Country diary: The night air is thick with bats | Nic Wilson

Stevenage, Hertfordshire: They break the silence with their slaps, cracks and clicks - a reminder that unlit parks should be made safe for both humans and animalsIn the pitch-black night, Norway maples blaze orange on the far side of a blood-red lake. White bolts skim the ruddy surface of the water and flicker like St Elmo's fire round our heads. It's past 11pm, and we're observing the scene on Hertfordshire and Middlesex Bat Group's thermal-imaging cameras. My handheld monitor transforms the darkness into a multicoloured heatscape where common pipistrelles dart after midges and mosquitos, and Daubenton's bats fly low over the lake - level-headed hovercrafts to the pips' Hawk T1 jets.Our bat detectors fill the silent night with a hard rock soundtrack that could have been composed by a morse code enthusiast. Daubenton's bats rap out a rhythmic bassline with short bursts of staccato clicking. Above them, every pipistrelle has its own ultrasonic riff. With eight or more feeding simultaneously, they've adjusted the frequency of their echolocation calls (one proposed theory suggests this is to avoid confusion between individuals), and our detectors emit a syncopated chorus of slaps, crackles and pops. Continue reading...