Why bats treat our gardens as a larder

As the last colour drains out of the sky on a warm evening, something small and fast flickers across the lawn. Most gardeners miss it entirely. Once you know what to look for — or rather, what to listen for — it becomes very hard to ignore.

British gardens make excellent bat habitat. The mixture of open lawn, hedges, mature trees, ponds and generous flower borders supports the insects bats need, while the gaps between houses and along back fences create sheltered corridors for commuting between roost and feeding ground. No single garden is a complete bat reserve, but every garden with a decent hedge, a few trees and some water adds to a network that stretches right across a town.

All of our native bats eat insects. A common pipistrelle, our smallest and most familiar species, can take several thousand midges and small moths in a single night. That is a good argument for leaving one corner of the plot a little untidier than the rest.

What a bat detector actually adds

Bats are almost impossible to identify on sight. They move fast, they are active in near-darkness, and most of the useful detail lives in the ultrasound they produce for echolocation. A bat detector translates those calls into something audible, and it is the single most useful piece of equipment a curious gardener can own.

Most affordable models are heterodyne detectors. You tune a dial to a frequency, and any call near that frequency becomes a series of clicks, slaps or dry rasping sounds through a small speaker. It is a bit like tuning a shortwave radio: you sweep through the range until something appears. Full-spectrum and time-expansion detectors record the whole call and allow you to analyse it afterwards, which is more accurate but considerably more expensive.

What the detector gives you is not just a tick on a list. It tells you which species are present, roughly how many, and what they are doing. A pipistrelle working tight circuits over a border sounds nothing like a noctule powering high overhead on its way somewhere else.

The calls you are most likely to meet

Set your detector to about 45 kHz on a mild evening and you will probably hear these:

• Common pipistrelle — feeding clicks around 45 kHz, fast and rhythmic, often the first bat out and the last one back. Hunts low over lawns and borders.
• Soprano pipistrelle — very similar but peaking nearer 55 kHz. It tends to prefer water and woodland edges, so a garden pond may pull it in.
• Noctule — a big, high-flying bat with a slow, deliberate call around 20–25 kHz, sounding like a dry slap or a dropped pebble. Often seen at dusk, well above the rooftops.
• Brown long-eared bat — extremely quiet calls around 50 kHz, best heard when the bat is close. A moth specialist that gleans prey from foliage rather than chasing it in open air.
• Daubenton's bat — a steady, rapid rattle near 45–50 kHz, skimming low over open water. If you have a stream or a large pond, listen there.

Anything much higher, in the region of 110 kHz, would suggest a horseshoe bat — a genuine rarity and worth reporting. Do bear in mind that all British bats and their roosts are legally protected, so watch and listen only. Never handle a bat or disturb a roost.

Setting up a survey that works

A casual listen is lovely. A repeatable survey is far more interesting, because it lets you compare nights and seasons. Keep it simple and keep it consistent:

• Timing. Start about half an hour before sunset and run for an hour, or split the evening into fixed ten-minute listening points. Bats typically show a dusk peak and a second, quieter peak before dawn.
• Weather. Choose evenings above roughly 10°C, with little wind and no rain. Cold, wet and breezy nights are quiet, and a blank result tells you about the weather rather than the bats.
• Placement. Hold the detector at chest height, or mount it a metre and a half up and away from walls and foliage. Hard surfaces reflect sound and produce odd echoes that are easy to misread.
• Note-taking. Record the date, sunset time, temperature, wind and the frequency where each call sounded clearest. After a few weeks, patterns start to emerge.
• Repeat. Once a week through the season beats one long session in June.

Making the garden more inviting

If your detector tells you bats are passing through but not stopping, the habitat is doing the work and the food supply may not be. The fix is mostly about insects. Plant night-scented flowers such as honeysuckle, evening primrose and jasmine, and let a few native wildflowers go to seed. Avoid broad-spectrum insecticides, which remove the prey base as effectively as they remove the pests.

Water is a powerful draw. Even a small pond, sunk so that the edges slope gently, will bring in insects and give bats somewhere to drink on the wing. Hedges and climbers create sheltered flight lines, and mature trees provide both roosting opportunities and a supply of moths. Finally, cut unnecessary outdoor lighting. Security lights and floodlit facades fragment commuting routes and make bats far more vulnerable to predators. Use warm, downward-facing fittings with timers or motion sensors, and keep them off the flight lines along hedges and water.

Reading the season in the dark

Bat activity in Britain runs roughly from April through to October, with the busiest months usually falling between May and September. Early in the season, expect brisk feeding as bats recover from hibernation. Midsummer brings the maternity colonies out in force, and the calls can be relentless over a good garden. By late summer and early autumn, you will often hear the slower, more erratic sounds of juvenile bats learning to hunt, followed by a final flurry of feeding as insects fatten up before winter.

Keep your records going year on year, and pass them to your local bat group or a national recording scheme. Those small, ordinary observations of a common pipistrelle over an English lawn are exactly the kind of evidence that shows how our gardens are holding up as wildlife habitat — and where they need help.