Radio tracking the lesser horseshoe bat in Dromore, Co. Clare
A Cork County Bat Group member, Daniel Buckley, then a first year student at University College Cork, got the unique opportunity of taking part in a radio telemetry study of the lesser horseshoe bat in 2002. Here is his account of what tracking tagged bats is really like.
In summer 2002 I was given the opportunity to take part in a radio-tracking project on the lesser horseshoe bat Rhinolophus hipposideros. Sinead Biggane, a postgraduate of NUI Galway, was undertaking the project, which was based in Dromore Co. Clare. The roost is situated in an old stable adjacent to Dromore Nature Reserve and consists of between 370 and 400 females and juveniles making it probably the largest maternity colony for this species in the world. The current Irish population is quite healthy at between 10,000-12,000 individuals. The importance of this roost was recognised and in 1998 the property was purchased by the Heritage Council who carried out much needed repairs to the roof, secured the property by installing locks and boarded up windows and doors.
Sinead wanted to find out where the bats foraged in the surrounding countryside and most importantly what commuting routes they used so that when these were identified they could be protected. So, under government licence, the radio tracking would also give some insight into the behaviour of the bats and answer such questions as; when did they leave the roost, how long did they forage for each night and did different bats have preferred foraging areas? She especially wanted to know if the colony only foraged within the nature reserve or if they also foraged in the unprotected countryside. If they did she hoped that her work would help in the protection of important habitat. She also wanted to try and locate the colony’s hibernation site so it could be protected ensuring year round safety for the bats.
I started work as an assistant radio tracker in June. We started out by catching horseshoe bats using a mist-net placed outside the stable along one of the known flight paths that Sinead had discovered during her research. The capture of the bats was very weather dependent and we could not mist-net or tag if it was raining as the net and bats would get soaked. The bat that was to be tagged had to meet certain criteria so it was imperative that we caught at least a dozen bats to get two for tagging. The bats had to be a good size and weight to be able to carry the tag without being affected physically. Preferably the bat should be a female for consistency and because it was a maternity colony. When they were caught, the bats were weighed, sexed and forearm length was measured.
The chosen bats were ringed so they could be identified if recaptured or if found hibernating. The fur was cut between the shoulder blades and the tag was attached to the skin using skin bond adhesive that would eventually breakdown and allow the tag to be pulled off by the bat causing no harm to the animal. This glue would not work if the bat’s fur was wet. The tag would emit a signal at an identifiable frequency that was picked up by a receiver, which was carried around by the radio tracker. The strength of the signal would tell us the distance and direction of the bat so it could be followed throughout the night. A round of radio tracking would usually last as long as the battery in the tag lasted or until enough data was collected from the bat, usually 8 or 9 days. This was followed by 4-5 day gaps. Unfortunately we were unable to tag bats during most of July, as the bats were giving birth and raising young and tagging would add to the stress of this time of year.
When tracking a bat, one’s behaviour is altered to fit into that bat’s lifestyle. You start work when the bat leaves the roost, you follow the bat wherever and however long it forages and you only take a break when it takes a break and you can only return home to bed when it does so. For me it was a unique insight into bat behaviour. For the first time I was allowed to see what a bat did when it was out in the countryside instead of just hearing a sound from a bat detector. We spent a lot of time in the nature reserve, a beautiful place consisting of 400 acres of mixed deciduous woodland and lake. The world looked totally different at night and there was a lovely peaceful atmosphere on warm summer nights when walking amongst the trees. An added bonus of working at night was the encounters with other wild creatures. We always met the local badger clan and the cubs were especially cute. We also often saw foxes, owls and wood mice.
I had three very memorable wildlife encounters that summer. The first was with a pine marten, a beautiful shy creature. The second was an otter as it fished for eels from an eel trap in a nearby river. The third was when I photographed a pied flycatcher in an old hazel tree. This bird is a very rare summer visitor. I also regularly saw other species of bats; Daubenton’s in particular as they foraged over the lakes in the reserve.
The lesser horseshoe bats usually rested in a building, particularly Dromore Castle, or a tree between foraging and when they took a break so did we and let me tell you, after three hours of walking after a bat, chocolate bars and coffee in the front of the car was absolute heaven! Of course radio tracking isn’t all fun and games especially during bad weather or if you are walking through dense hazel scrub and holding an aerial up at the same time in the dark or if your bat decides to take you on a merry romp through a quagmire! But, all in all, I found it was an amazing experience and I felt privileged to be involved in the project especially one that has some real benefits to bat conservation. It certainly was the best summer job I ever took and would recommend this type of fieldwork to anyone who is interested in wild animal behaviour.