Whilst the noctule no longer holds the title for the UK’s largest bat, it still acts like it is. It lives in trees, where it is found year-round; unlike the other wimpy bats, which head underground when it gets too cold.
Anatomy
The noctule weighs in at a monstrous 18-40 grams, with a head-body length of up to 8cm. Noctule bats have broad, rounded ears which do not meet on the top of the head. Inside the ear is a kidney-shaped tragus – typical of species which fly in the open.
Their glossy, short, and sleek golden-brown fur perfectly matches the brown-rot caused by certain wood-decay fungi. Furthermore, their heavy brow and substantial nose give them a slightly grumpy appearance. When viewed from the front, they even resemble the original Series 3 BMW.
Learn how to identify the noctule bat by watching this video.
One of the noctule’s many interesting behaviours is ‘milk theft,’ where a youngster who has lost its mother tries to feed from another female. This sneaky tactic rarely works, but a few manage to get away with it.
Ecology
Feeding
Like all UK bats, noctules are insectivorous. Beetles, moths, butterflies, flies and caddisflies are the prey of choice.
With strong and fast flight, noctules often get mistaken for swifts, as they share a similar flying style. Typically, they forage above the treetops of broadleaved and mixed woodland, reaching speeds of up to 50km/h while diving in pursuit of prey. They catch insects mid-air using aerial hawking and eat them in-flight. Their core foraging zone extends up to 4km from their roost, but they can travel as far as 25km.
Like all UK bats they are nocturnal, hunting at night using echolocation. In the open, they use two distinct calls types: frequency-modulated/quasi-constant-frequency (FM/qCF) and quasi-constant-frequency (qCF) calls. They alternate between these two, producing a ‘chip-chop’ sound on bat detectors.
Interestingly, they can adjust their calls based on their surroundings, dropping FM/qCF calls in open areas and qCF calls in cluttered spaces.
Officially the UK’s toughest bat – the only bat who has fought a grey squirrel and won!
Reproduction
In late summer and early autumn, male noctules establish mating roosts. Their mission? Attract a harem of up to five females. Their method? Shout as loudly as possible from the entrance of the roost and produce a powerful odour. Females choose their mates based on the display and the quality of hibernation sites, where they spend the winter with the males.
In spring, the females disperse in search of food. By June, they gather to form maternity roosts, typically containing 20 to 60 individuals. Each female gives birth to a single pup in late June or early July, though twins have been recorded (albeit rarely). Pups rely entirely on their mother’s milk for up to four weeks before weaning. After two more weeks, they must forage for themselves.
Habitat and roosts
Noctules almost exclusively roost in trees and have a particular fondness for woodpecker holes. Alongside these void-features, they also use crevice-features like hazard-beam cracks. On rare occasions, they hibernate in rock fissures or gather in buildings for social occasions.
In Germany, some noctules hibernate in bridges, with up to 5,000 recorded at a single site. Meanwhile, in the UK, their tree roosts can host up to 200 bats – cosy!
Their loud, social ‘chatter’ is easy to hear without a bat detector. On a summer evening, take a walk through your local woodland and listen for these vocal creatures.
Location and habitat
Noctules are one of the most widely distributed species in the UK, being found throughout most of England, Wales and as far north as south-west Scotland. They are absent from Northern Ireland and the Republic of Ireland, most likely due to the absence of woodpeckers – which create their preferred roosting cavities in trees. They are pretty hardcore, and have been found ‘chilling’ in their roosts at temperatures of -9 degrees Celsius. This tolerance for cool temperatures explains their presence in southern Sweden and Norway.
