The light was just beginning to fade as we gathered for an Essex Wildlife Trust bat evening at the Langdon Hills nature reserve. In the visitors centre around fifteen interested souls were soon listening to the leaders briefing for the evening’s escapade.
After tea, coffee and biscuits (how civilised), we trooped out into the gathering gloom armed with torches and with bat detectors at the ready. Thankfully, after the wind and rain of recent days, the evening was dry, still and by comparison of late, mild, so the stage was set for a successful evening.
We had only walked about 100 yards and had just entered an area with trees either side of the path when the first urgent, rapid clicking on a number of detectors could be heard. We had found our first bat (or was that bats?) of the night! The group stopped and were pointing the detectors in all directions and you could hear a barrage of clicks from the line of detectors. At times it seemed the clicking would start at one end of our line and as the bat flew past the clicking would move to other detectors along our line. Although we could ‘hear’ the bats, seeing them was another thing and, with the trees around us, it was now quite dark but as our eyes become adjusted to the conditions we did manage glimpses of these fast, erratic, flying mammals.
Moving on to the lake, we positioned ourselves on the bank looking out across the still water and in the sky towards the west, the last ribbon of the fading daylight. You could hear the nocturnal honks and quacks of the geese and ducks and see their dark silhouettes gliding along on the far side of the water.
It was not long before the bats were running the gauntlet of our detectors, bringing them to life with hurried click- click-clicks, as they passed in their jerky flight. Once again, despite the numerous audio warnings of their approach, it was not easy to see them and we did wonder just how many bats were around. Some tried shining a torch across the water hoping to pick out a bat skimming the surface hunting for insects but this was largely unsuccessful. We had been there for around 45 minutes when slowly, perhaps coinciding with the dropping temperature, our detectors eventually fell silent.
As we made our way back, now using the torches to aid our progress, a few detectors clicked away as we walked between the trees where perhaps the shelter they provided meant that winged food could still be found. After the recent run of poor weather, I imagine that the bats would need to make the most of the kinder conditions and to continue to feed for as long as possible.
Bats hunt by using echo location - that is, they emit a high pitched call that bounces back off their prey. To distinguish between some species, it is necessary to know the frequency of their calls and to set your set detector to that frequency (e.g. the call of the lesser horseshoe bat is at 110 kHz). Most of the bats were identified as pipistrelles but we did think we saw one Daubenton’s bat over the lake, taking into consideration its flight pattern, size and its liking for hunting near water.
Before this evening, I was thinking of purchasing a bat detector and it was a good opportunity to talk to others with experience and see what types they were using. I was hoping that there was one that I had only to point at a bat and it would tell me which species it was. Guess what, it is not as simple as that! A fair bit of skill, knowledge and software is needed to pinpoint a species. So I think I will opt for a fairly simple model!
On my return home I was just locking the car when what did I see fly past a nearby streetlamp? Yep, a bat!