The Australian wallabies that love our rocky mountain ranges
Why does Australia have wallabies that love rocks?
Tim Low lives in a state of perpetual surprise at everything wild and alive. His response is to write searching books, Australian Geographic articles and this blog. His book Where Song Began (Penguin, 2014) recently became the first nature book ever to win the Australian Book Industry Award for best general non-fiction. Tim’s newest book is called The New Nature.
ONE OF THE thrills on offer in Australia is the sight of rock-wallabies bouncing off rock faces as they bound away. Their fearless agility is breathtaking, with leaps that recall the flight of a ball in a lively game of squash.
To the city dweller they can seem like oddities, but Australia has far more species of rock-wallaby – 17 – than of other mammals that hop. But that means less than it seems, for Australia has many more individual kangaroos than rock-wallabies. Rock-wallabies are divided up into more species because populations isolated on different mountain ranges have evolved into separate species, some of which are rare and none of which are truly plentiful.
Why should these wallabies be committed to rock? During hot summers and droughts shady recesses on outcrops limit heat stress and water loss. Steep slopes deter predators. And rain shed by rocky slopes can produce lush growth below.
But many rock-wallaby colonies are doing badly today. Foxes are breaching many of their craggy fortresses and feral goats and livestock grazing below outcrops are taking their food.
In Kangaroo Valley in the Shoalhaven area Juliet Dingle of the NSW National Parks and Wildlife Service took me down a small cliff near the river and pointed out ‘Blazey’ watching us from a small rock ledge hidden behind rainforest vines. A colony of about 30 brush-tailed rock-wallabies is surviving around here, but only because foxes are poisoned and shot. The Friends of Brush-tailed Rock-wallaby group, active here for two decades, encourages landholders to support fox control, without which any young wallabies disappear soon after they leave the pouch.
A black-flanked rock-wallaby in Kangaroo Valley. (Image Credit: Christopher Watson)
In the western half of Australia the black-footed rock-wallaby stands out by having a vast domain. I have seen them around Alice Springs and on North West Cape on the Western Australian Coast. They live on outcrops in the Wheat Belt inland from Perth and on islands in South Australia. Rocks are far from continuous in these regions so it is unclear how this species has spread so widely.
Australia’s deserts are younger than many species living in them, and one possibility is that low connecting outcrops of laterite have eroded away or been buried under sand. This scenario has been offered to explain why pebble mound mice, which also need rocks, have big gaps in distribution.
Wombat burrows provide another possibility. On Wedge Island in South Australia, rock-wallabies often shelter in the humid burrows of hairy-nosed wombats. Tens of thousands of years ago wombats lived far into the Outback and their burrows could have helped dispersing rock-wallabies move across sandy plains. Trees with angled trunks are also used at times by some rock-wallaby species.
But rocks are what these wallabies are really all about. In some of Australia’s rocky places these charming animals are easy to approach. Magnetic Island teems with them, as does a nature park near Mareeba. There are also good viewing sites around Alice Springs, including the Olive Pink Botanic Garden, where I sat by the cafe and watched one browse a garden bed less than two metres away. It made my day.