Species of the day: Pipistrelle Bats

By James Duncan

Learning and Engagement Officer

The Pipistrelle bats are Britain's most widely distributed and regularly seen species. Confusingly, the Pipistrelle isn't a single species of bat at all, it is in fact three, comprising the Common (Pipistrellus pipistrellus), Soprano (Pipistrellus pygmaeus) and rarer Nathusius' (Pipistrellus nathusii). Even though subtle differences had been previously documented, quite amazingly it wasn't until the 1990's that re-classification commenced and the species were finally separated. The Common and Soprano are however, the two you're most likely to spot. Incredible to think, that for centuries these common denizens of the dark went about their business without anybody realising they were really quite distinct. Of course, it's the very habits of bats that make them difficult to observe in the first place. They exist on the limits of our sensory perception, usually observed as a flicker of wings before once again disappearing into the darkness. Fortunately, the Pipistrelles' wide range of habitat preferences include our very own urban surroundings. They typically emerge just after sunset, so should you happen to look up after dusk you may well spot one as it manically whizzes around after its insect prey.

Bats belong to the substantial Order of Chiroptera translating from Greek as 'hand-wing.' Somewhat amusingly the German name for a bat is 'Fledermäuse', not unsurprisingly translating to 'flying mouse.' Though they certainly have the appearance of flying rodents, they're very much more closely related to us humans than rodents. The anatomy of the bat is indeed remarkably similar to our own and is typified in the bat's wing. Though the relative bone lengths are substantially different, the bats have in essence a human hand and arm with the equivalent bones. They're contained within a thin membrane of cartilage known as a patagium, which enables them to 'swim' through the air, giving them unrivalled agility and maneuverability. They are simply superb flyers, an essential considering their need to gorge on a few thousand insects every night. The huge appetite for such a tiny mammal consists largely of flies (particularly midges, mosquitoes and gnats), caddisflies, lacewings and micro-moths. The Pipistrelle's exemplify aerial hawking, where prey is pursued, captured and consumed in flight. 

Common Pipistrelle © Hugh Clark FRPS 

The two most numerous Pipistrelle species really are 'edge' specialists and it's along tree-lines and tall hedgerows where you're most likely to spot their highly distinctive 'jerky' and erratic flight. The Soprano Pipistrelle tends to favour wetland habitats, but both usually hunt up to around ten metres from the ground. When observed on a warm evening they will undoubtedly appear significantly larger than they actually are. They are in fact our very tiniest bat species, but it's their wingspan that's deceiving. Whilst this may reach around 24cm, the body is minute, only around 4.5cm, which is roughly the same as a matchbox. Even the very largest of the Common and Soprano's won't weigh more than a 50 pence piece. Owing to this diminutive size, they belong to a family of microbats, known as the Vespertilionidae. Like all British bat species, they're entirely insectivorous, separating them from the larger fruit-eating megabats. The bats are truly globe-spanning and comprise around a fifth of all mammal species on Earth and around a quarter of all resident mammals in Britain.    

Though the Pipistrelle's may roost in tree holes, crevices and bat-boxes, buildings are a particularly favourite. Any suitable crevice may suffice, though cavity walls and gaps behind tiles, soffit, eaves and boarding often fit the bill perfectly, providing habitat for both summer maternity roosts and winter hibernation roosts. Upon emerging, trees and woodland will prove essential features for their navigation, leading them to preferred foraging areas where feeding can commence. Like many bats, the Pipistrelle's have reasonable eyesight, though it is of course echolocation that enables them to hunt so effectively. Sound waves are emitted from the mouth, the bat version of 'shouting', and it's only when these waves make contact with an object (or prey) that they return as echoes. The bats carefully read the rapidly-returning echoes in order to build an 'aural image' of both their surroundings and the pursued prey. The precision enabled by echolocation enables the bat to ascertain the size, shape, position and movement of an object with pinpoint precision. Amongst Pipistrelle's, the peak frequency of the echolocating call is the very feature used to separate the three species. Though a bat detector will be required, a peak of 45kHz helps to determine a Common Pipistrelle, whereas 55kHz will denote a Soprano Pipistrelle.