Nature Notes

Hawking Bats.

Late one evening, just after sunset, I thought I’d startled a woodcock into flight ahead of me; this most crepuscular of birds glanced low out of the edge of the wood and flew away down the ride with its characteristic twisting, bat-like flight. But I wasn’t sure, in the half-light; it was half the size, less ‘solid’, too bat-like. It fluttered slowly on ahead, and was about to round the corner of the wood, where I knew I might lose it in the parkland, but as it turned, it swept briefly into a patch of light, and I glimpsed the flicker of the web-winged silhouette and ears of a brown long-eared bat.

I would have been pleased with a woodcock sighting, but a long-eared bat was a rarer treat. This largely deciduous wood and open parkland, untreated with pesticides and near old farm buildings makes for a good habitat.

As well as being able to hawk moths out of the air at speed and manoeuvre through dark woods, they are masters of slow flight, even hovering to find beetles, day-flying moths, earwigs and spiders on foliage, gleaning them off leaves and tree trunks, on the wing. They have been known to scoop moths away from lighted windows.

As well as using echolocation, long-eared bats use their large eyes and larger ears to pinpoint prey. With such highly sensitive, low frequency hearing, they can hear an aphid’s footsteps on a beech leaf. Their ears are astonishing, and ¾’s of the length of their body. At rest, the ears are sometimes tucked under their wings, or curved back on themselves like rams horns, around the central, triangular aerial of the ‘tragus’. When in flight, the thin ears are inflated and held erect with pulses of blood.

Although tiny enough to slip between roof tiles, the wingspan of delicate skin is around 25cms across; yet this is a bat agile enough to pluck bugs from thorn bushes without damaging itself. Bigger moths, such as large yellow underwings, are often caught on the wing, taken to a branch and eaten upside down, the detached wings twirling to the floor.

Buoyed by my sighting, I hurry over to the playing field pavilion before dark. Its silhouetted apex emanated 100’s of pipistrelle bats on summer evenings. But it’s a chilly night, and I count only a dozen. This year’s babies may have left for other roosts, whilst, faced with a winter of too few insects, a bat’s evolutionary choice is to migrate, starve or hibernate – all 17 of our species hibernate. Long-eared bats are tougher, waiting for a succession of frosts, but here it seems, most of the pipistrelle colony has already slipped into a torpor under the roof.

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