Maternity Box Mystery Solved!

A blog post by our Training Officer, Chris Sherlock, about the adventures of a maternity roost in the south of Birmingham.  Their maternity roost has seen some increased activity, and Chris decided to investigate:


“The maternity bat roost box on the end of the byre has been there since 2008 and until 2012 we had seen no bats coming out. The box is on a building owned by a member of the bat group, and is where we hold some training sessions. Now there have been lots of bats and we know what they are!


The box was handmade and was put up as part of a European Protected Species (EPS) enhanced mitigation during the conversion of the byre to human living accommodation.  This was done under a Natural England Licence.  We often saw bats flying in the courtyard near the site of the box and there are bats using other mitigation that was put in, but nothing was in the large and cosy box, which was put up facing south west, near water and in an area of tree cover and mixed farm and woodland, including pasture which is regularly grazed. Surely no bat could turn it down as a home?


In August 2012 finally there were some bats emerging. At the end of the breeding season some bats were using the box. It might have been to do with change of use in a building near by that perhaps forced them to move.

Up to 20 bats came out of the box over some weeks in the later summer and early autumn. We were not sure what they were. Ashamed, we stood there with detectors and resolutely tuned up and down between 60 KHz and 40 KHz, trying to divide between the 2 possible sorts of pipistrelle. But all we got was bats sounding like pips but using 50 kHz.

So we could not agree if they were Pipistrellus pipistrellus using around 45 kHz (Common Pipistrelle) or Pipistrellus pygmaeus using around 55 KHz (Soprano Pipistrelle).  These 2 cryptic species were only divided in the late 1990s by genetic work at BristolUniversity.  The Soprano likes to live in larger groups and favours feeding over water and the Common is more of a woodland edge specialist and tends to roost in smaller groups.  We had a small group right by the canal, so that did not help!

In fact they are not as cryptic as first ideas suggested as the faces are different and the calls are often quite easily divided by the tune up and down method with a heterodyne detector when the bats are feeding and you have plenty of calls. But these bats were emerging in to quite a cluttered environment and rushing off to feed giving us no time on the detector to decide. The clutter often makes pips harder to divide as they use a call pattern that helps them navigate best.


The end of summer 2013 brought the bats back and in much greater numbers pushing in to the 80s and lots of droppings on the new wood store roof below

We did not want to hand net the bats and make identification that way and then they were gone for 2012.  But after a trip to National Bat Conference at Warwick in September 2013 and a conversation with Steve Parker from the Lancashire bat group about how to decide about “those pesky 50khz pips” which turn up all over England at least lead to the chance to have DNA analysis of the droppings!

Now we had lots of bat poo and a tiny little test tube and an address of a man at WarwickUniversity who would do the analysis!  Six fresh droppings should do it, so after being thwarted by heavy rain for a few days we collected them and arranged to send them off and pay.  Now the results are back from Dr. Robin Allaby the EcoWarwicker at Ecological Forensics at WarwickUniversity and we have had Common Pipistrelles in the box this autumn!


We are really pleased to be sure what the bats are and that the numbers seem to be increasing. We hope they choose to actually breed there next year. We will be out there with the detectors again and add recording and sound analysis to show that they are perhaps using peak energy at 50 kHz in this emergence setting. “