They come from far north every year, flying non-stop over Mount Everest—almost nine km up in the air, settling down at different locations in India after crossing the Line of Control at different places. To get here, the bar-headed geese fly over Mount Everest, which rises to 29,035 feet (8,850 meters). Researchers have found that the geese reach an average height of nearly 21,120 feet (6,437 meters) during their travels.

The migration takes about two months and a distance of up to 5,000 miles (8,000 km) is covered but the last leg of 1,000 km over the Himalayas is covered in eight hours of non-stop flying. The bar-headed geese arrive in India in November and go back to their breeding areas around mid-March. According to Migrant Watch Data, the species is usually first sighted across the northern pains in Nov-Dec and in south India in Dec-Jan.

George Lowe, the New Zealand born climber who supported Edmund Hillary and Tenzing Norgay's ascent in 1953, claimed that he had seen the geese flying over the top of Mount Everest: "Geese tend to honk a lot as they fly…” Lowe wrote, “the distant honking of these birds flying miles above me unseen against the stars.”

The bar-headed geese are unlike any other species of water fowl. Characterised by a slender build, steel grey plumage, yellowish bill and a white head with two black bars, they are a sight to behold. Bar-headed geese, in India they are known as Raj Hans. In Indian mythology, the bar-headed goose is referred as <em>Hamsa</em> and in another interpretation, this is likely to be <em>Kadamb</em> in ancient and medieval Sanskrit literature where <em>Hamsa</em> generally refers to the swan.

The first time I observed them was in Bharatpur sanctuary in Rajasthan in 2018 and they have been my favourite bird species ever since. Since then, I have seen in them wetlands of NCR, the Chambal Biodiversity Park and reports suggest these have been sighted in other major wetlands as well. In NCR, the Sultanpur lake is one of their favourite places. An adult goose weighs about three kg and stands about two feet high. Two horizontal black stripes on the back of the bird's white head give the species its name. The pretty birds don't look super athletic yet they fly so high.

Decades of research showed that the bar-headed geese are level-headed about their gruelling trip from their breeding areas in Mongolia, the Tibetan Plateau and northern China to India. They fly over the Himalayas using less than ten per cent of the oxygen available at sea level, reaching altitudes of up to 9,000 m with no help from tailwinds. No oxygen? No problem. Instead of climbing to dizzying altitudes and flying in a straight line over the mountain tops, they follow a “roller-coaster” route.

Humans who climb the Himalayas acclimatize or use an oxygen mask. The bar-headed geese, however, use oxygen efficiently. According to Salim Javed, noted ornithologist who documented the migration of these birds, the geese fly in a rarefied atmosphere due to physiological adaptations—a large heart which beats extraordinarily fast and haemoglobin with a remarkably high affinity to oxygen. This makes it possible for the bird to take on high-altitude flights without needing time to acclimatise.

Also, their wings are large and they are powerful flappers. Earlier, scientists thought the geese were taking advantage of daytime winds that blow over mountaintops. But they found that the birds prefer to fly at night, when conditions are relatively calmer. Temperatures are also colder in the night, making the air denser. Denser air carries more oxygen and increases the lift that the birds' wings generate. These birds complete the ascent under their own muscular power, with almost no aid from tail winds or updrafts. The bird is clearly a star migrant that is built to fly high. Though the birds take frequent stops during the migration, they cover the Himalayas in a single effort of about eight hours with little or no rest. A similar intense climb could kill a human without proper acclimatization.

Despite their dangerous flying across the Himalayas, the perennial threat from the H5N1 virus spreading virulent bird flu, predation, game hunting and poaching in Asian countries, there are a number of organisations working on conservation. The Union Ministry of Environment developed a national action plan for the conservation of migratory birds and their habitat for years 2018-2023 to meet national commitments under international conventions—Convention on Conservation of Migratory Species of Wild Animals (CMS), the Convention on Wetlands of International Importance especially as waterfowl habitats (Ramsar), the Convention on Biological Diversity (CBD), and the Convention on International Trade of Endangered Species (CITES).

Why it chooses to fly over the highest peaks instead of using lower passes is a question about which a research says: “The bar-head geese have done that migration for millions of years, even before the Himalayas were as tall as they are now. The birds have been forced to fly higher as the mountains have moved higher.”.