I Like Big Bats (& I cannot lie)

So I’ve had a bit of a hiatus from blogging and social media, due to personal reasons, but I have lots to share with you and catch up on – not least, the significant finds as part of the BrumBats Batlas project and our bat box scheme. I’m going to blog this weekend about our second (and most exciting) discovery, but for now I want to talk about big bats.

There are three closely-related species of bat which are generally lumped together as being our ‘big bats’ in the UK: serotine (which I’ll focus on another time), noctule and Leisler’s bat. The latter two species are pictured below, and are superficially similar. They are both quite chunky bats, with the tragus (the flap of skin inside the ear) shaped like a mushroom, but the noctule is larger (weighing in at up to 40g – twice the weight of a Leisler’s) with paler (often gingery) fur compared to the dark brown fur of Leisler’s bats. Leisler’s also have a thick ‘mane’ of ruffled fur around their shoulders and head.

Noctule
Noctule
Leisler's
Leisler’s

Noctules (Download the BCT factsheet here) are one of our largest UK bats, and are fairly ubiquitous, found throughout Birmingham and the Black Country, whereas Leisler’s bats (aka ‘lesser noctule’ – fact sheet here) were until recently only know at a couple of sites. The 2002 mammal atlas (Which you can download here) shows their distribution as follows:

As you can see, Leisler’s bats are fairly scarce. Or are they?

You see, in the 13 years since the atlas was produced, BrumBats have been actively recording bats across the county, and (especially since the 2014 launch of our Batlas Project) we have recorded noctule in pretty much every tetrad we’ve surveyed.

(BTW, the maps don’t look like this anymore. The thing is with distribution maps is that they are a map of the RECORDS of a species, not of the species itself, and often are a reflection of recorder effort. If a person is really into recording bats, they are likely to have concentrated their efforts in ‘likely’ or ‘favourite’ spots. This is where systematic surveys like the Batlas come in – they dilute the skew on the data provided by biased recorder effort.)

So noctules are apparently all over the county, but Leisler’s bats are a different matter. In 2015 we had a Leisler’s bat come into care from Wightwick Manor National Trust. The bat (which subsequently died of his injuries) was found at the bottom of their chimney. The Batlas Tetrad survey of that area the following year recorded Leisler’s bats foraging over a nearby woodland. So they are definitely in at least the outskirts of Wolverhampton.

Then, last year the awesome folks from the Herefordshire Mammal Group led several nights of mist netting and harp trapping for us. On one of these nights we caught a Leisler’s in a harp trap at a previously un-studied LNR in Walsall – not far from the town centre!

Then earlier this year, our successful bat box scheme at Merrions Wood turned up both Noctule AND Leisler’s using the boxes for the first time! So now we know some actual roosting sites, rather than just errant records of noctules flying over our area off to who knows where looking for food. This is all good stuff!

So I’m pretty excited about this, as we are getting an idea that although perhaps not abundant, Leisler’s are probably at least widely distributed across the county, just like noctules. But this then begs the question – how many of our noctule records are actually Leisler’s bats?

It is easy to fall into the trap of assuming that because we are in an urban area, we’re only going to have crap (sorry, common) species. I see this type of assumption made all the time over a variety of taxonomic groups. In the case of noctule and Leisler’s, both species echolocate at a peak of around 25kHz, with relatively similar calls (listen to Noctule and Leisler’s here) – pretty similar, right? You can separate them on sonograms, but not reliably just by ear.

lelislers
Sonogram of Wightwick Manor Leisler’s bat calls

I believe that Leisler’s bats are probably drastically under-recorded in our county. They are an adaptable species that we know can thrive in urban habitats (they are ubiquitous in urban parts of Northern Ireland, where noctules are not present at all).

So I’m hoping to focus future survey efforts on rarer (or under-recorded) species in the 2017 season, and I simply cannot wait! Stay tuned for even bigger news next week…

3 Replies to “I Like Big Bats (& I cannot lie)”

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