The case of the zombie roadkill

Bullsh*t, I swore gently under my breath. There’s just no way.

That’s how one of the most interesting discoveries of my PhD began. A little bit of coarse language and a healthy dose of skepticism.

I’d just received an email. Apparently an ecologist, in the course of their daily round of noticing things that normal people don’t notice, found a dead squirrel glider on the side of the Hume Freeway. It was sporting a fancy radio-collar. They wondered if the animal might be ours.

Impossible. Our most recent radio-tracking study had finished months ago. But if they had the details of the animal, I’d check anyway. Collar number. Tattoo number. Gender. Everything matched. That’s when I swore.

I swore because the unfortunate glider was from Longwood, in northeast Victoria. I swore because it was found dead on a roadside just outside of Goulburn, New South Wales. I swore because I was morbidly excited.

To be clear, I don’t enjoy dead animals. But this particular dead animal – let’s call him Bob – was kind of interesting. How had he found himself dead on the highway 500 km away from his home? (spoiler alert: Bob was not a zombie).

First, we had to be absolutely sure that this was, in fact, Bob from Longwood. To get solid proof, we needed his microchip number. Each microchip has a unique 10-digit code so we can accurately tell our animals apart. But it needs to be read with a special scanner. So, Deryk, the ever helpful ecologist who recovered poor Bob from the roadside, stored the tiny furry body in his freezer at home until we could scan it. Aside from a minor incident where Bob was nearly defrosted alongside some Porterhouse steaks, he kept well. Low and behold, when I finally visited a year later, that magic little number matched exactly.

Now we needed to do a little detective work to piece together the story. We’ll never know exactly what happened to Bob that fateful night, but here’s what we did know.

Bob probably wasn’t killed at Longwood. He disappeared a few months into our study and though we searched long and hard, we never saw him again. But his body was found fresh on the roadside 12 months later. So in the mean time, he’d obviously shifted to live some place new, outside of the range of pesky researchers and their radio-tracking equipment.

Bob definitely didn’t make the 500 km journey to Goulburn on his own. The squirrel gliders we tracked sometimes moved up to 2 km a night – quite a distance for an animal weighing in at only 250g. But 2 km is a far cry from 500 km. Even if gliders could trek such long distances, the landscape between Victoria and New South Wales is so fragmented that there would be simply too many barriers along the way.

The most likely scenario? Young Bob was on the move. He left our study area, possibly in search of a little patch to call his own. Some time later he had to cross the highway somewhere dangerous, and got very unlucky. Then, wedged onto the vehicle that struck him, Bob travelled the Hume until he was unceremoniously dislodged a few clicks south of Goulburn (home of the big Merino FYI).

Why is this interesting? Well, we’ve always known that counting roadkill for small animals was difficult. Squirrel gliders are small and, rather inconveniently, exactly the same colour as the pavement. This means they’re tricky to spot. Now that we know they can end up 100s of km from the place they’re hit, roadkill counts are looking like an even less reliable measure for this species. And it turns out that this isn’t unique to squirrel gliders. Animals as big as koalas have been found wedged under the bumpers of cars or trucks. So when it comes to understanding the impacts of roads, or selecting places where crossing structures should go, it seems that a carcass on the roadside only tells part of the story. But we road ecologists are always working to learn more – I swear.