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Wednesday, 21 May 2008

A Bat in the Hand....

...takes a great deal of work to achieve!

In company with a small group of people from Lothians and Scottish Borders bat groups I attempted to try out my new harp trap last night (see "The Kitchen Table Harp Trap", under February 2008).

The site was a ruined castle, set in a secluded valley in the Scottish Borders. "Ruin" is probably the wrong word, as the seventeenth century noble who set about building it never completed the job but, with massive stone walls up to 50 feet high, it really looks the part. Barrel-vaulted cellars with plenty of deep gaps and cracks in the stonework provide good roosting opportunities for bats. There are woods and a river close at hand, providing foraging opportunities for several bat speices and in the past we have trapped Natterer's Bats (Plecotus nattereri), Daubenton's (Myotis daubentonii) and Brown Long-eareds (Plecotus auritus).

Trapping bats is enjoyable, but there needs to be a valid scientific reason to interrupt the bats in their normal activity. On this occasion bats were to be rung as part of a long-running study of bats using sites of this type in the Scottish Borders. In addition, I was planning to remove parasite specimens as part of my studies into their distribution and host associations.

Two harp traps were put in place: mine and a slightly larger one, each covering the entrance to one of the cellars. There is an art to siting a harp trap: it needs to cover as much of the entrance as possible and gaps need to be filled as far as possible, to prevent bats flying round the trap. A tarpaulin, some leafy twigs and an old coat were pressed into service around my trap:

It was quite cold, dipping as low as 5 degrees centigrade after sunset and bat activity wasn't high, apart from the large numbers of Soprano Pipistrelles (Pipistrellus pygmaeus) dispersing from their roost in a nearby farmhouse. Nonetheless, we caught four male Daubenton's, all of which emerged from one of the cellars. Frustratingly, it wasn't the cellar which had my trap at the entrance!

Two of the bats were recaptures and had been rung on previous visits to the site, but the other two were new and, as well as being weighed and having their forearm length measured, each had a tiny numbered aluminium ring slid onto it's forearm.

None of the bats had many parasites. This is often the case in spring, especially with adult males, which usually carry a lower parasite burden than females and juveniles. They are able to move between roosts to avoid parasite accumulation, whereas the females and juveniles are together in the maternity roost for several weeks each year, often with many other bats. I like to think that juvenile bats may also have similar personal hygiene issues to many human teenagers!

The picture above shows the fouth bat to be caught, who caught my interest as he had a tromiculid mite larva in his ear. The Trombiculidae are a large family of mites, including members of the genus Leptotrombidia, which parasitise bats for part of their life-cycle. Their larvae hatch within a bat roost, climb onto a bat and attach themselves, often in the bat's ear or on the forearm. There they take a meal, before dropping off the bat to become predators of other small arthropods within the roost during their nymph and adult phases.

I was particularly interested, as there are very few records of these parasites on British bats, partly because records of any bat parasites are rare and partially because they can be difficult to remove. Fortunately, this bat was quite placid and, with Carol-Ann (the "bat whisperer") holding him, I was able to paint the mite with a little isopropyl alcohol using a very fine brush, to make it release it's grip, and then remove it with fine soft forceps.

Once home I checked and have been unable to find any records of a trombiculid mite on a Daubenton's bat in the UK (unless anyone reading this knows better?), although that doesn't necessarily make it a rare species: probably just an under-recorded one. It will probably be a while before I am able to positively identify it to species: there are no field guides!

I haven't mounted the mite yet, but here's a rough and ready picture taken at x120. The larvae are usually a distinctive orange colour when seen on a bat. With their mouthparts buried in the bat, they look like tiny orange jelly beans.

As for the harp trap, it is still waiting to be christened with it's first bat. Watch this space...

Please note, trapping and handling bats without proper equipment, training and experience can be very harmful. Furthermore, in the UK it is illegal to do so without appropriate licences from Scottish Natural Heritage, Natural England, the Countryside Council for Wales or the Environment and Hritage Service in Northern Ireland.

If you're interested in getting involved in working with bats, the best starting point is your local bat group:

A checklist of mites found on British bats can be downloaded here:

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