Bat Survey Method

The objective of this project is primarily a census and activity mapping exercise, so the survey methods usually employed have been adapted to suit.

I used a constant speed walk because I don't want to distort the data by loitering in an area and increasing the temporal probability of recording a call. The recording time was restricted to a maximum of 2.5s, since this reduced the probability of introducing errors in the geo-tagged location of the call, which is what would happen if there is a significant amount of bat activity and a long recording preset time.

The final optimised transect plan is given in the image below. These were the core routes, and random excursions were also employed to sample away from the path/bridleway/ride edge where possible to improve the probability of detecting the quiet calling Plecotus family and the bechsteins's bat. In addition, no transect was started from the same place at the same time to minimise any temporal correlation in the presence sightings.

The field areas were covered using a "lawn-mower" transect pattern with a 25m pitch.

I worked with night vision goggles since this minimises the level of disturbance to the other wildlife, but it does place a premium on knowing the forest well as the forest looked very different when under night vision! Also, if you ever intend to use night vision goggles, make sure you get some practice in a safe area you are familiar with... Using them initially is quite disorienting, and it takes time to get used to the limited field of vision and depth of field.

Since I was trying to establish presence and activity areas, I'm not going out when the probability of detection is going to be low. So, typically the ground windspeed had to be below 20mph, and the dusk temperature greater than 10 degrees C. If you look at Google earth you'll also see that a great deal of the western edge is new plantation or partly cleared, so not good bat habitat.

The beauty of the Elekon BatLogger is that all the call recordings are geo-tagged from a built in GPS, and a record of the ambient temperature is also taken. This makes identification of the precise location and time of the recording possible, and essential for this sort of survey. All my times are recorded in UTC as it avoids confusion over daylight saving time changes.