We were at a campsite in Brittany this summer, in a green valley thick with oak woods. On our second night there was an announcement on the chalkboard outside the reception hut:
22h BATS + HOT CHOC
BRING TORCH AND MUG
Who could resist?
10pm that night we turned up at the hut, and followed a trail of waggling torch beams around to the river side of the the old mill building. The group of 15 or so people, parents and kids, gathered to listen to the campsite owner, himself a dad with young kids.
The mill was a hundred and fifty years old, and disused for half a century. A big, broken, rusty old mill wheel, like something off a paddle steamer, leaned against the rough stone wall. We could make out the black rectangles of window openings along the upper story, where the bats live. 500 of them. The second largest colony of their species in France. By this hour most of them had come out to feed, and by torchlight we could pick out two or three zipping back and forth across the surface of the dark water.
Our host directed a handheld monitor towards them and it crackled like a Geiger counter, translating inaudible squeaks into something we could process. We learned that while human hearing goes up to about 30kHz and dogs to 60kHz, these little critters operate at 120kHz.
They fly blind but see by echolocation, snapping up a midge every couple of seconds. In two or three hours of the night they’ll consume twice their own weight in midge. I guess that means coming home weighing three times what you did when you kissed the family goodbye and flew off to work.
If you’ve ever been in the Scottish highlands or similar latitudes on a summer evening and tried to swat a midge, you’ll know it can’t be done. They’re fast, and practically too tiny to see. To them, we must be as big as the Eiffel Tower, and almost as immobile. But the bats have got midges figured.
Clever little things! There are over a thousand species of bat in this world, filling niches across the land. Much reduced in total number these days as their habitats have been occupied or eliminated, but this wooded valley, with its appealing old mill building and unpolluted, midge-rich river, is a still a niche that needs them.
Another canny feature of their lives that our host told us about: in autumn the bats congregate at a wooded spot downstream to meet and mingle with other colonies. They mate, but the females don’t fertilize until spring, once they’re sure it’s going to be a good season for foraging. They raise a single baby bat every one or two years.
The hot chocolate was ladled from a big shiny vat, and was as good as any I’ve ever tasted.