Rosy-faced lovebirds have jacked necks for climbing

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Tartufo, the pink-faced lovebird, has more limbs than you think. He has two wings, which of course he uses to fly. It has two legs that it uses to grab branches and hop around the canopy. But when it comes to a particularly steep tree, he relies on a third party: his head.

Pink-faced lovebirds – a type of tiny parrot – are among a few vertebrates that walk with an odd number of limbs, based on climbing experiments published this month in the journal Proceedings of the Royal Society Biological Sciences.

Many animals have what the study’s lead author, Michael Granatosky, calls “effective limbs,” like a tail that acts as a tripod. But fewer actually use a spare limb to propel or pull themselves forward. “Now we’re talking about things that are much rarer in evolutionary history,” says Granatosky, who studies the evolution of locomotion at the New York Institute of Technology. Kangaroos use their tails like a feather to jump, and spider monkeys use a nimble tail to climb through trees. “But “for the first time with these parrots, [we’ve found] an animal that uses its head as a driving link”

To find out how parrots use their heads, the team set up a “landing strip” that contained a small pressure sensor that recorded push and pull movements. This enabled them to distinguish when a bird was just hanging by its mouth for its life and when it was actually dragging itself along. The six rosy lovebirds in the experiment were all able to do neck pull-ups for climbing.

Granatosky has a pet cockatiel, Rex, says Melody Young, the paper’s lead author and a graduate student at the New York Institute of Technology. “So he was watching his parrot climbing and he was like, ‘I want those powers.'”

But larger parrots, like macaws, are tougher subjects to study because they bite hard enough to rip off a finger when crabby. So the team turned to rosy lovebirds as models instead because they’re good-natured. If anything, Young says, “they’re too friendly.”

If anything, “they’re too friendly,” says co-writer Melody Young of the rosy lovebirds. Steven Gaines, New York Institute of Technology College of Osteopathic Medicine

“They climbed you the same way they climbed the runway,” adds Granatosky. “The hardest part is keeping them there.”

But the lovebirds are not defenseless. In order to head climb, its neck must be about four times stronger per body weight than ours and deliver bites with a force equal to fourteen times its body weight. “If they get lively and we’re not wearing gloves,” says Granatosky, “they can draw some blood.”

The parrots do not always walk with three limbs. By tilting the runway, the researchers showed that they didn’t use their mouths until they were walking up a 45-degree incline, and increasingly relied on their heads as the runway got steeper.

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For the lovebirds, the head is therefore a close analogue of how humans use our arms when climbing. Young is currently planning a series of human experiments using stepping walls — a short section of a climbing wall that moves like a treadmill — to understand how both novice and experienced climbers actually move up a wall. The experiments are a starting point to explore treatments for people who need to develop shoulder and leg strength and to envision new ways of building climbing robots.

The sheer oddness of using a head to move suggests something mysterious in the parrot’s brain. When animals move, their brains produce repetitive patterns to control the sequence of steps — “that’s why you don’t have to think about walking, right?” says Granatosky. Unlike other birds that jump trees, “parrots move just like us. Everything is left, right, alternating movements.” Being able to fit a third, asymmetrical limb movement into this sequence is “odd from an evolutionary perspective,” he says.

Since the article was published, Granatosky says, people have come forward with their own stories of three-legged moves — or even head-assisted tree climbing. “The weirdest email was about hunting dogs,” he says. “Dogs that are trained to put animals up trees, a small percentage of them learn to climb the tree with their heads.” Strange as head-driven climbing may seem, it may be more common than evolutionary biologists currently believe.