There are over 10,000 bird species in the world. Most of these birds (but not all) are capable of flight. And, most choose to fly at relatively low altitudes. Your average house sparrow, for instance, rarely ventures more than a few hundred feet in the air.

But there are some birds that push the limits of upward flight. Perhaps the most iconic example is Africa’s Ruppell’s griffon, for which there is confirmed evidence of it reaching flying altitudes of 35,000+ feet – earning it the title of world’s “highest flying bird.”

Another equally interesting example of a high-flying bird is the bar-headed goose. The bar-headed goose is one of the only birds on Earth capable of crossing the Himalayan mountain chain. In fact, not only is it capable of crossing the Himalayas, it does so on an annual basis, choosing to spend its winters on the Indian subcontinent and its summers on the central Asian steppe.

As if it likes the challenge, the bar-headed goose doesn’t even bother to take a lower elevation route through the Himalayas. There are documented sightings of the bird above Mount Makalu (the fifth highest mountain on Earth, at an elevation of 27,825 feet) and there is speculation that the goose has even circumnavigated Mount Everest.

Here’s more detail on the one-of-a-kind bar-headed goose and its incredible migratory pattern.

(: While the Ruppell’s griffon and bar-headed goose are among the best-known high-altitude flyers – meet 5 other birds that routinely take to the skies at extreme elevations.)

The bar-headed goose (Anser indicus) is a marvel of avian physiology. Named for the distinctive dark stripes running across the back of its head, this medium-sized goose is specially adapted for one of the most extreme migrations in the animal kingdom. Every year, thousands of bar-headed geese fly from the wetlands of India and Bangladesh to their summer breeding grounds in Mongolia and China – a journey that takes them over the highest peaks of the Himalayas.

What makes this journey so extraordinary is not just the height the birds reach, but the conditions they endure while doing so. At altitudes above 20,000 feet, the air is perilously thin, with oxygen levels about a third of what they are at sea level. Temperatures plummet well below freezing, and fierce winds rip across the high passes. Yet the bar-headed goose sails through these extremes with little resistance.

How do they do it? Research into the bar-headed goose’s physiology has revealed a number of adaptations. Their lungs and chest muscles are more efficient than those of other birds, allowing them to extract more oxygen from the thin air. Their blood contains a unique form of hemoglobin that binds oxygen more tightly, ensuring that their muscles receive sufficient fuel even in oxygen-deprived environments.

In addition, the geese excel at managing their energy. They tend to fly at night or in the early morning when the air is cooler and denser, which makes flying slightly easier. While the birds can’t take advantage of daytime upslope tailwinds, which could reduce the metabolic cost of climbing, these nighttime flights offer other benefits. Flying at night provides more stable, less turbulent air and may reduce the risk of predation from diurnal raptors.

GPS tracking and heart rate monitoring of bar-headed geese have shown that while many birds take advantage of lower-altitude mountain passes through the Himalayas, they don’t always follow the easiest routes. Some individuals ascend over high ridges, occasionally exceeding 7,000 meters in elevation.

The bar-headed goose isn’t the only bird with an impressive migration. Species like the demoiselle crane also undertake high-altitude journeys across the Himalayas. However, what sets the bar-headed goose apart is its reliance on constant flapping flight. While birds like the demoiselle crane conserve energy by soaring on thermal currents and updrafts, the bar-headed goose powers itself over the world’s tallest mountains with nearly continuous wingbeats.

This flight strategy might seem energetically costly, but constant flapping enables the geese to closely follow the contours of the terrain, taking advantage of wind patterns and potential drafting effects, according to research publish in Science. Surprisingly, this approach helps conserve energy, even though it requires the birds to repeatedly lose and regain altitude as they navigate the rugged Himalayan landscape.

The entire migration of the bar-headed goose spans over a thousand miles and takes around 80 days, but remarkably, the geese can cross the Himalayas in just a single day. This extraordinary high-altitude migration highlights the their unique physiological adaptations, offering valuable insight into how animals can evolve to overcome extreme environmental challenges.

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