Loud and proud

0

Can you describe the sound of the African bush? Cliché demands such timeless classics as the majestic roar of the lion or haunting cry of the fish eagle. But just close your eyes and listen. Behind the greatest hits is a chorus of clicks, grunts, yelps, barks and whistles – all of them meaning something to somebody. Mike Unwin zeroes in on a few of Africa’s more notable noisemakers.

Frog-shutterstock_2695214Frog chorus
No visitor to an African wetland during summer can fail to be impressed by the amphibian symphony that gets underway at sunset – especially following rains – as the frog chorus tunes up. Some species sing high, some low; some mutter erratically, others chirp relentlessly. Combined, they can swell into a pulsing wall of sound, amplified by the singers’ balloon-like inflatable vocal sacs. These calls, just like bird song, enable males to claim territory and attract females. Listen carefully and you can pick out each singer by its unique voice: the irregular liquid quoip! of the bubbling kassina (Kassina senegalensis) sounds like a single heavy raindrop; the shrill whistling chorus of painted reed frogs (Hyperolius marmoratus) recalls a string section from Pyscho; the collective rhythmic bleating of snoring puddle frogs (Phrynobatrachus natalensis) could be the honking of distant geese. Spotting the singers, however, is a different matter.

Flexing the abs 
As midday temperatures rise, so most animals tend to save their energy by falling silent. But not cicadas, whose relentless zinging buzz seems all the more ear splitting in the oppressive heat. These boggle-eyed insects belong to the bug family (Hemiptera), and there are about 450 species across Africa. It is the males that make the sound. They do not stridulate (rub their legs or wings together), as do crickets. Rather they repeatedly contract and relax special rib-like modifications on the base of their abdomen, called timbals, to produce a series of sharp clicks. Done at high speed this becomes a continuous stream of sound and is amplified by the largely hollow abdomen. Males can disable their tympana – the bug equivalent of ears – while calling, which is just as well, as some species can crank up the volume to 120 decibels. Each species of cicada has its own distinctive song to attract the appropriate mate.

The language of fear
Life on the African savannah is nothing if not hazardous, with hungry predators at every turn. Vervet monkeys, like many social creatures, use alarm calls to warn one another of danger. Unusually, however, they use different calls to distinguish between the different forms of danger – and so can respond accordingly. Thus when one individual gives the ‘snake alarm’, all the other troop members will immediately stand on their hind legs and scan the long grass for a lurking python; a ‘leopard alarm’, by contrast, will have them rushing into the outer branches of the nearest tree, out of reach of the big cat; and an ‘eagle alarm’, different again, will send them plunging into thick foliage, safe from an aerial strike. Things presumably become more problematic when the three predators arrive together.

Non-movers and shakers 
As dusk falls across the Kalahari, an odd clicking sound fills the air. It comes in short bursts, like the periodic shaking of a matchbox. Not loud, but persistent. You trace the sound to a nearby patch of ground. But it stops abruptly when you approach – only to reveal another taking up the refrain a little further away. The more you listen, the more you hear: the matchbox shakers seem to have you surrounded, their weird chorus stretching to the horizon. These – believe it or not – are the calls of male common barking geckos (Ptenopus garrulus). Thousands of them. This unusually vocal reptile emerges at sunset to proclaim its territory from the mouth of its burrow. The largest males, which are the most successful breeders, have the lowest-frequency calls. Thus rivals can check one another out across the airwaves without having to venture out into the dangerous darkness.

It takes two
You’re minding your business in the bush when a piercing noise erupts from a nearby thicket: a pure, bell-like whistle followed, instantaneously, by an ugly, grating growl. It sounds like one single utterance, except that the whistle comes from your left and the growl from your right. Moments later you hear it again – exactly the same thing. Is it one bird or two? Is it a flute-playing ventriloquist with laryngitis? In fact what you’re hearing is the perfectly synchronised duet of a male (the whistle) and female (the growl) boubou shrike. This skulking species maintains a year-round territory in dense bush and has evolved duetting as a means for male and female to keep in touch. The timing is so perfect that to our ear it often sounds like just one bird.

 

First published in Travel Africa magazine, Edition 45, Winter 2008/9

Share.