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Thursday, Sept. 5, 2002
GREAT NIGHT HUNTERS
One bat in the hand is worth flocks in the forest
By MARK BRAZIL
Science sometimes moves forward by exceedingly small increments, yet to be involved in making one of those tiny steps can nonetheless be extremely exciting, as it was for me early this summer.
It was a warm calm evening, though an occasional zephyr rustled the forest leaves and at times it felt as if a breeze might spring up. Almost any wind would have reduced the chances of our three-person team catching bats, as we were trying to do.
Surprisingly, little is known about bats in Japan, and it seems that no one has previously investigated those inhabiting the large lowland Nopporo Forest on the outskirts of Sapporo. In fact only one bat specimen has ever been reported from there, and that was of a common species known locally as kotengu-komori. These insectivorous creatures are hibernators, and the forest no doubt offers them plenty of cavities beneath bark, in rotted trunks and branches, and in old woodpecker nesting holes where they can shelter during daytime and then survive the winter.
Watching bats is nothing if not tantalizing, unless you happen to know where their day roost is. As darkness falls, these small creatures emerge silently and take to the wing, flitting erratically and at high speed, yet with astonishing control, between the branches. It is impossible to follow them by torchlight because they move so quickly, so spotting them means relying on peripheral vision -- that portion of our sight best adapted to low light levels and movement -- but that means never getting a clear view.
Modern technology helps. A pocket-size, battery-powered bat-detector is a device that converts inaudible bat vocalizations down to a frequency audible to the human ear. Point the detector skyward, and if there's a bat about, it emits a rapid series of staccato clicks.
At times the clicks accelerate, turning into a trill of sound. This may indicate when a bat has switched from its standard form of echolocation -- beaming out a stream of slow clicks that allow it to build a soundscape and "feel" its way around -- to its hunting frequency. Once it has "sighted" prey on its mental radar, it then switches to emitting this stream of more rapid high-frequency sound pulses that enable it to home in on its airborne prey.
Of course, echolocation also enables bats to identify barriers across their line of movement, particularly if the wind moves around a deliberately fine barrier like our soft nylon nets. But catching bats is a labor of love, what with the hours spent obtaining permission, buying banding equipment, preparing poles and nets and guying them in place in what seems a suitable spot.
Then there's the waiting -- for hour after hour. The waiting, and worrying, is the worst part, because after all that effort it only needs a breeze to billow around our nets and almost certainly make them plain to even the blindest bat's radar. Then again, even if there is no wind, bat-hunters worry whether there will be sufficient food about for their prey to hunt that night.
Anyone who has watched bird-banding operations knows that birds, unable to see fine nets, fly into them, fall into the nets' soft shelves, become entangled and then hang there passively. Naively I assumed that bat-banding would be the same. However, bats neither think nor act like their fellow fliers. Leave a bird alone in a net, and at worst it will become increasingly entangled; leave a bat alone in a net, I discovered, and it will promptly chew its way to freedom. On reflection, that makes sense, as spider webs must be a regular hazard for them -- and three gaping holes in our nets testified to the speed at which they can be rid of even monofilament nylon nets.
That evening, Hokkaido brown frogs were calling madly, which I took to be a good sign. Lots of noisy frogs meant the close proximity of water, little wind, and therefore surely lots of insects. There had to be bats, too, I reasoned. We opened the nets, six of them, strung along and across the forest trails, and waited at our base camp -- a little heap of bat-banding equipment, waterproof clothing and snacks at a fork in the track.
We sat and munched on our bento, hoping against hope for beginner's luck. Bat researchers often wait by their nets for many an evening catching nothing but a chill. Suddenly, though, our bat-detector stuttered. We caught glimpses of tiny forms flittering over us and around us -- forms that, since the one bat specimen ever recovered (dead) from Nopporo Forest had been a kotengu-komori, we took to be such. But would we catch one?
As we walked the trails to our traps, the bat-detector continued to utter its little rips of sound, stuttering out the beat of the echolocating bats above us. As we approached our most distant net we flashed a light along it and there, hanging in the folds, was a tiny shape -- we had scored. It could only have been there a few minutes, yet already it had almost chewed itself free -- and there were two other holes indicating we had missed more.
A tiny, tiny step on the long march of science, but this was nonetheless the first bat ever caught in the forest -- and for us it was as exhilarating as reaching a mountain peak. After drawing a blank with all the other nets, we returned to base camp and began processing "our" bat.
Measured, weighed, examined closely in the hand, it began to give up its tiny secrets. The lack of fur down the length of its tail gave us the biggest thrill of the evening -- this was no kotengu-komori. We had just caught a new species for the area. Reference texts showed us we had snared one of two species of hohige-komori (mouse-eared bat) belonging to the genus Myotis -- a first for the Nopporo Forest.
However, closer perusal of our reference works boded ill for our trailblazing captive. That was because the only way to distinguish these two mouse-eared species is, it seems, by killing the individual and then making detailed measurements of its skull.
It was then that we decided, in a less-than-scientific way, that as we had enjoyed beginner's luck in catching a bat at our first attempt, it, too, should enjoy the same luck and survive. We placed a tiny numbered band on one of its wings and offered it freedom. It sat on the outstretched hand it had bitten earlier, looked around, chattered to us via the bat-detector, then fluttered off into the darkness.
Though the nets remained empty for the rest of the evening, that one little Myotis bat (of whichever species) had provided us with a memorable and exciting adventure.