Information about bats, as with other species, is necessary to understand the current status of these mammals and to allow us to support bat populations. In the latter half of the last century it was believed that bat populations, in the UK, were in decline. This was thought to be due to habitat loss, owing to factors such as change in agricultural practices and development. Speculation about the impact of these changes highlighted the need for more evidence and this resulted in the establishment of the National Bat Monitoring Programme (NBMP).
Why should we be concerned?
You may be wondering why we should be concerned about bat populations. Bats have a range of roles that help answer this question:
- Like bees, bats are important pollinators for some plant species. As well as chiropterophily, the term used for plant pollination by bats, they also spread plant seeds.
- In the UK all bats are insectivores – eating only insects - so help to control pests.
- Bats can act as indicator species – meaning that if there is a problem with bats this can indicate bigger environmental issues.
How can we monitor bats?
As bats fly around and catch insects, at night they use a high frequency system to navigate. These ‘echolocation signals’ make use of ultrasonic frequency. Bats make these calls as they are flying and then use the returning echoes to map their surroundings. Generally these are at a higher frequency than humans can hear, although it is possible to hear echolocation clicks from some bats. By using a bat detector the frequencies can be moved to a scale audible by humans. Using bat detectors allows us to differentiate between different species of bat . Listen here to the sound of a Pipistrelle bat, the most common UK bat, as heard with a bat detector:
Keoka - BY-SA 3.0
Much bat monitoring is carried out by volunteers who connect with national and international bat monitoring programmes. This allows understanding of bat populations and helps with the identification of bat species that require support or further protection. Indeed there is still much work to be done in understanding even the most common bats. For example, there is still little knowledge about how Pipistelle bats overwinter.
How can I monitor bats at home?
You can listen to bats using one of a range of different types of bat detectors. These vary both in what they do and price. Before investing, it is important to consider what you are intending to use the detector for. A simple heterodyne is a good starting point, so you can hear the calls. Heterodyne bat detectors convert the ultrasonic bat call into a sound which is audible to the human ear by shifting of one sound frequency to another. This type of bat detector allows you to listen to the bat calls when you are out and about so provides flexibility. As you get more interested you may like to advance the bat listening equipment you have – this could allow you to record the echolocation calls and even undertake computer analysis of them.
When using a simple heterodyne type detector, it is tuned in to a specific frequency, depending on the type of bats you hope to hear. Listen for different tones - different tones indicate different bat species. Regularly moving the frequency dial allows you to listen for diverse bats who make calls on different frequencies.
The Bat Conservation Trust provides a range of information and training relating to bat monitoring. This ensures that the approach used is standardised, enhancing the accuracy of the data collected. You can learn more about bat monitoring and share information through specific programmes.
It is important to remember that bats and their roosts, the places where bats live, are protected by the law. This limits what the general public can and cannot do in relation to bats. This includes the monitoring you are able to complete if you do not hold an appropriate licence. The Bat Conservation Trust provides more information on this. The overarching ethos is that non-invasive checks may take place without a license. Anything more, and certainly disturbing roosts or handling bats, needs an appropriately licensed bat worker.
Bats have different roosts, at different times of the year. For example in the winter they are found in a hibernation roost, whereas during the summer females move to a maternity roost. Bats do not make these roosts but use structures already in place. If there are few suitable roosts in your area you may want to create artificial roosts – bat boxes. You can make or buy these and they come in various designs. They require careful consideration in relation to their location. It can take a long time for bats to move to a new home, particularly if there is a large number of roosts locally. However, if there is a shortage of roosts they could move in within months!
What else can I do?
- If you have an hour to spare and would like to learn more about the greater horseshoe bat, and the challenges it faces, you can take part in a ‘virtual’ environmental field trip to Devon.
- If you would rather go out into the ‘actual’ environmental field, there are local bat groups throughout the UK.