Much like nature photography, bat work requires patience, determination, and the ability to sleep whenever your schedule allows. Dawn/Dusk surveys can be mentally taxing; however, bat surveys offer you the opportunity to get to know some of the UK’s rarest and most elusive species. Temple ecologist Harry Jarvis takes us through what life is like in the dark, giving an overview of what life is like as a bat worker.
The aim of a bat survey is to determine if a building or tree is home to an active bat roost and if the surrounding environment provides a notable habitat for bats. The best way of inspecting a roost is to endoscope a feature and see if there’s anyone home. However, this isn’t always possible, and the next best option is for a surveyor to observe a roost from ground level during key emergence/re-entry times.
A bat survey can take some considerable planning, and if it’s an awkward building with many potential roost features, there may need to be several people on a survey. Planning for a survey usually takes place well in advance starting with the survey lead familiarising themselves with the site, and ensuring they understand the main bat features. Different features can attract different bat species, for example, features leading to an enclosed loft can attract larger roof-void dwelling bats, whereas cracks on the outside of buildings can be more attractive to smaller crevice dwelling bats. A good understanding of the site allows you to plan meeting times, positions, start and finish times, and pinpoint the main foraging habitats. Planning in advance can lead to a successful survey, however, unpredictable weather can interrupt surveys. Strong wind, precipitation, and temperature can all affect the likelihood of a bat emerging from its roost, and planning for this can stop a wasted survey effort.
Carrying out the surveys is a relatively easy task. We meet on site around half an hour before sunset to set up our surveyor positions, bat detectors, and infra-red cameras. The survey starts 15 minutes before sunset and bat workers will observe a feature waiting to see if a bat emerges. If a bat does emerge, we take notes and times to analyse after the survey. Alongside watching for emergences, surveyors must keep an eye out for foraging or commuting bats as this can indicate areas of significant importance to bats. Surveyors will usually finish 105 minutes after sunset to ensure all emergences have been observed. The same process is used for a dawn survey however start times will be 105 minutes before sunrise and finish times will be 15 minutes after sunrise. The techniques used in a dawn survey are the same as dusk, however, re-entries are usually easier to spot as bats often flutter around their roost before resting for the day.
The data we collect is usually in three parts; the observational data from the surveyor, the infra-red camera footage, and the recording from the batlogger (batloggers record the ultrasonic echolocation calls from bats and convert them into audible sounds). All three information points support one another and allow the data analyser to determine the species, activity type, and population statistics. These results inform our clients on how significant their site is for bats and what licences they need to acquire before work can be allowed. This data can also be used to develop mitigation plans if developments are planning to disrupt bat activity.