Microchiroptera
Three blocks from
my parents’ new house in the unfinished Canberra
suburb of Wright there’s a streetlight that rises above a roundabout like a
four-leaf clover. Four bulbs project
from the central stem and pour into the darkness a light that is of such
intensity that when you stand beneath the lights and look up towards them
everything beyond them vanishes. The streetlights that line the adjacent roads,
that illuminate the edges of the construction sites and empty houses, are dull
by comparison, and seem subordinate to the light above the roundabout.
In the way of Canberra, nearly 600
metres above sea-level, the nights are cool; but it’s summer, all the same, and
the days are warm and long; the mornings are gentle. Insects are hatching.
Beneath the streetlight above the roundabout near my parents’ new house Christmas
beetles (Anoplognathus
pallidicollis) are swarming in their hundreds.
Across the road
from the roundabout is a plantation of eucalypts – brittle gums, to be precise,
slender young trees with beautiful smooth bark. They’re planted on rutted,
muddy ground, and if you follow the mountain bike track that winds through them
you might before too long arrive at the ACT Bushfire Memorial: twelve years
ago, in another summer, the area which is now being redeveloped and built was
burned to ash in the Canberra bushfires of 2003, a cataclysm which killed four
people and destroyed 500 houses or more.
It burned out
miles of bush, too; the trees here are young. This landscape seems many years
away from providing refuge to wildlife – so many Australian birds and mammals
depending on the hollows of elderly trees in which to live and nest.
Yet there’s
wildlife here, the more adaptable animals settling as they do into disturbed
ground, making use of small niches. Walk
through the gums and you’ll see Superb Fairy-wrens (Malurus cyaneus), Yellow-rumped Thornbills (Acanthiza chrysorrhoa), Crimson Rosellas (Platycercus elegans). In the middle of a dam adjacent to the
brittle gum plantation there are currently a pair of Hoary-headed Grebes (Poliocephalus poliocephalus) nesting
atop a PVC pipe. On the grass between the gums and the Cotter Road there are scores of Eastern
Grey Kangaroos (Macropus giganteus).
And at night when the Christmas Beetles swarm beneath the lights, Bats emerge
from the night to feast upon them.
There are two
broad groups of bats, and beyond the superficial fact of both being flying
mammals they are so different that taxonomists have at times struggled to
elucidate their relationship to each-other. They have, certainly, been evolving
in separate directions for many millions of years. The most conspicuous of
these two groups are the Megaobats (Megachiroptera)
– the fruit-bats, or flying foxes, generally large and with excellent eyesight
and sense of smell. Yet when most people
think of bats it’s probably, unconsciously, a Microbat to which their mind
turns.
Microbats are the
gargoyle-faced animals, the tiny flitting things, the voracious carnivores, the
cave-dwellers that we learn at an early age to associate with the word “bat”. Overwhelmingly insectivorous – though not
universally – they have poor eyesight, tiny bodies (the smallest is just the
size of a person’s thumb; most you could hold easily in one cupped hand), and
an extraordinary way of perceiving their surroundings. Flight places great demands on an animal’s
metabolism, and bats have had perhaps 100 million fewer years of evolution than
birds, so while the White-striped Mastiff Bat (Tadarida australis) may weigh up to forty grams, the White-plumed
Honeyeater (Lichenostomus penicillatus), a bird of
similar or even slightly larger size, weighs only around twenty grams. Compared to other mammals bats have delicate
bones, but when it comes to flight they are not nearly as highly adapted as
birds; so they must compensate by consumption.
A bat in flight is
constantly feeding: a single Microbat can eat thousands of insects every night,
as much as half its own bodyweight. Such
activity requires the animal to have an acute perception of its surroundings –
and it’s this requirement which has led to the Microbat’s most distinctive
feature.
Microbats navigate
by echolocation. When humans developed
technology to allow us to do the same thing, we called it sonar. Sounds are emitted, and from the time at
which their echoes return to the source of the sound a picture of the landscape
is created. Bats call constantly and so
get a constant sense of the environment in which they fly – and by doing so they
are able to detect immediately even the slightest change in that
environment. Change such as the passage
of an insect through the air – and when a Microbat detects an insect its rate
of calling increases to an excited chatter, akin to a human opening his or her
eyes wide and staring straight at something that’s caught his or her attention.
