In the Quiet of the Night: Counting Bats for Conservation

Catherine Blower is a passionate Conservation Officer who works for Natural Resources Wales. As part of her job, she is responsible for several Sites of Special Scientific Interest (SSSIs) that are important for their populations of lesser horseshoe bats. In this blog, Catherine shares her experiences of surveying these fascinating nocturnal creatures.

About Lesser Horseshoe Bats

There are two types of horseshoe bat in the UK; the greater and the lesser horseshoe bats. They are the only bats that hang freely upside down. You can distinguish them by size: greater horseshoe bats are about the size of a small pear, while lesser horseshoe bats are roughly the size of a plum. They are known for their distinctive 'fleshy nose leaves' (folds on the front of their faces) that help them use echolocation which is crucial for navigation and finding their prey. Lesser horseshoe bats hunt low to the ground, catching prey in flight and also by gleaning insects off the surface of vegetation. They mainly eat smaller insects like gnats, although they can also take moths and crane-flies.

Originally cave dwellers, they now have distinct seasonal roosting habits. In the summer, they prefer to use buildings with loft spaces as maternity roosts, whereas their winter roosts are typically in caves, mine shafts and cellars; environments with cool, stable temperatures that are ideal for hibernation.

In North Powys, we have many SSSI maternity and hibernation roosts that we monitor annually. Many of these roosts make up the Tanat and Vyrnwy Bat Sites Special Area of Conservation (SAC), but we also monitor non-designated roosts where the populations are linked to the SAC population.

The Excitement of Summer Surveys: Counting Bats at Dusk

Summer surveys are one of the highlights of my year. We generally count in June as we aim to monitor the adult population. Females give birth to one pup which are completely independent after six weeks, so a later count would get distorted by the additional juveniles. We usually arrive at our survey sites around 9pm on dry, calm evenings, just as the day begins to cool and the light softens.

The air is crisp against our skin, and there's a quiet buzz of excitement as we get into position around the known exit points of the roosts. We use bat detectors tuned to the frequency of around 109kHz, which help to pick up the first echolocation calls as the bats begin to stir within the roost. There's always a moment when the bats start to peek out, testing the light conditions before retreating back inside. This is an exciting time, as the anticipation builds and the team sharpens their focus on the exit points.

Once the first bat emerges from the roost and flies off, the chit chat stops and the serious counting starts! Using hand-held clickers, we watch as the whole roost empties in what seems to be an orderly fashion; one at a time to start with, and then in pairs, threes and sometimes more. It can actually be quite challenging to count each bat as it exits, which is why we usually need a team of three people so that we can take an average at the end.

It’s a breathtaking spectacle, particularly when the bats’ aerial acrobatics are matched with their unique calls on the bat detector. This intense period only lasts for about 30 minutes before the evening becomes calm and quiet once more. It's a brief but thrilling culmination of our preparations and anticipation.

The Quiet Vigil: Winter Bat Surveys

Winter surveys are very different but just as important.

These take place during the day in the lesser horseshoe bats’ dark and quiet hibernation roosts. We can find ourselves searching for hibernating bats hanging upside down off wine racks in cellars, or clinging to the rough walls and ceilings of disused mines.

These surveys are thrilling and adventurous, giving us the rare chance to explore places often off-limits to others. As we carefully move through these silent spaces, the cool, damp air and the hushed atmosphere make the experience almost ethereal.

Don’t be fooled into thinking it’s easier to count bats when they’re hibernating. They can cluster together in large numbers, making it difficult to pick out each individual. It also means we have to be careful not to count the same bats twice! We have to work fairly quickly in the hibernation roosts, so as not to linger too long and wake the bats out of hibernation.

The Value of Bat Surveys

Bat surveys are vital for understanding population trends and guiding conservation efforts. Although the number of lesser horseshoe bats in Wales has risen in recent years, ongoing monitoring remains crucial. These bats are confined mainly to western Britain and are particularly sensitive to disturbance, especially in their summer and winter roosts.

Many bat roosts are within buildings, which means we need to be in regular contact with property owners to ensure these sites are being looked after sensitively. Our survey data informs roost condition, habitat improvements and other interventions to support lesser horseshoe bat populations.

Monitoring also helps us spot sudden declines and understand the impact of a changing climate on this particular species. The data we collect feeds into Bat Conservation Trust’s National Bat Monitoring Program, helping to form a comprehensive picture of lesser horseshoe bat populations across the country.

 

About the Author

Catherine Blower is a Conservation Officer working across a suite of protected sites in the North Powys Environment Team. With a deep passion for wildlife and a commitment to preserving biodiversity, Catherine leads on organising the annual monitoring of key lesser horseshoe bat roosts within her patch.  Her wider work on the protected sites network includes working in partnership with private landowners to improve the condition of different habitats, including grasslands, woodlands and uplands.