Credit: Laurence Connor
Credit: Laurence Connor

Lion-Trackers Get Sight Beyond Sight with Laser-Plane

Imagine getting a lion’s eye view of a hunt, and seeing every shrub, tree or rock that it sees. You can practically feel the creature’s see-sawing shoulder-blades and stealthy footfalls as it stalks through the undergrowth towards an unwary impala.

How would you do this? The obvious way would be to traipse about the savannah after a lion, but bear in mind that these predators typically hunt at night, and often among thick vegetation.  “That’s a place most ecologists won’t go, at least not anyone in their right mind,” says Greg Asner from the Carnegie Institution for Science. “It is very spooky.”

Asner had a different approach. To see what the lions see from the ground, he took to the skies.

While most ecologists trundle through the field, Asner can usually be found soaring overheard in a plane armed with a trinity of the most sophisticated sensors around. Collectively, they’re known as AToMS—the Airborne Taxonomic Mapping System. Two of them can measure the various wavelengths of light that reflect off underlying vegetation, and use these signals to reconstruct the plants’ chemical composition in real-time.

The third—a grey box called LiDAR—sends two lasers scissoring across the ground at 400,000 pulses per second and uses the echoes to map the shape of every branch and twig. As he flies overhead, Asner can create gorgeous, three-dimensional maps of the land below, at speeds of more than 100 kilometres per hour. He has flown over the rainforests of Peru, Colombia, Ecuador and more. [See my long feature on Asner’s work.]

But since 2008, he has also been laser-scanning South Africa’s Kruger National Park to understand how the animals there interact with the plants. He’s mapped how often elephants knock down trees and how termite mounds reflect changing climate. Now, he has turned his attention to lions.

Between 2005 and 2007, Craig Tambling from the University of Pretoria fitted seven lions—five females and two males—with GPS collars, and tracked their whereabouts to find where they killed their prey. When lions kill, they effectively cough up a big hairball of fur, bones, horns and teeth. And even though they’ll often drag a carcass for long distances, they usually hack up their guts within a few metres of the kill spot. By following the GPS signals and looking out for these stomach contents, Tambling could mark every spot where his lions had taken down some prey.

In the spring of 2008, Asner, together with teammate Scott Laurie, mapped the same areas that Tambling had surveyed. The team marked each kill site on their three-dimensional maps and plotted lines of sight in every direction. That gave them a pretty decent picture of what each lion would have seen, had it looked up just before coughing up its hairball. (Obviously, with a timelag of one to three years, the view wouldn’t have been an exact replica, but the general structure of the Kruger’s vegetation tends to stay the same within that timescale.)

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From Loarie et al, 2013. Animal Behaviour

These, er, lions-of-sight showed that males and females hunt in different types of terrain. On average, the females dispatch their prey at places where they can see for 8.6 metres around them. Males, however, kill at sites with thicker cover, where they can only see for 3.4 metres around. So while females cooperate to chase prey across open terrain, males are more likely to be ambush-hunters, launching attacks from long grass or dense shrubs.

These results help to explain why male and female lions are equally matched killers. Males were traditionally thought to be less successful than females, but recent studies put both sexes on a par with each other. But why? How do males succeed as solo operators when the females can rely on teamwork?

In 2001, Paul Funston, a lion specialist at the Tshwane University of Technology, reported one possible reason: They attack different prey. The females tend to take medium-sized animals like zebra and wildebeest, while the more powerful males tackle big game like buffalo. Funston also found hints that the males are better at catching smaller prey like impala when they hunt among thicker vegetation—something that Asner’s fly-over study has now confirmed.

Asner fully admits that his team only looked at a small number of lions from a narrow corner of the Kruger National Park. “We recommend that these results be viewed more as a case study to motivate larger-scale studies rather than as a broad generalization of lion hunting behaviour,” he wrote.

Still, the results make sense to Matt Hayward of the Australian Wildlife Conservancy, who has spent time in Africa and studied the hunting habits of lions. “Anyone who has watched male lions hunt can see how much of a hindrance their mane is for stalking, particularly in open areas. They need more cover,” he says. “Females, however, can put their heads back, flatten their ears and look down their noses to present a flat, well camouflaged profile for stalking prey.”

These results have immediate relevance for the people running South Africa’s National Park Service. Rangers use fire to actively manage the amount of woody vegetation in the park—vegetation that’s crucial for supporting the full range of interactions between lions and their prey. “The male lion behaviours are keyed to it,” Asner says.

Beyond that, the study is another vindication for Asner’s high-flying approach to ecology. He has achieved sight beyond sight—a surprisingly grounded view of the lions’ world, taken from a paradoxically lofty perspective. “This is the future of ecology and conservation,” he says.

“The story here may be about removing the biologist from the observation of animal behaviour which, although cool, techy and geeky, is sad at some level,” says Funston. “I found the same basic findings through months and months of dedicated field work, and always chuckled a bit at Craig Tambling sitting in his tent waiting for the data from GPS collars to come to him. Nevertheless, we have to progress and here we have a novel application of two technologies to an interesting scientific question.”

Reference: Loarie, Tambling & Asner. 2013. Lion hunting behaviour and vegetation structure in an African savanna.

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