|Bat team, winter 2015-2016|
|The Batacombs: spot the bat ... (c) Greg Slack|
Fitting with the dripping, cave-like ambience, our torch beams pick out overwintering peacock butterflies, convincingly camouflaged as dead leaves, herald moths, snails bleached to a limestone white, and massed clusters of flared-skirted southern pill woodlouse. One fissure in a wall contained a huddle of Eristalis drone flies. Cave spiders guard their ping-pong egg sacs high in the corners. Among the darting flattened-plane, two dimensional shadows thrown about by the torch sweeps, suddenly there is a small, darker, more solid shape.
Just as they are meant to, the horseshoe bats hang upside down from walls and ceilings, though it is still somehow eerie to see them suspended impassively there, like strange dormant leathery fruits, or tiny thumb-sized folded-up umbrellas (our other UK, non-horseshoe, vesper bats do not generally do this, but tuck themselves tightly into nooks and crevices). This year curiously the horseshoes have been clinging to the open walls quite low down - something to do with unseasonal temperatures this winter? At the alcove, one almost had to climb in to the stone coffin to see an individual bat clinging to the underside of the lid.
|Strange umbrella fruit: lesser horseshoe bat (c) G. Slack|
|Cave spider, probably Meta menardi, guarding egg sac|
|Habitat enhancement, Narnia style|
Over the last 18 months we've recorded bat droppings in the wardrobe, but no roosting or hibernating bats so far. This winter our hibernation counts were 8 lesser horseshoe bats in January (temperature 2-3 degrees C) and 4 lesser horseshoes in February (temp. 9-10 degrees C); also a single Natterer's bat, with its snowy white tummy fur. Our monitoring results will contribute to national bat recording schemes. These numbers sound low, but, perhaps surprisingly, this is the 9th highest known winter roost for lesser horseshoe bats in Devon; this, in a part of the country which is a stronghold for both greater and lesser horseshoes.
And how common is this phenomenon of urban horseshoe bats, let alone urban overwintering bats, when built-up areas would be expected to be unsuitably warmer than surrounding countryside? (See Tania Esteban's blog for a discussion of urban bat ecology). There seem to be few examples from the UK: the only urban horseshoe bats we've come across up to now are here in Exeter, and in Taunton; any other records would be of great interest.
If you want to find out more about Exeter's bats, please join us for our annual Pips & Pints event this May, a joint event run by DWT Exeter Local Group, Exeter City & East Devon Bats, and Devon Mammal Group.
Exeter LG (link to event details will be here in due course)
Exeter City & East Devon Bats
Devon Mammal Group