Friday, 15 June 2012

The art of radio-tagging a bat

People sometimes ask me when I'm going to write my next blog post. The honest answer is that I'd love to write posts more often, but much of my time is taken up by doing bats surveys, writing reports, analysing bat calls and all the other myriad tasks that keep me busy whenever bats are active!

Here, to keep you going, is an example of what's keeping me from blogging. It's a great set of photos taken by Mike Beard, showing my colleague Rebecca Brassey and I (with help from Isla, Richard and Mike) preparing some Noctule bats for a radio tracking project this spring.

First find your bat. Here it's Rebecca's turn to check a bat box and see if our target Noctules are there. Typically, we found a group of them in the very last box we looked in.


Before attaching the radio tag, biometric data was gathered about each bat. First the bat is sexed, the forearm is measured with a pair of callipers and then the bat is weighed.


Weight is especially important as I need to be sure that the radio tag will weigh less than 5% of the animal's body mass. The ratio between forearm length (which doesn't vary once a bat is adult) and weight is also a useful indicator that the bat is healthy and therefore a suitable candidate for radio-tracking.


Next I wanted to age each bat. This is hard to do with non-juveniles, but with larger bat species it is sometimes possible to get a hint of age by looking at wear on the teeth.


Another feature which can help with understanding the age of a bat is the amount of scarring on its wing membranes, though again this is an imprecise science!


I hadn't examined this colony for ectoparasites previously, so each bat was examined and with Rebecca's help some specimens of Spinturnix acuminatus were taken. This is a species of wing-dwelling mite normally found on Noctules.



The specimens are preserved in a 70% solution of Isopropyl alcohol and labelled in pencil on small slips of paper, which are inserted in the vial with the specimen. This prevents the specimen and label from becoming separated.


Next I check the manufacturer's label on the tag, so that we can check the radio frequency of it's "chirp" transmissions. I am also double-checking the weight of it, to ensure it is below 5% of the bat's weight.


A small patch of fur between the bats shoulder-blades is snipped short. This location is used for the tag, as it is a hard location for a bat to reach to groom the tag off. That won't stop it's roost-mates from having a go.


A thin layer of mastic glue is applied to the trimmed patch of fur and allowed to cure until it is sticky.


A similarly thin layer is applied to the tag....


...and the tag is pushed firmly in place.



Next another layer of glue is painted over the top of the tag...


...and the adjoining fur pulled over it.


In this picture you can see the tag's antenna, the thickness of a human hair, trailing behind it.


Voila, one Noctule bat, with radio tag attached and ready to be released at sunset.



The tags of course do not harm the bat: after a short period the fur will grow and either the tag will fall off naturally or it will be groomed off. But for a few days or weeks the bat will give us a windows into it's life:when and where it hunts, where it roosts, whether it associates with other bats and so on.


My thanks to Rebecca, Isla and the various trainees and volunteers who helped out with this particular project and of course to Mike for the photography.

Please note: all bats are protected from disturbance and harm in the UK and EU. This type of work should only be undertaken by experienced personnel under a specific license, issued by the relevant statutory nature conservation organisation (Scottish Natural heritage, Natural England etc). Attempting to handle bats without an appropriate license is a criminal offence and carries risks. If you are interested in getting involved in working with bats on a voluntary basis contact your local bat group (The Bat Conservation Trust will put you in touch with them). 

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