Wednesday 4 September 2013

A very unexpected bat...

'On the very last day, at the final hour, just as they were packing up...' Funny how often it seems to go that way with natural history, a lesson on never giving up too soon!

Martyn Cooke and helpers, setting up a bat mist net on the edge of Brockley Wood

On the evening of Monday August 19th, a small group of us set off to the woods on a rather different kind of wildlife survey. Martyn Cooke of Surrey Bat Group is a licenced bat trapper and handler, currently working on a large project spanning the borders of Sussex and Surrey. Much is still unknown about bats in the UK such as their current numbers and their social and mating habits. I imagine that even less is known about bats living near an airfield! 

North West Zone with Brockley Wood, River Mole and grasslands

We set up two large mist nets and a harp trap at Brockley Wood with high hopes of capturing something. As the sun was setting we could even see bats flitting along Man's Brook. Our two mobile bat detectors were quickly switched on and we began picking up calls of both Soprano and Common Pipistrelles along the treeline.

Setting up the Harp Trap and an electronic lure

Bats are highly protected under both European and UK legislation and all trapping work is strictly licenced. The harp trap and lure was devised by Sussex University; basically a metal frame with vertical fishing lines strung-up between and a canvas collecting bag at the base. The lure is an ultrasonic loudspeaker which plays pre-recorded bat calls - not the usual calls made when bats are hunting or navigating, instead the social calls made when they are communicating with each other. This draws in curious bats which cannot detect the fine wires of the trap, so they bump into it and then slip unharmed into the bag below. 

Scrubland West of Brockley Wood. A great place for moth-chasing while the sun goes down.
(Photo by Joe Bicker)

After some time spent setting up the traps, then came the waiting game. We wandered about between the two nets, looking out for signs of anything caught up in it. Although we were detecting some bat activity nearby, tonight these nets remained determinedly empty.

Common Blue butterfly roosting in the dark (Photo by Joe Bicker)

We finally began packing up sometime before midnight, making the decision to take down the mist nets first and leaving the harp trap until the last possible moment. It was with baited breath that we approached the harp trap for the final time, trying not to get our hopes up....

Scored! 1 mystery bat (Photo by Joe Bicker)

....we struck bat! Such a great reward at the end of a long evening. It was difficult to tell which species this was right away. Martyn took a closer look and was pretty lost for words; this little lady turned out to be a Bechstein’s bat (Myotis bechsteinii), one of the UK's rarest bats! 

An exciting find: a rare female Bechstein's bat (Myotis bechsteinii) 

A Bechstein's in the hand is worth a thousand in the belfry... (Photo by Joe Bicker)

The southern counties of England from Dorset to Sussex are where Bechstein's bats are most likely to be found in the UK. This young female was actually within range of a known Bechstein's colony, but it was still a pretty unexpected find in a fragment of woodland next to an airfield!

Impressive ears match the impressive gape - important features for a night-time aerial hunter of insects (Photo by Joe Bicker)

Assistants Emma, Joe and James watch while Martyn takes the biometric data. 

Martyn is a trained expert in bat trapping and handling; first he determines the sex and general health, then takes various measurements such as weight and forearm length. He was able to determine she was born sometime in June and although slightly small for her age, her weight was within the healthy range. Afterwards the bat was released unharmed and we felt privileged to have been in her presence!

Moment of freedom: We didn't take up too much of her time and she flew quickly away from us

Our little Bechstein's call sequence, displayed visually here as a sonogram. 

As she flew out of Martyn's hand I made a recording of her ultrasonic echolocation calls. Taking these recordings and analysing them through smart computer software means we can get better at identifying individual bat species without capturing them. There is a chance we could have a small colony of Bechstein's using Brockley Wood and the mature trees along the River Mole corridor. Martyn will be continuing his work through trapping and setting up his passive bat-detectors around Gatwick's woodlands.

Soprano Pipistrelles in their mating roost

We also have several bat roosting boxes up around this and other woodlands which we will check and clean out each year. Here is a bunch of lovely little Soprano Pipistrelles (Pipistrellus pygmaeus) Martyn and I found last week, all huddled up in a sleepy bundle.

For more information about bats and the UK's bat species visit the Bat Conservation Trust website

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