For humans, climbing Mount Everest is seen as a great feat. People make movies, write books, and have essentially developed a whole industry surrounding the challenge that is this mountain.
While we consider climbing the mountain as an athletic achievement, there is one animal that does not: the bar-headed goose.
As the species migrate from Central Asia to Southeast Asia every autumn, it must cross over the Himalayan mountain range. These mountains force the bar-headed goose to fly at around 30,000 feet above sea level, making it the highest altitude migration of all birds on earth.
A Story Of Adaptation
The bar-headed goose’s ability to fly over the Himalayas is no easy feat. Many would think that lack of oxygen and air for support would force the birds to migrate through mountain passes at lower altitudes, as other birds do.
However, these geese have special adaptations that allow them to survive at an altitude at which few other animals can. For example, a mutation in their hemoglobin (a protein in blood cells that transports oxygen throughout the body) allows their blood cells to be more efficient at binding to oxygen.
Their circulatory system provides a constant supply of fresh, oxygenated blood to their wing muscles. They have much larger lungs than other birds, giving them the ability to take in more air. These various biological adaptations give the geese a great advantage when it comes to working efficiently at high altitudes.
The Flight Of The Goose
In 2011, scientists from Bangor University began a study to learn about the flight of the bar-headed geese. They tagged and implanted 30 geese with sensors to measure altitude, heart rate, and movement.
Although they were only able to collect final data from seven of those geese, the results were surprising. They had initially believed that the geese flew at an extremely high altitude for the full length of their migration (around 1,000 miles). But data suggests that the birds use a much more efficient way of travel: roller coaster style.
Rather than remaining at an extremely high altitude to fly over the mountain range, the geese hug the mountains, flying up and down depending on the obstacles in their way. This works better for them because they don’t have to expend all their energy flying in a region with low oxygen; they can spend time flying at lower altitudes.
You may be wondering: aren’t they doing more work by constantly flying down and over the mountains? The geese make use of natural phenomena to make this work easier. To fly down, they simply allow gravity to pull them. To fly back up, they make use of an orographic lift, which happens when flowing air meets an obstacle, such as a mountain. The mountain forces the air up, essentially creating an upward draft. The birds take advantage of this draft, expending less of their own energy to fly up the mountain.
The way these birds have adapted to flying across the Asian continent during their annual migration is certainly an amazing way to see nature at work.