We are standing around outside a medieval bishops' palace clutching bat detectors, an impatient group of Londoners watching the sun set. We adjust our detectors to 50kHz and head off into the quickening darkness of Fulham Palace behind our London Bat Group guide John Tovey. We are in search of the common pipistrelle, London's best known bat.
Finding London's bats
Bats are almost everywhere in London, living in the nooks and crannies of our homes, walls and woodlands. They've taken up residence in an abandoned railway tunnel in Haringey and the gardens of Buckingham Palace. They thrive at the London Wetland Centre and in other parks and conservation areas. They come out at night to feed on insects over wetlands, parks, rivers, compost heaps and anywhere that bugs fly. They weigh 3-5g, have a wingspan of up to 25cm, and fly around at 10 kilometres per hour (6 mph). The dark-brown common pipistrelle is not easy to spot against the night sky. They are noisy critters, shouting out to echo-locate their prey, but in one of evolution's greatest accommodations, bats' ultrasonic calls aren't audible to human ears.
Which is where the bat detectors come in. Wandering around the grounds of a bishops' manor house at night staring up into the darkened treetops for signs of life does hold some appeal. If you are really interested in bats, however, then it is best to listen out for them. The bat detectors convert ultrasonic bat calls into a frequency within human hearing range. With microphones pointed upwards we were able to listen in to pipistrelles hunting down insects at the start of a long night of feeding.
Bat life and threats
It is hard work being a bat. As John our bat guide tells us, flight is a very energy intensive way to get around, and little bats with tiny mouths, like the common pipistrelle, put a lot of effort into finding and catching midges, mosquitoes and other small insects. During the summer breeding season female bats take their new babies with them. The young cling to their mother's fur while she flies around eating for two. She works under the added pressure of producing milk while meeting her own needs for nourishment (and before you ask, bat milk macchiatos are not a thing, not even in Shoreditch).
Bats and their roosts are protected by law. After a century of decline, numbers for most species in the UK have now stabilised or increased. Still, finding a place to live in London is not easy for the average bat. Demolition of old buildings can spell eviction for colonies and shiny new buildings often lack the little gaps needed for bats to settle. Lights left on at night can disorientate bats and their prey, and new urban development fragments corridors of green space that the creatures travel through. Domestic cats prowling at night are also a major hazard for bats and the leading cause of workload for London's network of volunteer bat carers.
Making London bat friendly
The Bat Conservation Trust works in London with developers to provide monitoring and advice to make city living easier for bats. With the Victoria Business Improvement District they've been identified five different species in a busy central location, including the relatively rare Nathusius' pipistrelle and Leisler's bat, along with the common pipistrelle. Green roofs, green walls, wild flower meadows, bat boxes and green infrastructure in buildings, developments and parks help to provide habitat for bats and the insects they eat, while also making the city a nicer place for us humans to live.
Want to find out more about bats near you, or become involved in their conservation? Here are five ideas:
BAT DETECTOR: Buy, build or hack your own bat detector. The Bat Conservation Trust provides advice on various bat detectors on the market, or build your own from simple electronic components. With some tweaks, you can use your smart phone to visualise bat calls to help with identification.
REPORT A BAT: The Big Bat Map records bat sightings across the UK, and provides some advice on where to go to find bats in your neighbourhood.