Leisler’s Bat Nyctalus leisleri is a large golden-furred bat with black skin. This species is also known as the Hairy-armed Bat as the underside of the wing membranes are furred along the body and up along the arms to the fifth finger (Zera, 2004). It is also known as the Lesser Noctule, a particularly appropriate name as it looks like a Noctule Nyctalus noctula but is noticeably smaller. Closer examination shows that the fur is longer, particularly on the back and over the shoulders, giving it what has been described as a “lions mane”. The individual hairs of Leisler’s Bat have a dark base, whereas Noctule hairs are uniformly pale brown (Zera, 2004). Leisler’s Bats are long winged and adapted for fast, sustained flight, They are known to migrate over distances of hundreds of kilometres, at least in the eastern part of their range (Hutterer et al, 2005).
Leisler’s Bats are widely distributed over the southern half of Europe but are not common anywhere other than Ireland. Within the UK they are concentrated in southern England with few records from the South West, the North East, East Anglia, Scotland and Wales (Richardson, 2000). The nearest known breeding colonies to the North East are around Wakefield.
Several national distribution maps show Leisler’s Bat as present in the North East (for example Harris and Yalden, (2008) and Russ, (2012), but there are only two unequivocal records. The first is the specimen found at Cragside early in 1986. The bat was originally identified by John Steele; Noel Jackson, Terry Coult, Rob Strachan and Gill Hinchliffe all crammed into a Mini for a hair-raising drive through deep snow to see the specimen. However while the bat’s identity is certain its provenance leaves some room for doubt as it was found in a wardrobe that had been brought up from southern England. The second record is from February 2012 when Tina Wiffen and Helen MacDonald identified a Leisler’s Bat which had been found in a bath in Wallsend near to the Rising Sun Country Park. This bat was successfully rehabilitated and released where it was found.
There have also been a small number of bat-detector records of varying levels of confidence, mainly in Northumberland. There are recordings from the Rising Sun Country Park in 2011 that were indicative of Leisler’s Bat, as was a recording of a single bat commuting up the river at Wallsend in June 2003. Claire Snowball’s May 2009 recordings from Havannah Nature Reserve near Newcastle Airport also fit the very probable category with John Drewett’s observations at Piercebridge at least a good possibility based on his experience of bat work. Analysis of data from the Bats and Roadside Mammals Survey 2006 (Russ et al, 2006) undertaken by Durham Bat Group in 2006 suggested Leisler’s Bats around Darlington and near Hamsterley Forest but follow-up visits failed to detect them in both cases. Similarly there have been a number of records based on the occasional bat pass recorded on a remote detector but many of these are at best questionable. To put this into context, no member of Durham Bat Group considers that they had even “probably” encountered Leisler’s Bat in County Durham or Cleveland.
In conclusion, there is so far no record of a breeding population or even anywhere where Leisler’s Bats are regularly present. On the basis of proven or very likely records, we could conclude that Leisler’s Bat is just a slightly more regular visitor to the North East than other vagrant species. However, we know that several insect species have colonised the North East in recent years and it may only be a matter of time before Leisler’s Bat breeds in the region as well. Indeed an alternative explanation for the records is that we may be on the cusp of that colonisation process.
Written by Noel Jackson (last updated Nov 12)