Threatened Sheep With GPS Backpacks Are Only Out For Themselves

July 23, 2012 § Leave a comment

Stick a dog in a pasture full of sheep, you’re going to have yourself a full-on every-ovine-for-itself stampede to the center of the herd—because each and every sheep on that field wants to make sure his edible neighbor gets eaten first. There will be no heroics, and at long last, say researchers from the University of London, they’ve got the numbers to prove it.

The study, which appears online today in Current Biology, set out to quantify what’s known as the Selfish Herd hypothesis: animals that stick together do so to reduce their individual odds of being killed (Ha ha! Won’t eat me if it gets Bob first!). Sheep do it, in theory, as do crabs, seals, insects, fish, and just about every other animal that typically flocks. In this case, the researchers took 46 sheep, one Australian Kelpie working dog, and 47 GPS trackers—one per animal—then set the dog to work herding sheep through a gate in three trials over three different days. In each case, according to the second-by-second data collected from the devices, as soon as the dog came within roughly 70 meters of the group, the sheep clustered together, forming a tight herd in their haste to get not just next to their fellow sheep, but into the dead center of the group, which itself collectively and simultaneously shifted away from the threat.

Wait, what’s that you say? You’re not shocked? This was common knowledge? Correct, says Andrew King, lead author of the study. In fact, the idea’s been around since at least 1971. “It’s one of those things that everyone kind of agrees happens, but it’s really tough to measure.” For one thing, predators don’t attack on cue, and the technology used, up to now, has had to be painfully roundabout: video cameras, photographs, computer simulations.

See, the real breakthrough here isn’t the sheep, or even the confirmation of the theory. No, the real finding is the functional demonstration of those durable, compact, 150-gram GPS devices. They’ve been under development for years by the second author of the study, Alan Wilson, a longtime authority when it comes to finding new ways to assess and track animal motion, and have really just the stage where they can be produced en masse to track the second-by-second, long-term movement of literally entire herds of animals. “The technology’s really just opened up new doors and we can begin to look in finer detail in space and time and get more data,” King says. “We can start working with mathematicians and physicists to say, ‘Okay, this is how the sheep are moving, so what group behavior rules are they following?’ That’s the fun bit that comes next.”

Because really, knowing the rules is the key to the science. It’s the only way that researchers can really assess when they’re being broken—as in say, the gradual development of disordered movement and social interaction in the Huntington’s Disease sheep model. Or the prion disease model. The Tay-sachs sheep model. Or you can look across species to see where else the same behaviors pick up. Remarkably often, different species in different contexts seem to be operating under very similar rules. “It’s suggesting kind of fundamental, shared principles across these animal groups,” King says. He’s already done extensive work mapping out baboon behavior; now, he’s headed to Botswana to track the social life of the cheetah.

Reference & Photo Credit: King A, Wilson AM, Wilshin SD, et al. Selfish-herd behaviour of sheep under threat. Current Biology, 2012, 22:R561. (doi:10.1016/j.cub.2012.05.008). 


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