Emily Hartley
Why dusk is the best time of day
As the light drains out of a summer evening, British bats are just waking up. All eighteen of our resident species are insect eaters, and dusk is when the moths, midges and caddisflies start to stir. The first bats usually appear around twenty to thirty minutes after sunset — sometimes earlier on warm, still evenings — and the busiest half hour is often an hour after the sun has gone.
You do not need much kit to enjoy this. A bat detector, a red-filtered torch and warm clothing will do it. The detector matters most: bats call at frequencies far above human hearing, so without one you are watching silent silhouettes. A basic heterodyne detector is the traditional beginner's choice. You tune it to a frequency, and it plays back a rough version of the bat's echolocation call as audible clicks, slaps or chirrups.
Timing is everything. Choose a dry, mild evening with little wind — below about 10 mph — and avoid nights after heavy rain, when insect activity drops. May to September is the season, with July and August the peak.
Choosing a spot near water
Water is the beginner's secret weapon. Ponds, canals, slow rivers and lakeside paths hold clouds of insects and give bats a clear, open flight lane. Water also reflects sound well, which helps bats hunt.
Look for a stretch with a few different features close together:
- Open water, for species that fly low over the surface.
- A hedge, tree line or lit building nearby, for bats that prefer edges and clutter.
- A lamp post or two. Insects gather around lights, and hungry bats follow.
- A bench or bank where you can sit still and stay out of the way.
Sit quietly for a full twenty minutes before you expect anything. Bats are quick to notice movement, and your own eyes need time to adjust. Early on, watch against the pale western sky — silhouettes show up beautifully before the darker water gives you any help.
Hearing your first pipistrelle
Pipistrelles are the bats almost everyone meets first. They are small, fast and fluttering, tumbling around tree tops and street lights like scraps of burnt paper. Most are common pipistrelles, with soprano pipistrelles a close second.
On a heterodyne detector, set your dial to 45 kHz for common pipistrelles. You will hear a rapid, rhythmic smacking — often described as wet slaps or a fast "chip-chop" — repeating several times a second as the bat closes on prey. Sopranos are best picked up around 55 kHz and sound similar, just a touch higher and thinner.
If you are unsure, try slowly sweeping the dial rather than jumping between frequencies. The call will swell to its loudest, clearest point when you are tuned close to the bat's peak frequency. Note the time, the species and the weather in a notebook; patterns build quickly over a season.
Daubenton's bats and the art of trawling
Daubenton's bats are the water specialists and, for many people, the stars of a dusk watch. They are medium-sized and dark, with a pale belly, and they fly low and straight over the surface, sometimes dipping a tail or wingtip to snatch insects from the water itself. Naturalists call this trawling.
They tend to emerge later than pipistrelles — often forty minutes to an hour after sunset. Tune your detector to 35 to 40 kHz, and listen for a very fast, steady series of dry clicks, like pebbles rattling on a path. Look for a bat skimming level over open water, holding a straight line, occasionally touching the surface and then carrying on.
Because Daubenton's bats stay over water, they are the easiest species to watch with a torch. On a calm evening you can follow one for a hundred metres or more along a canal or river.
Torchcraft and bat-friendly etiquette
Use a red filter over a low-powered torch. Bats are far less sensitive to red light than to white, so you can watch without blinding or disturbing them. Keep the beam low and wide, sweep slowly, and never hold it steady on an individual bat for long.
A few simple rules keep everyone happy:
- Never shine a torch at, or approach, a roost. Bats and their roosts are protected by law, and disturbance can be an offence.
- Do not touch a grounded or injured bat. Call your local bat group or a wildlife rescue for advice.
- Leave handling to licensed bat workers.
- Keep noise down and keep dogs on a lead near the water's edge.
Keeping a simple record
A small notebook turns an evening's watching into something genuinely useful. Note the date, sunset time, temperature, wind and cloud, then the species you heard or saw with the time of first and last contact. Even a first pipistrelle at 21:15 is a data point.
Within a few weeks you will start to recognise your own local bats by sound alone, and to notice how much they shift with the weather. That is the real pleasure of dusk watching: a quiet bank, a red torch and the sudden slaps and clicks of bats going about their nightly hunt above your head.
