National Trust sounds out speed dating for bats!
- Published:
- 03 November 2026
- Last updated:
- 03 November 2026
In late summer and autumn, hundreds of bats gather at Winspit Quarry in Purbeck, a nationally-important ‘swarming’ site for bats. We have been working with dedicated volunteers and high-tech equipment to find out more about this after-dark activity.
In an innovative high-tech approach to monitoring, we mounted a series of bat detectors in Winspit Quarry. These had sensors to pick up the ultrasonic clicks, squeaks and calls of the bats, which are largely at frequencies higher than humans can hear.
National Trust ecologist, Michelle Brown, said:
“Most of the bat activity is under cover of darkness, so it’s difficult to know how many bats are using the caves, and what species they are. The detectors will help us learn more, giving a broad picture of the range of species that pass by. It isn’t an exact science as some species have sounds that are too similar to distinguish them from each other, but it will give more information than we’ve been able to gather before.”
The detectors were removed last year, but it has taken some time to analyse the recordings – because the detectors generated almost 4TB of data! Firstly, cricket calls and other species were removed from the dataset, which left almost 150,000 files of bat recordings. Analysis was done with specialist software and expertise from the RSPB. The headlines from the findings are:
- The most recordings were from the common pipistrelle.
- Surprisingly, there was a high proportion of barbastelle bats, a woodland specialist species which is drawn to Winspit in the autumn swarming season.
- Amongst the rarest bat to be recorded was the grey long-eared, along with a number of greater horseshoes, our largest bat species.
The findings add weight to Winspit being one of the most important bat swarming sites in the country due to the number and variety of bats. Purbeck is home to 15 of the 17 bat species in the UK.
This data backs up the monitoring that volunteers from the Dorset Bat Group have been doing for the past 12 years. Working under licence, they trap bats in nets, measure them and record their size, weight and sex. They are then ringed on their forearms – previous tags have shown that some bats come to Winspit from as far away as 27 kilometres.
Michelle said: “We are hugely grateful to the bat group for all their hard work, which often involves being out on the windswept coastline in the cold and dark! We simply couldn’t do our work without the support of volunteers across Purbeck who help out with all aspects of wildlife monitoring and countryside management.”
Michelle also added a note of caution for anyone hoping to see a mass of bats.
“Autumn swarming is the term used to describe bats that gather at key locations to mate. We have different species swarming at different times, and the activity takes place in waves between dusk and about 4am. So there’s not a ‘swarm’ as such to see. Parts of Winspit Quarry are closed to the public for safety reasons, so we’d ask that people don’t go down there, especially at night.”
Bat studies and other initiatives are also taking place at inland quarries across South Purbeck. The aim is to put all the findings together then devise a strategy for bats across the region. This would involve connecting landscapes where they can spread and thrive, managing the land to increase insect numbers to feed the bats, improving existing roosting sites and creating new roosts.
