolocation

checks. Specialized insectivores counter this by having an extended tailmembrane which acts as a "scoop" to catch the moth/other insect which

is then transferred to the bats mouth.

Carnivorous bats (some members of the Phyllostominae

particularly Trachups species): these are fringe lipped and will

feed on lizards, birds, mice and frogs. Large size (50cm.

wingspan). They home in on frog choruses and can

differentiate toxic from less toxic species. Another predator/

prey arms race is apparent when listening to frogs calling at

Laguna Chica. Frogs there will call intensively for 30-40 secs,

before being silent for 3-4 mins, an adaption to confuse bat

predators.

Fruit-eating bats (S.E. Cardlinae & S.F. Phyllostaminae): very

important as seed dispersers. A good example is the

Cardliaperspiculata, which feeds on the vertical fruits of the piper

plant (also Cecropia trees). Bats will fly over open areas (tree

foils, farm clearings, etc.) thus dispersing seeds into these areas

and helping speed regeneration. These bats possess a nose-leaf: afleshy protuberance over the nose - which acts like a megaphone

to focus and direct echolocation noises.

Another popular misconception is that bats are "flying mice". They are

actually thought to be evolved from shrews. The megachiroptera (flying

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axes) which are found in Asia, Africa and Australia are thought to be

separately evolved from animals related to monkeys. In contrast to the

microchiroptera, they have a second claw on the wing and no tail

membrane. So bats have many benefits including limiting the number of

insects and increasing pollination and seed dispersal.

The following points are usually made while showing tourists a live

bat. Again mist-netting and handling of live bats should only be

done by experienced persons. If no bat show is happening then these

points could easily be put into the talk.

Bats spend a significant proportion of their lives upside-down whilst

roosting during the day and they show many adaptions for this. The claws

on their feet are naturally closed, i.e., a muscle must be contracted to release

the grip so the bat can hang for many hours without suffering fatigue. Thisis similar to another upside-down animal, the sloth, and both will continue

to hang for some time after death.

The claws and knees also face backwards enabling the bat to rest with its

face towards a trunk or wall. This is important as the bat can fall straight

into flight rather than having to do a 180degree barrel roll! The upside

down position has also had an effect on toilet habitats, bats will actually

change position to "head-up" in order to go to the toilet (clever bats do so

when they are flying!).

When the young are born they are caught in the wings. The females have

teats in their armpits and will leave young together whilst feeding. The

mother will return several times a night to feed her young.

Useful references: Neotropical Mammals - L. Emmons.

Bats in Question - Wilson.

(both in R.N. Library)