Fre­quency FLY­ERS

As the sea­sons turn, and dusk ar­rives ear­lier, Matt Gaw tunes into na­tive bats at Knet­tishall Heath

EADT Suffolk - - Your Pictures -

THE barn owl ghosts over the river­side path just af­ter we set out, fly­ing low and silent over the long grass of the river­side meadow. I fol­low her with my binoc­u­lars, the gold of her wing and the chalky white­ness of her body bright against the dark­en­ing sky.

Along with about 20 other peo­ple, I’m here at Knet­tishall Heath to look and lis­ten for bats. The only mam­mal ca­pa­ble of true flight, bats are crea­tures of myth and magic, both ma­ligned and revered as a sym­bol of life and death, a to­ken of good for­tune and im­pend­ing doom. The su­per­sti­tion of the old world may have largely gone, chased into the light by sci­ence, and made car­toon­ish by Hal­loween and Hol­ly­wood, but the fas­ci­na­tion for this winged crea­ture of the night re­mains.

The owl dis­ap­pears. Sam Nor­ris, the ranger for Knet­tishall, and Mark Smith, from Suf­folk Bat Group, lead us on, a swish­ing conga train of cagoules and Goretex now walk­ing away from the river and to­wards the heath. All of us are car­ry­ing bat de­tec­tors, a hand-sized gizmo that trans­forms the in­audi­ble ul­tra­sonic calls of bats into a sound the hu­man ear can hear. I walk with it at head height to keep it away from the in­ter­fer­ence of my phone, lis­ten­ing to its white noise crackle. A light­ning rod for bat con­tact.

The de­tec­tors are set to 50kHz, a fre­quency that will cap­ture two of the most reg­u­larly heard bat calls, those of the com­mon and so­prano pip­istrelle. Back in the car park, Mark had told us that many bats will sweep through this fre­quency, it is then a ques­tion of tun­ing up or down to iden­tify the peak fre­quency at which the bat is call­ing.

The range cov­ered by bat calls can over­lap,

but the peak fre­quency can be cru­cial to species iden­ti­fi­ca­tion, from the low cas­tanet smacks of the bar­bastelle at around 36kHZ to the bub­bling call of the in­cred­i­bly rare lesser horse­shoe bat at 109kHz. The tone, rep­e­ti­tion and rhythm are all key too.

Mark also played us some record­ings of calls to demon­strate and help us iden­tify in the field – the pip­istrelle that he de­scribed as hav­ing a fast clip-clop-clip-clip-clop rhythm, while the noc­tule, Bri­tain’s largest bat, is louder and slower. Clip. Clop. Clip. Clop.

As we move from heath to wood pas­ture, one or two of the de­tec­tors pick some­thing up. A wet gal­lop­ing sound, like a high-speed heart­beat or the pulse of elec­tric­ity on rail tracks. A bat. But it’s gone al­most as soon as it ar­rives, leav­ing us with static and low con­ver­sa­tion.

We keep walk­ing. The light is re­ally go­ing now. Sucked into leaves, the gloom of the heath re­placed by night time tun­nels cre­ated by cor­ri­dors of birch and pine. It is in these shel­tered ar­eas that bats hunt. If the air hangs still so do the midges and flies, clus­ter­ing into smoky clumps that are easy tar­gets for the bats’ echolo­ca­tion.

Our group fans out, pick­ing their way through the trees, each per­son find­ing their own spot, the dark only bro­ken by a few wob­bling torch flashes.

The calls come grad­u­ally; first quiet and then grow­ing louder. There is more than one bat here. Mark thinks three, pos­si­bly four pip­istrelle. They aren’t fly­ing past but cir­cling around, pick­ing off moths and flies.

I re­tune my de­tec­tor slightly, the clip-clop rhythm of the com­mon pip­istrelle is there, a jow­elly wob­ble board of slurpy wet smacks. The calls get closer and closer to­gether as the bat gains on its prey. The chase ends in an elec­tronic rasp­berry – bat, ul­tra­sonic call and in­sect com­ing to­gether. Sup­per and death.

We walk from the wood back across the heath, the light from torches catch­ing the backs of the eyes of Ex­moor ponies that graze the heath. Asleep with their eyes open. Mark stops us one more time. He has picked up an­other bat. A so­prano pip­istrelle. Even smaller than its com­mon name­sake, its wing span be­tween just 192mm and 232mm, its call is higher, the ul­tra­sonic cries, sharper and closer to­gether to catch its tiny prey. For the first time tonight I can ac­tu­ally see it too. Its flight is fast and er­ratic, drop­ping out of the dark­ness like a shadow made solid. Flit­ting, dis­ap­pear­ing. An­other lit­tle bat joins it and they fly fear­lessly close to our heads.

To them we are no more than ob­sta­cles to be avoided, mov­ing non-foody lumps in a world of dark­ness and echoes.

‘A wet gal­lop­ing sound, like a high-speed heart­beat or the pulse of elec­tric­ity on rail tracks’

Pip­istrelle bat in flight. Photo: BCTRJ Brookes

Bri­tain’s largest bat, the noc­tule. Photo: Belizer adobe­stock

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