EcoNorth > EcoBlog > Species & Habitat Surveys > Bat Survey Season 2022

Bat Survey Season 2022

Bat survey season 2022 is just around the corner. If you’re keen to participate this year, read on!

Do you know your pipistrelles from your noctules? Have you ever wondered what PBRA stands for and what one entails? This blog will go over survey types, equipment and the bats themselves.

First things first – lets briefly go over the types of bat survey that we do at EcoNorth. There are three main categories. All are used to determine the presence of bats at a survey location, but each goes about it in a slightly different way.

Preliminary Bat Roost Assessments (PBRA)

Preliminary Bat Roost Assessments are what we use to find out if bats are using a structure to roost and to what extent it is/could be used. They can be undertaken at any time of year as the bats don’t need to be out and about – PBRAs look at the structures as well as for evidence of the bats themselves, so we can complete them even when bats aren’t active.

Usually, a PBRA will involve a licensed ecologist walking around a site during daylight hours and making a note of any structures, trees or other features with the potential to house bats, and the risk of this occurring. Suitable structures could be buildings, trees, bridges, bat boxes, cliffs – anything with cracks or little hidey-holes that bats could climb inside. These hidey-holes are referred to as ‘potential roost features’ and are what ecologists look for (along with signs of bats themselves) during the PBRA. Equipment used usually consists of binoculars, a good torch, and something to make notes with, along with an endoscope if needed. A camera is always handy too, as features can be recorded precisely and images included in reports.

The outcome of the PBRA will designate structures with a rating for bat use potential, and determine the number and type of surveys that need to be carried out next. Structures with negligible risk need no further work according to best practice guidelines, while low suitability structures require at least 1 further survey, 2 for moderate and 3 for high. These further surveys are activity surveys, and are covered in the next section.

Activity Surveys

Activity surveys are used to identify the number and type of bats in a given area, and how different areas/features are being used by bats; they can be split into two main types – Transects and Roost/Emergence surveys (often called Vantage Point/VP surveys). Both types of survey involve surveyors watching and listening for bats using bat detectors, and recording data for analysis at the office, but there are a couple of key differences.

Transects are undertaken to identify the bat activity levels in an area, so are ideal for identifying how bats use a particular site for foraging, commuting or other activity. Surveyors will walk around predetermined routes with their bat detectors and record any activity. Numbers, species and flight paths of bats are recorded. Transect surveys can begin at sunset, start a few hours before sunrise, or be undertaken throughout the night.

Roost/Emergence surveys are the type of activity survey we do most of at EcoNorth. They can occur at dusk or dawn, and entail a team of surveyors being positioned around a structure in a way that ensures all angles can be seen. Then… we wait! If the survey is at dusk, surveyors wait to see if any bats emerge from the structure, or return to their roosts if the survey is pre-dawn. Locations of emergences, roosts and any other activity in the area are recorded, and analysed at the office afterwards where needed. We can identify different bat species from recordings on the detectors, determine whether a bat has emerged from a building (eg if a surveyor on the north face of a building sees a bat, but the bat is not seen by a surveyor on the south, then it is likely that the bat has emerged from somewhere within the building rather than having simply flown over it), and use the data to determine how bats are using a roost at different times of the year. The outcomes of this type of survey are recorded in reports, and lay out the next steps that need to be taken for mitigation (if any).

A proportion of both types of survey ideally take place between May and August, with surveys running through the full active season, typically between April and September depending on the weather in the North East.

Equipment

Now, let’s get to grips with the bat survey equipment used at EcoNorth:

As discussed above, for PBRAs we can use binoculars, torches, endoscopes, cameras and recording sheets to assess and area, but for Activity Surveys the binoculars and endoscopes are swapped for thermal cameras and bat detectors. We have a few types in our arsenal, but here I will cover the most common, and the type you would be likely to use if you survey with us. We actually use a device called an ‘EchoMeter Touch 2 Pro’ – it’s a specialised microphone that can plug into most tablets and be used with an associated app. They’re very handy for a number of reasons, but one of the best is their user-friendliness – once the microphone is plugged in, the app will automatically record any bats it hears. This means that if anyone is unsure about details of the bat we can revisit the data at a later time to check what species was recorded. The tablet screen also means we can see the frequency and amplitude of bat calls visually, rather than relying on sound alone. Very handy, particularly for newbies! Some bats such as the pipistrelles show a classic ‘hockey stick’ pattern on the screen while others, such as Myotis species can show almost vertical lines, and we can even use the recordings to see whether bats are foraging or chatting to each other with social calls!

