The Bizarre, High-Tech Art Of Tracking Toads

Cane toads are a major pest in Australia. In an effort to contain them, researchers are tracking the beasts and trying to understand where they'll go next. But how do you track a toad? Two words: Accelerometer and pantyhose.

As any Australian will tell you, cane toads (Bufo marinus) are an introduced pest which have resisted every attempt at control. Part of the problem it's that it's hard to control a creature you don't understand, and nobody really knows what cane toads' metabolic rates and energy expenditures are. Those are two bits of information that help biologists predict where an animal population will expand.

So how do you go about measuring the energy expenditure of a bunch of wild animals? The most common techniques are the doubly-labeled water technique, which tracks key molecules as they travel through an animal's digestive system, and the heart rate technique, which measures heart rate. The problem is that these techniques don't work for amphibians.

The scientists at Roehampton University, London and The University of Queensland had to blaze a new path. They used an accelerometer - just like the one in your smart phone. If you can measure the body motion of an animal, taking into account its oxygen consumption, you get what's known as the 'overall dynamic body acceleration' or ODBA. And the ODBA is enough for scientists to figure out cane toad energy expenditures.

The Bizarre, High-Tech Art Of Tracking Toads

Getting an accelerometer onto the back of a toad isn't exactly an easy task, so researchers relied on humanity's greatest invention: pantyhose. Write the researchers:

Firstly, a section of pantyhose material (YLC, containing nylon, elastane and cotton), with the toe end cut off and the remaining garment wrapped back on itself to create a loop, was placed around the body of the toad. A firm fit on the toad was achieved by placing the material around the toad between the front and back legs, then twisting the material on the back of the toad to make a second, upper loop, and finally pulling the upper loop down over the head of the toad to fit behind the head and anterior to the front legs. This created an x-shaped cross of material on the back of the animal under which the logger could be firmly placed without restricting the movement of the animal's legs and, since the material allows diffusion of air, without restricting cutaneous gas exchange. Further, the material remained fitted to the body of the animal regardless of whether the toad expanded its lungs or not. The logger was placed broadside against the skin with the length along the antero-posterior axis and the battery attached dorsally to the logger.

I dearly, dearly wish pictures of this had been included in the article.

This study was as much a proof of concept as anything, and it proved that this method was practical for analyzing cold-blooded animals. It sheds light on two different important metrics — how the animals move, and their energy requirements. The toads moved on average about 4% of the time, at around 18 meters per hour, and the results showed that the metabolic rate of the toads in the wild may be considerably higher than previously thought. That means they require more food than scientists had realized. And they'll be spreading faster, as they look for it.

[full publication available at PLoS]