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Burrowing echidnas essential for health of Australian environment

Echidnas are Australian soil-moving champions

The Company of Biologists

Australia may not immediately spring to mind as your archetypal Noah's ark, but the list of native creatures that make their homes on the vast continent reads like an encyclopaedia of species from Gondwanaland, ranging from monotremes to marsupials. Of the five surviving monotremes, platypuses and short-beaked echidnas are the only two that make their homes in Australia and although little is known about the life styles of either one, Christine Cooper, from Curtin University, Australia, and Phil Withers, from the nearby University of Western Australia, are beginning to uncover details about the echidna's physiology. So when Cooper and Withers invited Christofer Clemente, from the University of the Sunshine Coast, Australia, to hop on the back of their echidna fieldwork to learn more about the animals' day-to-day antics, Clemente jumped at the offer. The team publish their discovery that individual echidnas are responsible for aerating 200m3 of soil each year, making them a keystone species in the ecological health of the continent, in Journal of Experimental Biology at http://jeb.biologists.org.

'I had these little accelerometers that I had got from the University of Queensland', says Clemente, who admits that when Cooper and Withers suggested teaming up he was having a frustrating time attaching them to the backs of lizards that promptly vanished into the bush. Would the echidnas prove more cooperative? Within a few weeks, he found himself driving with Cooper and Withers to the Dryandra Woodland to track the spikey monotremes, and this time his patience was rewarded. Despite searing daytime temperatures of 45°C and the echidnas hunkering down for lengthy periods in caves, the team was able to retrieve the trackers successfully. 'And when I went back and looked at the data, it was fantastic', laughs Clemente. The only drawback was the tracker's short (24 h) battery life, so Clemente collaborated with University of Queensland engineers Surya Singh and Philip Terrill to redesign them. 'The [new] sensors were very small, about the size of a postage stamp', says Clemente, recalling how Craig Freakley individually hand-soldered each component onto the new chips using a microscope and minute soldering iron. Returning with the redesigned trackers to Dryandra 18 months later in the spring with Cooper, Withers and Freakley, Clemente filmed the echidnas so that they could correlate the accelerometer traces with specific echidna behaviours to get a handle on the private lives of the elusive animals.

Recalling that the temperature difference between the summer and spring was about 25°C, Clemente says, 'I was interested in how echidna activity changes with these differences and we found that there is a huge effect'. During spring, the animals waddled around at a stately 0.3m/s for much of the day. However, when the temperatures rocketed, the animals dramatically reduced their activity to a couple of hours in the morning and, instead of walking, they sprinted everywhere at their top speed of around 0.6m/s; 'They certainly try to avoid really hot temperatures', says Clemente.

During the first field trip, he had also noticed a large number of digging scars in the ground where the animals had been prospecting for their favourite snacks - juicy termites. Wondering how much of an impact the animals' excavations might have on the environment, Clemente was impressed to see that they invested as much as 10% of each day in digging. And when he calculated how much soil an individual could shift in a year, it was an impressive 200m3; 'so if you have 12 echidnas, they are moving the volume of an Olympic-sized swimming pool of dirt a year, which is quite a lot', laughs Clemente. And he suspects that the echidna's monumental earthworks could have profound implications for Australia's environmental health. Explaining that the echidna is one of the few native burrowing species surviving in Australia and that burrowing animals are essential for aerating soil and mixing in organic material, Clemente says, 'They are probably one of the last really big bioturbators [soil mixers] left in Australia, which means that they are really important for the environment'.

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IF REPORTING THIS STORY, PLEASE MENTION JOURNAL OF EXPERIMENTAL BIOLOGY AS THE SOURCE AND, IF REPORTING ONLINE, PLEASE CARRY A LINK TO: http://jeb.biologists.org/content/219/20/3271.abstract

REFERENCE: Clemente, C. J., Cooper, C. E., Withers, P. C., Freakley, C., Singh S. and Terrill, P. (2016). The private life of echidnas: using accelerometry and GPS to examine field biomechanics and assess the ecological impact of a widespread, semi-fossorial monotreme. J. Exp. Biol. 219, 3271-3283.

DOI: 10.1242/jeb.143867

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