April 2015 On Friday 17th April the barbastelle bat tracking team assembled again. Meeting at the Yarner Woodland Centre, 25 eager volunteers listened to Andy Carr of Bristol University introduce the more technical aspects of the forthcoming study.
The barbastelle is undoubtedly rare, estimated UK numbers are around 5000, and there are many significant gaps in our knowledge of the species including the variations in their behaviour throughout the season. If enough data is produced the survey should provide information on how their foraging habits change before and after young are born. It will pinpoint their roosting trees and monitor the use of roosts relative to seasonal feeding sites. Together this will inform the Woodland Trust and Natural England how to better manage the woodland in the Bovey Valley with the bats in mind.
There are three planned periods of surveying, the earliest starting as soon as the bats are trapped, tagged and released in April and May. They will be left alone during June as heavily pregnant females and dependent young should not be disturbed. After that, two more study periods through the summer and autumn should establish enough information to understand barbastelle foraging behaviour in the Bovey valley. Also, alongside the monitoring of night time foraging, the volunteers will spend six months locating the daytime oak tree roosts to assemble the most comprehensive information.
An array of bat tracking equipment for the volunteers to learn how to use
Andy’s talk continued, introducing the trainees to the equipment used in radio tracking of wildlife. Hand held devices included the directional aerial and receiver which would be set for the unique frequency of the tag on the bat being monitored. Subtle changes in the bleeping signal will, with experience, allow the volunteers to work out 5 to 6 “fixes” or location readings every hour through the night. All the location data will be collected on a trimble GPS device set up with “cyber tracker” software. Other, less specialised equipment will include a good pair of boots, layers of clothing and a car …. or a batmobile!
Night time tracking is usually done in reasonable weather as most mammals would agree that staying inside on a wet Dartmoor night is a good option. As a result, both human monitors and bats will have a higher chance of being out on the same night. A typical night will start around 30 minutes before sunset, meaning short nights in July and longer shifts in September. Volunteers will work in pairs, sharing the driving, navigating, tracking and plotting duties. There won’t be many opportunities to rest but when the bats are busy foraging they will stay in a good feeding site. The trackers will need to stay awake though … the bats could move on at any minute and the volunteers will need to keep up with Barbara, Stella or Bobby (the bats will all be named).
The future success of the barbastelle is uncertain as it is a “niche” bat, a specialist. It feeds on particular moths, some of which can hear and evade a loudly echolocating bat so the barbastelle skillfully keeps the volume down. It also roosts in cracks and crevices in old oak trees as a preference, so roosting sites need to be found and plotted. As the tags will transmit during the day the volunteers will be able to find the roosting bats.
After all the roosts are located the final part of the survey can go ahead. Emergence surveys should provide information on social structure and show which members of the colony roost where, and which start foraging first. It’s a complicated picture but it will all emerge over the summer months, once the volunteers have completed their training. Now the signing-up process begins before the practical training continues next week.
To read the complete series of Barbastelle Tracking Diaries:
Words and images for the Barbastelle Tracking Diary are by Matt Parkins
The Bovey Valley barbastelle tracking project is managed by the Moor than meets the eye Landscape Partnership comprising Dartmoor National Park Authority, the Woodland Trust and Natural England.