Slowed metabolism helps migrating geese soar

The team collected the first ever cardiorespiratory measurements of bar-headed geese flying in a wind tunnel at a simulated altitude of 9,000m. They discovered that the animals are able to maintain flight in these low-oxygen conditions via a reduction in their metabolism.

Bar-headed geese are famed for migratory flight at extreme altitudes, having been directly tracked flying as high as 7,290m, and anecdotally reported reaching 9,000m. Previous research suggests these birds have several adaptations that allow them to maximise their oxygen usage at high altitudes, such as the ability to deliver oxygen efficiently to individual cells. But until now, no studies have comprehensively measured the physiology of bar-headed geese during flight in low-oxygen conditions, partly because there are few wind tunnels in the world suitable to carry out such experiments.

To address this gap in our knowledge, a research team from the University of British Columbia (UBC), Vancouver, Canada, imprinted a flock of bar-headed geese born and raised at sea-level, and trained them to fly in a wind tunnel. The group was led by Jessica Meir, a postdoctoral researcher in Bill Milsom's lab at UBC at the time the study was carried out, along with Julia York, an undergraduate researcher, currently a PhD candidate at the University of Texas at Austin, US.

They found that six of the seven birds that could fly in the tunnel were capable of flight in moderately low-oxygen levels equal to around 5,500m -- the altitudes at which their wild counterparts typically fly. Three of the birds were also willing to fly in severely low-oxygen conditions, equal to altitudes of roughly 9,000m, for at least the short duration of the flights carried out in the study.

"We were surprised to find their heart rate during flights in reduced oxygen was no higher than that during flights in normal oxygen levels," York says. "We also saw that the temperature in their veins decreased during our simulated flights, which is hypothesised to significantly increase the amount of oxygen they can carry in their blood. Our data suggest the animals are able to reduce their metabolism in line with the reduced amount of oxygen available, without evidence of an oxygen limitation."

Milsom adds that determining how these results relate to the longer migratory flights of bar-headed geese at high altitudes will require further work to measure the physiological variables in the wild, or during longer flights in both normal and low-oxygen conditions.

"These initial measurements pave the way for future experiments that we believe will significantly move the field of high-altitude physiology forward," Meir explains. "Additionally, our findings have relevance to all physiological and biomedical fields involving animals and humans in low-oxygen environments, such as medical conditions including heart attacks and strokes, or procedures like organ transplants."

This study is one of a number of experiments carried out by Meir during her research career to see how animals cope in extreme conditions. Her previous work has involved travelling to Antarctica to study the adaptations of emperor penguins to long underwater dives.

Meir is currently a NASA astronaut, scheduled to launch to the International Space Station for a six-month mission on September 25, 2019, where she will support research into a diversity of space sciences including how long-duration spaceflight affects human physiology.