MARTYN ROBINSON trains his sights on the pebbles peppering our stony deserts to see what he can spy
Camouflage is vital for many animals to survive. It needs to be a fairly accurate copy of whatever it represents, as getting the wrong texture, shape or size will attract attention. One disguise that is very hard to pull off is mimicking a pebble, but some Australian animals manage this trick. The top three for me are a bird, a grasshopper and a lizard. All live in arid zones on gibber plains, also called desert pavement, where the ground is covered with shiny, ironstone pebbles, ranging from the size of a fist down to a thumbnail.
Although quite visible in this image (above) even the gibberbird (Ashbyia lovensis) can ‘melt into the background’ as soon as it crouches motionless among the gibbers. Males and females, which are very similar, don’t appear at first glance to be good mimics of the gibbers, but try to keep your eye on them in their natural pebbly habitat and they seem to vanish.
Meanwhile, the gibber grasshopper (in the Acrididae family) matches the lustre and shape of the pebbles so well that unless one happens to hop, the chances of noticing it are remote. When danger threatens, these clever grasshoppers have another camouflage trick: they curve their abdomens to one side to present a less symmetrical shape in a bid to match the gibbers.
But the best of the three disguises has to be the tiny pebble dragon (Tympanocryptus cephalus). Like the grasshopper, this reptile matches the gibbers in colour, shape and lustre, but it has an extra dimension: its tail, which could ordinarily give it away, looks like a twist of dried grass.
Now you may wonder why these three animals have evolved to look like gibbers, given how hard it must be to remain motionless all day. The gibber plains have very little vegetation, so anything hiding in the plants is easy for predators to find. But, with gibbers everywhere, predators don’t know where to start searching for those few gibbers that aren’t what they seem.
Martyn gardens mainly on Sydney’s Northern Beaches
Have you found something interesting in your garden? Send us a photo and Martyn will ID it. Email email@example.com with ‘Creature’ in the subject line.