Sue M writes:
I have detected far more crickets than bats with my bat detector recently. On a recent walk near Ascott under Wychwood I pointed it, set at about 20kHz, at a sunny field edge and heard a continuous buzzing, rather like the noise you can hear near an electricity pylon.
There weren’t any pylons in sight, so we hunted around to see if we could find what was making the noise, and soon found a male Roesel’s Bush Cricket. These handsome beasts are quite obliging and often sit on leaves for long enough to be photographed. We could clearly see its short wings vibrating as it sang, and the recording is the sound that the bat detector made audible to us.
For contrast, here’s a recording of a male Speckled Bush Cricket singing in my garden. The loud clicks were recorded with my bat detector set at about 40kHz.
The song of a Dark Bush Cricket can be found here.
The noises made by grasshoppers and bush crickets are usually referred to as a “song”, even though in some cases they aren’t particularly musical. A full spectrum recording would reveal a far more complex sound, but my bat detector isn’t up to that. Full spectrum recordings can be heard here on the internet (where else?).
The main picture is the common short-winged form but there is also a rather uncommon long-winged ‘diluta‘ form which develops when there is pressure on the population and they expand their range – presumably because they can fly further. Because the wings are longer one would expect their song to be at a lower frequency, and possibly audible without a bat detector but we’ve yet to see and hear one singing at the same time.
John C adds: We seem to hear many fewer grasshoppers and crickets than we used to. That may simply be because our hearing deteriorates with age, or there may be fewer of them. However, a walk with a bat detector is revelatory and adds an extra dimension – they are still there and, although bat detectors are not very ‘directional’, it’s possible to home-in on them to within a metre or so. After that it’s a matter of searching, not too difficult once you get your eye in. Passersby generally give us a wide berth and funny looks when we’re doing this, although perhaps one in ten or twenty of them ask what we are up to and seem genuinely interested when we explain.
For a bit more on the long-winged form of Roesel’s Bush Cricket in Oxfordshire watch this short video by Richard Comont.