Daubenton Bat Photo Credit: Bev Mulcrone
Watching the swooping antics of bats in autumn is one of the UK's great wildlife spectacles, and one I look forward to every year. Their amazing skill in echolocation and agile flight are an absolute marvel to behold, and when I found out that there was a bat walk being held at Strumpshaw Fen, I couldn't wait to dive into their mysterious world. Equipped with detector, binoculars and camera I set off into the fading light to begin the search!
When I arrived at the visitor centre, I witnessed the sunset to end all sunsets. The glowing orb hung just above the birches, firing glowing orange wings out to its sides. Pink-footed geese flew in their huge skeins across the raging torrent of fantastical sparks. The reeds too kept the spirit of dusk; each moulting sheaf of seed swept in the steady breeze looked for all the world like a shifting, jumping flame. All this beauty shone once again in the rippling waters below, in equal vigour and saturation. In short, it was an outstanding view. Soon our tour leader, Lindsay Bilson, materialised from the growing darkness and introduced herself to our group. The event began with a quick intro into how to watch bats, and she spouted out an amazing wealth of knowledge on the subject. She informed us about her surveys of a rarity called Nathusius' Pipistrelle, and the final Greater Mouse-eared Bat wintering in Sussex. I thought I knew quite a bit about bats, and I was learning new facts constantly! As Lindsay explained all of the wonderful qualities these mammals have, we were all absolutely in awe of them and were very eager to begin searching. After a very informative talk about Britain's different species, everyone was handed a bat detector. I absolutely love bat detectors. The science of them astounds me; a machine that detects the echolocations of an animal making sounds that human ears are too primitive to hear, then converting the wavelengths into a frequency anyone can. You can control them by tuning the dial on the front to a specific wavelength, and checking which bats call on that wavelength. For example, the Leisler's Bat calls at around 20 kHz, whereas a Lesser Horseshoe-bat calls at 108. If you're detecting clicking or rattling on 20kHz, it will not be a Lesser Horseshoe, but could be a Leisler's. However do not be fooled. Often more than one bat calls on a single frequency; in which case the type of noise you can hear is helpful. We all tuned our detectors in to our first target, which we were all earnestly waiting for. 19 centimetre's wide, and fairly common in rural woodlands such as these. According to our knowledgeable leader, the roost here, in the RSPB workshop, had once numbered 500 or so, and that it had crashed in size to the mere handful present today. Soprano pipistrelles can be easily told from other small bats by their fittingly high-pitched calls, peaking at around 55 kHz. All we had to do now was to be patient.
However I was hoping that I would encounter an even bigger prize: the noctule. This is Britain's largest bat species, which emerges at sunset and tends to hunt while its still light. With a clear view to the west I could see a large portion of the sky, and I was hopeful that one may appear. They usually fly extremely high up over woodland edges, so I was in the perfect situation. And sure enough I soon glimpsed a dark shape hawking over the setting sun. It powerfully winged its way through the fading orange light, every flap propelling it higher over the canopy. Its silhouette was angular and bird-like, with very long wings, but sharply angular and jointed. I had last seen one of these incredible bats at RSPB Snettisham 3 years earlier and since had hankered after a good view like this.
When insects appeared the noctule swooped into their number, deftly changing direction at every branch or leaf. I hissed "There's a noctule over there!" at the rest of the group. They soon all turned their heads away from the outbuilding to watch this agile marvel of dusk as it plunged through the skies. Our first bat was one not to be forgotten!
After another few minutes, although half the group were still entertained by the noctule's antics, a steady trickle of sopranos was flowing from a crack in the brickwork. Their movement was hurried and confusing, seeming to whizz around in tight circles, and reminded me of rogue spinning tops! With the use of a bat detector the sound was very distinctive; a fast series of clacking notes, accelerating to irritable chirrups. As we made our way south toward the river this endearing noise faded into the creeping darkness. But because the darkness was setting in, a whole new array of sights and sounds introduced themselves. The characteristic twit-twoo of courting tawny owls rang through the woods to the left. Daubenton's bats began to commute across the path, flying out to the nearby pools to hunt insects. Daubenton's are almost entirely tied to open freshwater, so the River Yare and Reception Broad is the perfect spot for them to pick up all the midges they need! This was another new bat species for me.
Even as we trekked further into the woodland the high twitters of soprano pipistrelles followed us, still spinning amongst the upper needle-like branches of the birches. Yet I felt we would see something else noteworthy; that glimmer of hope inside a naturalist is rarely wrong. It wasn't. Because about 10 minutes later we heard a bat making slower graduated, regular clicks at 48kHz, and the realisation dawned. We spotted the Nathusius' Pipistrelle flying along the low hedge lines in an unwavering, straight path. It materialised for but a few seconds, showing a compact, angular form, then immediately its dark silhouette dissipated into the trees behind us. I was flabbergasted. I had hardly expected this rare a bat on a casual survey in South Norfolk!
For the remainder of the walk the darkness had advanced farther still, meaning we could barely see past our feet. Bats were still active but the temperature had now stooped to 9°C and numbers were thinning. Occasionally a Daubenton's or Soprano would linger for a few seconds, but it was clear the bulk of the horde had passed. For a while we waited beside the river to catch hunting Daubenton's bats, but no such luck emerged. Just ghostly, towering columns of mist rising from the still waters. We soon began our walk back to the visitor centre, very happy with the fruits of our walk. We'd seen spinning sopranos, swooping noctules and a wonderful rare gem: the Nathusius' pipistrelle. I'd had an excellent evening and learnt a great deal of useful info about these record-breaking critters, and I went out home that night with a renewed appreciation for them. In short, bats are incredible!
Daubenton Bat, Photo Credit: Bev Mulcrone
Blog written by Oscar Lawrence