It’s cool and fun for a goose to be a goose because it has the enviable ability of migrating from one end of the world to the other enjoying great weather and a natural view of awesome creations not available to air-flight passengers – but beyond this, geese navigate mountains by roller-coastering at low altitude, allowing them to flying over thousands of mountainous regions and not get tired from the long seasonal flights.
Specifically, the bar-headed geese migrate each autumn south of their breeding grounds in Mongolia to Southeastern Tibet or India. And desiring to crack the code behind their abilities to fly for so long each season without fagging out, scientists implanted 30 geese with a device that records body movement, heart rate, and flown altitude. They recaptured 17 of them after the seasonal flight but were only able to utilize data from seven of them – and what they found challenged long-held ideas about the geese’s migratory tricks.
“At the beginning we were just puzzled that there were so few reports of very high flight over the last 60 years,” Charles Bishop, the University of Bangor researcher who led the study, says. “We knew that these birds were especially well-adapted to fly in air containing very low oxygen, so we certainly expected to record some high flights. The question was, how high did they normally fly? For how long? And how difficult were such flights? How close to the limit did they have to go?”
Scientists have long held the idea that bar-headed geese spent their migratory hours at high altitudes where their flight is aided by favorable tailwind, but Bishop’s team found that these birds actually traverse the Himalayas by hugging the mountainous terrain. They fly closer to the ground as the mountain undulates in a way that makes them enjoy a roller coaster flight.
And the reason for this flight strategy is simple: flying 1,000 miles at 20,000 feet high in the air is hard work because oxygen is scarcer at very high altitudes and the endeavor is much tiring to the birds. So the bar-headed geese fly lower closer to the mountains where abundant oxygen translates to an economical flight.
“I think it is the most economical way to travel through the mountains,” Bishop said. “It might be justified for a bird to choose to fly a bit higher if there was a tailwind helping it cover the ground quicker. In this way it would reduce the travel time as well as reduce the overall energy cost for the journey. However, it appears that the winds were seldom blowing in the right direction to help the geese with their migrations, so the best thing to do is stay as low as possible and keep in the most dense air available.”
And Bishop adds that dropping to lower altitudes is nothing for the geese because it is only exploiting gravity and its effects on its flight. “If a wind hits a mountain ridge in the ground or a large wave at sea, then some of it will be deflected upwards and create an updraft,” Bishop said. “A bird can use this to help it when climbing – it increases [the bird’s] rate of climb, reduces the energy required to climb at some rate, or a bit of both. When flying horizontally, it decreases the energy that needs to be supplied to the air to fly along.”
He goes on to add that “It is a spectacular migration through 500 kilometers of the highest mountain area in the world. These birds do not appear to need to train before going on long migratory flights, nor do they need to acclimatize. Presumably, they not only get fit ‘naturally,’ but they also do not suffer from mountain sickness.
“They could walk at the top of Everest with no difficulty and no ill effects,” Bishop said. “It would be fantastic if we could do this. The only Olympic Games held at any significant altitude was that of Mexico City at only 2200 meters. At these games, men broke all world records below 800 meters – but at 1500 meters they slowed down, and the 3000 meter steeplechase upwards performances were 6% slower than world record time. These birds would probably not have noticed a thing.”
With this research published in the journal Science, the final note here is that humans could deploy the biomechanical strategies behind the bar-headed geese’s flight in the future for some commercial endeavors; and they could just agree that being a goose is fun and cool.
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