Bats

Finally, a look at some of the bat species we encounter at EcoNorth. There are 18 species of bats resident in the UK, but the following covers the 5 most common species or groups we encounter in the North East:

Name Call Rate Call Frequency (kHz) Description
Common Pipistrelle Moderate ~45 The UK’s most common bat, it is used by many as a reference to compare other species against. They can be found almost anywhere.
Soprano Pipistrelle Moderate ~55 As the name suggests, the Soprano Pip is a higher-pitched version of the Common. They are often found in the same areas, and particularly associated with areas of water.
Noctule V.slow ~20-25 A high-flying bat that typically lives in trees. Noctules have a very recognisable ‘chip-chop’ sound on bat detectors.
Myotis sp., including whiskered, Brandt’s, Daubenton’s and Natterer’s Fast ~30-120 The group of ‘Myotis’ species we find most often in North East England have very variable call frequencies, so can be tricky to identify for beginners. Watch for their rapid call rate and vertical patterns on the tablet.
Brown long-eared V.quiet ~35 The BLE can often be found in more rural areas, usually associated with areas of woodland or tree cover, and won’t normally appear until conditions are much darker. Their call has been described as ‘wet sounding’, and they’re very agile in the air.

 

Most bats in the UK are resident all year round, but hibernate during the colder months. Although bats are most commonly associated with night time, our activity surveys usually take place around dusk and dawn. This is a good time to catch them leaving a structure to feed and socialise, or returning after a hard night’s work. They exhibit four main types of behaviour: commuting, feeding, socialising and roosting.

Commuting is much like us humans going to and from work; the bats fly to a feeding area, and can regularly fly 2- 5km from their roost each evening. During this time, they call at slower and steadier intervals – using their echolocation to work out where they are and prevent any collisions in flight.

Feeding (also called Foraging) is where the real action begins, and calls become much more frequent. We can think of this as the bats increasing the resolution of their surroundings – more ‘pings’ from their echolocation will provide them with a more detailed picture of where they are, and what insects are there for them to catch. These fast-repetition feeding calls come in bursts, and can sound like someone blowing a raspberry on the detectors.

Surprisingly little is known about bat social calls and behaviour. They are often lower in pitch, but can be hard to distinguish from feeding calls at times. From my experience, some people record these and others don’t. The extra data is great, but not to worry if you’re unsure – we can always analyse further if required.

Bats leave their roosts at dusk and typically return at dawn, but the behaviour and things to watch out for on surveys are slightly different in each instance. Bat emergences can be tricky to spot as the bat only leaves once – you can sometimes hear them social calling, scratching or scuttling just before they take flight, but otherwise a keen eye is the best way to confirm an emergence. If you are on a dusk survey, it is a good idea to make a note of any possible emergence sites before any activity, as you’ll have some idea of where emergences might come from. It is also worth noting that emergences don’t always happen, so don’t worry if you don’t see anything! Roosts can be much easier to spot at dawn, as the bats often swoop up to a feature multiple times before deciding to land for good. These are called ‘False Returns’, and give the surveyor a good chance to see where bats are going. Bats have different types of roost for different occasions. Maternity roosts are where bats raise their young, hibernation roosts are used over winter and are more permanent, and day roosts can be used intermittently or regularly throughout the active season. Some species also use feeding roosts / perches, where they return several times throughout the night to eat larger prey like moths.

I hope that this blog has given you a bit of insight to the world of bats and bat surveys. It hasn’t covered everything, but it should be a good introduction for newcomers and a refresher for those who have worked with us before.

Would you like to participate with us on bat surveys in 2022? If you would, please feel free to contact me at alex.douglas@econorth.co.uk. No previous experience is necessary, the pay is good and they’re lots of fun. We’d love to hear from you!

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