The bar-headed goose (Anser indicus) flies over the tallest peaks of the Himalayas as it migrates from India to Mongolia each year. When oxygen levels in the thin air dip as low as 7 percent, the bird’s metabolism likewise dips to accommodate, yet its wings beat just as fast as before, researchers reported August 3 in eLife.
The goose’s high-altitude flights have been a biological mystery for decades. A mountain climber spotted a bar-headed goose overhead while summiting Mount Everest back in 1953, according to Science. Scientists marveled at how the creature could ascend nine kilometers above the earth?—two kilometers higher than any other known animal flies.
Scientists have long known that bar-headed geese boast an enhanced ability to bind oxygen to their hemoglobin. A study conducted in 2009 also revealed that the birds sport more capillaries around their pectoral muscle cells than related species that don’t soar to such heights. Various researchers have also studied the birds at rest and while walking on a treadmill in normal and hypoxic conditions, but haven’t addressed how the birds handle low-oxygen levels in flight.
To fill this gap in the literature, physiologist and NASA astronaut Jessica Meir and her colleagues devised a unique experiment: starting in 2010, the team raised 19 geese from hatchlings and trained them to fly in a 30-yard-long wind tunnel while fitted with physiological sensors and oxygen masks, according to The Washington Post. The masks simulated low-, medium-, and high-altitude air conditions while the sensors clocked the birds’ heart rate, blood oxygen levels, temperature, and metabolic rate.
To train their birds from birth, the team took advantage of the fact that hatchlings bond with the first large shape they see, a behavior known as “imprinting.” A dozen of the goslings, whose eggs were collected from Sylvan Heights Bird Park in Scotland Neck, North Carolina, imprinted on Meir and spent countless hours with her, nuzzling with her and learning to fly outdoors, and in the wind tunnel, according to the Post.
“It was one of the most amazing things I’ve ever experienced in my life,” says Meir in an interview with the Post. Before flying in the wind tunnel, the goslings would fly alongside Meir while she rode her bike, and, later, her motor scooter. “It would be flying so close to me that its wing tip would be sometimes brushing my arm. I am looking right into the eye of this flying bird, not to mention my baby,” Meir says.
In the wind tunnel experiments, the researchers found that the adult geese slowed their metabolism and heart rate in low-oxygen conditions and somehow cooled their blood. Hemoglobin binds oxygen more tightly in cooler conditions, meaning the birds’ blood carried more oxygen while the animals simultaneously burned fewer calories, according to the Post. The geese also adopted more-efficient flight strategies by altering the biomechanics of their wingbeats, according to The New York Times.
“The bar-heads have done that migration for millions of years before the Himalayas were as tall as they are now, and the birds have been pushed as the mountains have moved up to go higher and higher,” says coauthor Julia York, now a graduate student at the University of Texas at Austin, in an interview with the Times. York, who played foster parent to seven geese, adds, “They’re amazing athletes.”
The findings should lay the groundwork for future investigations of high-altitude physiology and they potentially have relevance to human medicine, where heart attacks, strokes, and organ transplants subject patients to low-oxygen conditions, says Meir in a press release. Meir will soon soar even higher than her geese, blasting off to the International Space Station on September 25. There, she will help study how lengthy space flights affect human physiology and serve as a study participant herself.
“I’m finally paying my dues,” she tells the Post. “I’m going to be the one poked and prodded.”
Nicoletta Lanese is an intern at The Scientist. Email her at firstname.lastname@example.org.