In homage to my daughter, I will say that Miley Cyrus had it right…it’s the climb. In this case, by Bar-headed Geese.
Bar-headed Geese journey each breeding season from India, which is at sea-level, up over the Himalayan Mountains, on their way to Asia. That is quite a trek for a little breeding.
The journey is long, but more interestingly it is high. Bar-headed geese fly over the tallest mountains in the world. These are mountains where the air is so thin that avid climbers die on their peaks. The bodies largely remain there because it is too strenuous to bring them back down, given the available oxygen, and the air is too thin to support things like helicopter flight. Yet, the geese make it not only to the tops of the mountains, but over them.
It was long thought that the geese used tail winds to push them up and over the peaks. But, now with the advent of satellite tags, placed directly on the geese, we know that they pump their way up and over all by themselves. They fly when the winds are calm. They can travel up the peaks at amazing speeds of 1.1 vertical kilometers per hour. They can go from sea-level up and over a peak of 6000 meters in just 7 or so hours.
So, how do they do this? They have a larger than average wingspan for their size. That means more lift when they fly. They have a special form of hemoglobin in their blood. Hemoglobin is the molecule that carries oxygen and gives our blood the characteristic red color. It is an iron-based molecule, which is why iron is so important in our diets. The goose’s hemoglobin allows them to pull available oxygen from the air better than you and I, or any other bird or mammal for that matter. And, they breathe more deeply and more efficiently under low oxygen conditions.
You’d think with that kind of ability such a species would be protected from almost any kind of threat. But, Bar-headed Geese were, sadly, also one of the first victims of avian flu. On their nesting grounds their eggs are prone to predation by foxes and other small mammals as well as ravens and seagulls. And, females even raid the nests of other females. So, while they a high-fliers in one respect, in other areas they are just another goose.