Learning bird song is straightforward enough: go outside, listen to birds. Then watch birds. Start to put the senses together. Which bird says what? That sweet, happy-yet-wistful song any time of year is a robin, that harsh screech a jay, the strident chiff-chaff-chiff-chaff in March is – guess what – and the gentle hueets moving through a low tree canopy six months later are contact calls from the same species. Birds are only a part of nature’s soundscape, though. They’re often the dominant one, but it depends on where in the world and when in the day or year you happen to be listening.
At night, it’s often other creatures that rule the acoustic roost, inhabiting a secret world of sound that can be a little trickier to unlock. That might be because it’s a sound world predominately outside of human hearing range, as for super-squeaky bats. Fortunately, access to their secrets can be bought with a little help from a bat box, which I and the other Reading staff and students on the recent Devon field course very much enjoyed playing with. We started one evening by lying in wait for a roost of lesser horseshoe bats, which use very high frequency sonar they amplify through strange, leaf-like appendages on their nose. The sound is fantastical, an almost machine-like wavering whistle that is markedly alien. Making more conventional rapid clicking sounds were diminutive pipistrelle bats, accompanied by near identical soprano pipistrelles – a separate species mostly told by its higher frequency calls.
Our bat boxes also picked up numerous crickets, though most of them were loud enough to be heard unamplified, which opens for discussion the other tricky element of night sound: insects. Big, noisy ones like the great green bush cricket thrive in the relatively mild year-round climate of the far south coast, such that the late summer nights – and days – in south Devon have a notably more Mediterranean feel than relatively quiet Berkshire. Our week was blighted by rain and often chilly, but the crickets seemed unfazed, chuffing and chirring away whatever the weather. Nonetheless, the intensity of sound seemed to fade as the week went on. One by one the crickets died off, fell silent, and dropped out of the chorus, until just a gentle murmur was left to trail into autumn.
By way of contrast, a few days later I stepped out of a car in the mid-Atlantic United States, to be met by a cacophonous wall of natural sound. Late summer in that part of the world is scored by a musical assembly of crickets, katydids, cicadas (largest and loudest of the homopteran bugs by several orders of magnitude) and tree frogs. It’s a seemingly impenetrable collision of scrapes, croaks, reels, fiddles, taps and clicks that I’m hardly beginning to unpick into separate voices (though I did just stumble on this excellent website, which should help!), whereas the few active cricket species down in Slapton were relatively quick and easy to learn.
Such a contrast with Reading’s relatively empty soundscape, or even Devon’s gently active one is perhaps not too surprising. Our destination in the state of Maryland is roughly on the same latitude as Rome, so one might expect a warm-climate fauna to predominate. But the winters get cold, colder than they ever would in Reading, Devon, or indeed Rome. Much of the natural history of this land of contrasts is still beyond my understanding, but however it is produced and sustained in a fairly harsh climate, the audible biodiversity of late summer in America is surely a magnificent thing.
I can’t help but wonder just how much more magnificent it may have been in the relatively recent past. Since the collapse of large-scale commercial agriculture in many of the eastern states, second-growth forest has reclaimed a lot of land, only to see it fragmented again as frankly quite ugly housing developments and new ‘shopping plazas’ take bites out of the newly-grown woods. The deafening roar that greeted our ears was emanating from habitats that are far from pristine and that, as far as I can see, are more degraded each time we visit. The din which arose from the Atlantic forests before the first European settlers arrived must have been incredible.
So it’s hard to know what the future holds for natural sound. In his intriguing book The Great Animal Orchestra, ecologist and musician Bernie Kraus argues that natural soundscapes are complex tapestries in which each noise-making animal has carved out a niche over eons of ecosystem evolution, and are therefore a key way of rapidly assessing the health of that system. That’s easy enough to grasp when thinking about the dawn chorus of songbirds, especially since we more often see the song-maker and can draw a connection between its disappearance and the cessation of its song.
Perhaps because the majority of our native insects (frogs and bats too, if you like) in Britain are on the quiet side, at least as far as human hearing range goes, I hadn’t often thought of non-bird sound as so integral a part of nature’s choir. It’s feasible it will become more evident here as climate warming encourages the spread of bigger, showier insects, as already seen with some of the bush crickets. The moderately loud August evenings enjoyed by residents of Slapton could yet be coming to suburban Berkshire, whilst elsewhere in the world habitat destruction could well usher in quieter nights instead. In this way soundscapes are another demonstration of the unpredictable havoc humankind is playing with the natural world, and the successful nature conservationist will be one who continues to keep his or her ears open.