84) Microbat

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