Microbats in
popular culture are screeching, shrieking, chattering things – yet to the human
ear, the great majority of Microbats are silent. So much so that for the most part we don’t
even realise they’re among us: we may, if we’re lucky, glimpse a distant tiny
shape flitting around the crown of a tree at dusk, its flight not quite
bird-like; or we may see an animal just slightly too large to be a moth dart
through the lights at a sports stadium – but such sightings are fleeting, and
rare, so we don’t realise how full of life the night is.
Yet every night
when we walk the streets, everywhere on the planet except Antarctica,
we’re walking beneath a throng of bats.
If we could hear them it would change our perception of the world
utterly. But we can’t: human hearing is
limited, as all senses must be, and save for a handful of exceptions the
world’s approximately 1000 species of Microbat call at a frequency that is
beyond our ability to hear. Perhaps this
is for the best: the calls of some species can be louder than 100 decibels –
easily enough to drown out all other noise, were we able to hear it.
But – we can hear Microbats; because human
hearing may be limited, but human ingenuity is limitless. With a device called a bat detector, we can
tune into the sounds of bats that would otherwise be lost to us. We can listen to the night.
I first used a bat
detector more than a decade ago, when I was at university. I went on a week-long field trip to
Mulligan’s Flat, at the northern edge of the Australian Capital Territory, the purpose of
which was to survey animal and plant species of all kinds. One night we did a bat survey, and the
lecturer who was leading the field trip introduced us to bat detectors.
We walked a long
quadrant, tuning the detector, listening to it.
A bat detector is, in principle, simple: it has a microphone at one end,
which is sensitive to what in human terms we call ultrasonic frequencies; at the
other end is a speaker which broadcasts what the microphone picks up, but at
frequencies that humans are able to hear.
The workings of the machine are more complicated than that, but in
effect what the bat detector does is this: it hears bat calls and plays them
back so that we can hear them.
I used a bat
detector all those years ago, and yet I didn’t buy one until just over a month
ago. I’d been thinking about it for
years, I’d been circling the idea. I am,
often, extraordinarily slow to act. When
I ordered the bat detector – the simplest and cheapest model money can buy,
about a hundred Australian dollars and ordered from the UK – it arrived in only a week and
a half. The rest of the world does not
operate on my time scale.
The bat detector
has been revelatory. Standing beneath
that street light near my parents’ house I heard, night after night, as many as
half a dozen different species. The air
was filled with their calls, and I wondered why it had taken me so long to get
a bat detector after thinking about it for so many years.
But that’s been
the pattern of this year for me, more than most years: 2014 has been a year of
slow culminations and abrupt changes.
Getting the bat detector – and by now my friends and acquaintances,
though they politely say otherwise, must surely be sick of hearing me talk
about it; travelling around Victoria, my home state for this last decade though
I’ve never considered it as such; finally seeing my writing career start to
take off. Though December started with a
situation which seemed catastrophic at the time, and still sometimes does – a
situation in which I was partly culpable, and from which I cannot yet tell how
quickly I’ll recover – my year has nonetheless been overwhelmingly
positive. 2014 has been a good year.
Yet – the rest of
the world does not operate on my time scale, and nor does it accord to my
experience. By any measure which takes
in more than one person’s life this has been an awful year, a year filled with
a litany of disasters both ordinary and extraordinary which it will do no good
to repeat here. I’ve been aware as the
year has progressed, as one piece of personal good news has been shadowed by
more horror from Australia
or overseas, of a tension between my own life and the wider world. How does one reconcile that? How can we hold in our head an awareness of
the tragedy in the world, and still celebrate personal triumph? I’m not sure; except that we do. Except that I have.
The bats flew
around the street lights near my parents’ house again last night. I took my father up to see them. Through the bat detector their chatter
sounded like the crackle of distant fireworks; some time between ten PM and
midnight they descend from above the lights to below them, and my father and I
watched as one and then another and then another darted hard and fast and
straight through the dimness at the light’s periphery. I rejoiced in them; yet as I grinned at the
activity of the bats I was aware, too, of the insects being devoured in the
night, of the thousands of tiny deaths just above my head. When does an insect’s death begin to weigh on
us? When do we consider it of
consequence? Is there a number – 50
dead, 100 dead, 500 dead? Ah, but I was
here for the bats. I put it out of my
mind. It can seem callous, to so
selfishly ignore the calamity, but sometimes that’s all you can do.
Image sourced from http://en.wikipedia.org