PHOTO: A koala sleeps in a tree in the bush, January 2013.(Flickr: Degilbo on flickr)
The iconic koala is renowned as a nocturnal tree-hugger that sleeps a lot and is fussy about which eucalyptus leaves to eat.
However, the latest research suggests efforts to save koalas from extinction by protecting their habitat may be barking up the wrong tree.
Dr Matthew Crowther from the University of Sydney questions the efficacy of koala management plans that focus solely on preventing the loss of food trees or restoring food species habitat lost to development.
“It is not just food species – you have to have a combination of trees that have thicker foliage,” he said.
“Also – and this is a bit more controversial – the shelter trees need to be bigger trees, and trees don’t grow overnight.”
Dr Crowther has led a team, including scientists from the New South Wales Office of Heritage and Environment, the Australian National University and Murdoch University, that has been analysing three years’ worth of data from Global Positioning System (GPS) tracking collars on koalas around Gunnedah in north-western New South Wales.
The research suggests koalas are using different types of trees at night from those they use in the daytime, and often trees in which they cannot feed.
“In Gunnedah they can be in casuarina trees, they can be in kurrajong trees, not necessarily trees that they like to eat from,” Dr Crowther said.
The research, published in the journal Ecography, confirms what has long been suspected: that in the daytime koalas choose bigger trees with thicker foliage for the purposes of thermoregulation.
“If it is really hot they have to go to trees down in gullies, and often they want to go into bigger trees during the day, and trees which have a lot more shelter that keep them protected from the heat,” Dr Crowther said.
Without shelter, koalas dying in heat
Dr Crowther says that in the patchy rural landscape of the rich Liverpool Plains near Gunnedah, koala survival may depend on those larger, mature trees.
“The problem is when you get a week of days over 40 degrees, which does happen in Gunnedah, you tend to get koalas dying,” he said.
“They can’t get shelter from the heat, they can’t maintain their water requirements, and you will find koalas dead and dying at the base of trees.”
They can’t get shelter from the heat, they can’t maintain their water requirements, and you will find koalas dead and dying at the base of trees.
Dr Matthew Crowther
Dr Crowther says the findings are significant for ensuring the survival of koala populations right up into Queensland, and show the importance of continuing research into even those animals that are thought to be well understood.
The tree-use study could mean that habitat restoration, or biobanking proposals based on planting food trees, are doomed to fail unless mature older trees required for shelter are also maintained.
The finding could be highly significant for Gunnedah, which the local council calls the “koala capital of the world”, and where a number of major mining projects are under consideration.
The environmental statement for one open-cut coal mine proposal, the Shenhua Watermark mine 25 kilometres south-east of Gunnedah, is proposing a habitat-replacement deal.
The environmental impact statement for the project says koala habitat must be removed because coal lies beneath.
By Nonee Walsh | First posted Thu 3 Oct 2013, 8:16am AEST | Updated Thu 3 Oct 2013, 8:30am AEST