The Bird that climbed Everest

You may not have heard of them, in fact I very much doubt you have, but I just want to say that the bar-headed goose is an absolute marvel of nature. This goose can fly over Mount Everest. That means they fly almost 9000 metres up in the air.

The bar-headed goose (Anser indicus). Image credit: Noel Reynolds (Wikimedia Commons)

"Whoop-de-doo" you might think. After all, they can fly so it shouldn’t be that hard.

Wrong! Flying is already tough enough as it is. I mean I can’t do it, can you? (and no planes do not count).

Flying is an incredibly tiring activity under normal circumstances, but this goose faces further adversity from chilly winds and oxygen starvation.

The only question now is 'how do they do it?'

The problem

A big problem with flying as high as the bar-headed goose does is that the air is very thin. But what does this even mean?

Mount Everest. Image credit: Ocrambo (Wikimedia Commons)

I'd like you to imagine that the air around you is a bag of chips and the chips inside are oxygen molecules. At sea level the air is packaged like a can of pringles, the oxygen is tightly packed and so you can pick up a lot in one handful (if they ever made the cans large enough to fit a hand). But when you get up as high as Mount Everest, your'e grabbing 'oxygen' from one of those dodgy chip bags that are full of empty space, so obviously you can only grab a few at once.

This is the goose's problem. Each time they breathe in they only grab a little bit of oxygen, nowhere near enough to fuel their arduous journey. That is, if they were a normal bird of course, but luckily these geese are far from average.

The breathing

One of their solutions is to breathe faster than other birds. 

But it's not that simple. When you breathe in more, you also breathe out more, causing you to lose a lot of carbon dioxide. The problem with that is that carbon dioxide is also what reminds us that we need to breathe in. Receptors in the brain are sensitive to carbon dioxide levels and tell us to breathe when these levels get too high.

That's why hyperventilation in humans is so dangerous. It takes us a long time to build up the carbon dioxide levels again to remind us we need to breathe. This is a strategy commonly employed by free-divers as a way to stay underwater for longer. Unfortunately, it can easily result in them falling unconscious from oxygen deprivation before they even realise they need to return to the surface to breathe. Put simply, you die because you don't realise you're dying.

The goose's solution to this problem is to blunt their sensitivity to carbon dioxide and instead become more sensitive to oxygen. That way they know to keep breathing as soon as their oxygen starts to run low.

The blood

Haemoglobin is the molecule vertebrates use to snatch oxygen out of the lungs and carry it through the bloodstream to fuel tissue. Quite probably the most crucial aspect of the bar-headed goose's success is one small change in their haemoglobin. It was a fluke really, one chance mutation altering just one amino acid (the building blocks of proteins) and all of a sudden their haemoglobin became the most effective oxygen-grabber around.

Haemoglobin. Gif credit: BerserkerBen (Wikimedia Commons)

The powerhouse of the cell

The mitochondria is the powerhouse of the cell. 

Even if you never did biology, this seems to be something that everyone's heard before. Mitochondria are a crucial component of any cell and they hunger for oxygen.

Mitochondria. Image credit: Pschemp (Wikimedia Commons)

The bar-headed goose's mitochondria aren't really any different to ours. What's special is where they put their mitochondria. Bar-headed geese stack all their mitochondria on the edges of their cells, as close as possible to the capillaries bringing in oxygen.

But why does this help?

Imagine you're catching a tram in the city. You cram into the door with everyone else but then spread out, cause let's be honest, you want your space. Oxygen does the same thing when it enters the cell. So being on the edge means that mitochondria can grab oxygen molecules before they spread out throughout the cell.

But why all the effort?

These geese breed in countries such as China and Mongolia, but they don't want to put up with the chilly winters there. So they fly south to the warmth of India or Tibet. Going over the Himalayas just happens to be the most direct route.

Why not fly around? or go somewhere else?

To be honest they probably could. Other areas are just as warm and even going around would work fine. The only real reason they trek the Himalayas is that it's what they've always done.

When the species first started to make this journey, the Himalayas weren't yet very high so it made sense to migrate over them, and now the geese are simply too stubborn to change.

Bar-headed goose in flight. Image credit Tsrawal (Wikimedia Commons)

You can find out more about the bar-headed goose here and here, because to be honest I've still barely scratched the surface in explaining the many remarkable traits these birds have that allow them to overcome the world's highest mountaintop.