The truffle, a purple bird with a pink face, has more limbs than you think. It has two wings which, of course, it uses for flight. He has two legs, which he uses to grab branches and jump on the canopy. But when confronted with a particularly steep tree, he relies on a third: his head.
Based on climbing experiments published this month in a journal Proceedings of the Royal Society of Biological Sciencespink-faced pigeons - a species of small parrot - are members of rare vertebrates that walk with an odd number of limbs.
Many animals have what the study’s older author, Michael Granatoski, calls “efficient limbs,” like a tripod-like tail. But fewer of them actually use the spare limb to push or pull. “Now we’re talking about things that are much rarer in the history of evolution,” said Granatoski, who studies the evolution of the movement at the Institute of Technology in New York. Kangaroos use their tails as a source for jumping, and spider monkeys climb through trees with deft tails. “But” for the first time with these parrots, [we’ve found] an animal that uses its head as a propulsive limb “
To decide how the parrots use their heads, the team set up a “runway” with a small pressure sensor that detected pushing and pulling movements. This allowed them to discern when the bird was just hanging by the mouth, or when it was actually dragging behind. The six pink-faced birds in love in the experiment were all able to raise their necks to climb.
Granatoski has a pet, Rex, says Melody Young, the paper’s lead author and a graduate student at the New York Institute of Technology. “Well, he’d watch his parrot climb up and think, ‘I want those strength.’
But larger parrots, like macaws, are heavier objects to study because they bite hard enough to take their finger off if they are grumpy. Instead, the team turned to lovebirds with pink faces as a model because they are sweet tempers. If nothing else, Young says, “they are too friendly.
“They would climb you as much as they would climb the runway,” Granatoski added. “The hardest part is trying to keep them there.”
But lovebirds are not helpless. In order to climb with their heads, their necks must be about four times stronger in body weight than ours, and bite with a force that is fourteen times greater than their body weight. “If they get fierce and we don’t wear gloves,” Granatoski says, “I can draw some blood.”
Parrots do not always walk with three limbs. By tilting the runway, the researchers showed that they started using their mouths only when they climbed at a slope of 45 degrees, and that they relied more and more on their heads as the runway became steeper.
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For birds in love, this makes the head a close analogue of the way people use our hands when climbing rocks. Right now, Young is planning a series of experiments on people involving running walls - a short section of climbing wall that moves like a treadmill - to understand how both beginners and professional climbers actually move along a wall. Experiments are the starting point for studying treatments for people who need to develop shoulder and leg strength and imagine new ways to build a climbing robot.
The sheer unusualness of using the 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, do you?” Says Granatoski. Parrots, unlike other birds that jump on trees, move like us. Everything is left, right, alternating movements. ” The possibility of including a third, asymmetrical limb movement in that sequence is “strange from an evolutionary perspective,” he says.
Since publishing the newspaper, Granatoski says people have resorted to their own stories of moving on a tripod - or even climbing trees with their heads. “The strangest e-mail was about hunting dogs,” he says. “Dogs that are trained to put animals on trees, a small percentage of them learn to use their head to climb a tree. As strange as climbing on one’s head may seem, it could be more common than evolutionary biologists currently realize.