September’s harvest moon rose gracefully over the far side of Home Marsh, a pale orb of glowing white elegantly climbing over the reedbed. Its eerie light reflected down to cast a ghostly atmosphere over a subdued fen. A light breeze caused the silhouettes of Willows and Alders to sway as spooky giants over dewy grass paths that glistened with beads of moisture…
From afar, the “twit-twooing” of the Tawny Owls punctured the damp air; at first distant and soothing, swiftly becoming more hysterical as males vocally sparred to iron out there territorial boundaries. Somewhere out in the wilderness a Chinese Water Deer added its voice to the night, a short bark repeated slowly, but going unanswered.
However, much stranger noises echoed around the fen that night; the sound of multiple bat detectors translating the echolocations of nocturnally flying mammals so we ground-dwellers can hear them. From the smallest to the largest, the clicks and buzzes of Common Pipistrelles at 45khz mingled with the pops and squeaks of the much larger Noctules at 20khz. Of course, without the bat detectors we would be hearing nothing but the sounds of the fen, as most bat noises are beyond human hearing – except for those lucky few who might just make out a few squeaks. Alas, the natural aging process alongside overuse of the chainsaw at a young age leaves me struggling to hear the sounds of the bats these days, praise for the bat detector that unlocks the secrets of the night.
Even with the light of the moon, little could be seen but the odd glimpse of these speedy aerobatic marvels zipping around in search of their prey, we really were “as blind as a bat”. Although we know bats are actually far from blind, and can see roughly as well as we can at night. But that is why their echolocation is so vital for finding food and generally navigating around at such speeds without crashing into things constantly. Bat echolocation in a nutshell works by the bat sending out sound waves through its mouth (or nose, for some species). When the sound waves hit an object, be it a flying insect or a tree, the sound waves echo back to be picked up and analysed by the bat. This all happens in a split second, building a picture as good as any daylight display for the bat. Perhaps we should change the saying to “as blind as a bat when its echolocation is not working and it has its eyes shut” although I don’t think it will take off somehow, not as catchy.
The bats certainly proved they were better equipped for their night time travels than us humans, as a large group of us eager bat-watchers tiptoed carefully around the fen, the beams of torches illuminating the paths and more importantly, dyke edges. Around Wheatfen there is ample habitat for bats to thrive, with many dead trees left standing to provide a home for the bats in cracks, rot pockets, woodpecker holes and even under peeling bark, with larders of food in abundance – especially moths, as we demonstrated at the moth event last month. It is Ted Ellis’s legacy continuing, leaving the woodland wild and natural, not tidying up every dead tree and twig. Thus it becomes a haven for many species, including the bats.
Along woodland paths we crept, under the dark canopies of mighty oaks, now slowly shutting down for their winter sleep, but ever the watchful guardians of the night. The grand finale unfolded by the Thatched Hide. The pond was shrouded in a thin mist that gentled swirled, wraith-like over its surface, the water gleaming white under the moon’s incessant gaze. And out of the gloom came bats in great numbers.
We spectators gawped in wonderment as Daubenton’s bats sliced through the mist like fighter jets, as nimble as a dragonfly despite being far larger, expertly catching prey in flight, even gleaning insects off the water’s surface. Although this natural phenomenon was a delight to watch on such an atmospheric night, there was one more tool in our already extensive arsenal of bat detecting equipment. Thermal imaging cameras, mounted on tripods around the pond provided a whole different vision of the night and its nocturnal animals. Looking through the eye piece, guests on the far side of the pond suddenly glowed hot white as the heat emitted from them provided a crisp outline against the colder surrounding air. Even trees shone white, their bark still holding some heat from the day’s sun. And of course, those with a swift hand could follow the speedy bats around the pond, their small dark bodies suddenly becoming shiningly obvious, exposed through the cameras.
Overall, the evening was fruitful and a multitude of bats were glimpsed or heard on the detectors, comprising a total of at least 6 different species: Common and Soprano Pipistrelles, Noctule, Brown Long-Eared bat, Serotine and Daubenton’s bat. We would like to give a big thank you to Mary Goddard of Wild Frontier Ecology Ltd for leading the bat walk and for lending us the bat detecting equipment. You can also read more about bat watching in Norwich and Norfolk on the Norwich Bat Group website.