Summer frog-song and the wet

For most of the year the wallum swamps and the floodplain wetlands are quiet places. Then the wet arrives — the warm, storm-fed months from about December — and on the first hot, wet nights the whole low country finds its voice. Stand near a paperbark swamp or a wallum hollow after dark in a summer downpour and the noise is astonishing: the deep banjo bonk of the pobblebonk, the sharp tok of the striped marsh frog, and layered under them the thin calls of the small frogs, each species holding its own line in a chorus you can hear from the far side of a paddock. It is the single loudest thing the coast does all year, and it lasts only as long as the warm rain keeps coming.

Some of the callers are ordinary frogs having a good night. But down in the sour, tea-coloured water of the wallum swamps are the ones worth crossing the region for: the acid frogs, a handful of specialists that have evolved to breed in blackwater so acid it would kill most frogs’ eggs outright — water down around pH 3.5, roughly as sour as orange juice. The acidity is not a hardship they suffer but a wall they hide behind, because it shuts out most of the predators and competitors that would otherwise strip their spawn. Their breeding is tied to that sour water and to the warm-wet trigger together, which is why the summer chorus in the wallum is not just louder than elsewhere but genuinely rarer — you are listening to animals that live nowhere else on Earth.

And the rain is doing a second, invisible job while the frogs sing. Every summer storm that soaks into the sand is topping up the huge freshwater sponge held inside it — the aquifer that will keep the swamps wet, the blackwater flowing and the acid-frog nurseries alive right through the following dry, long after the storms have gone. That is the quiet bargain of the wet season on the sand coast: the noise you can hear on a summer night is paid for by the water you cannot see soaking away beneath your feet. Christmas bells hang out their waxy red-and-gold trumpets in the wet heath toward the turn of the year, the frogs roar, and the country lays in the water it will spend for the next twelve months.