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In 1973, an airliner struck a bird called a Ruples Griffin vulture, which on its own isn't that weird. Planes hit birds pretty regularly during takeoffs and landings. But this collision happened at a cruising height of over 11,000 m. That's way above the height at which most birds fly, which it makes me wonder, what is the highest a bird can actually fly. Hi, I'm Cameron and this is Minute Earth. Birds don't tend to fly higher than they absolutely need to for the same reason you don't sprint when you could walk. It's difficult and tiring. So, we can't necessarily get the answer to this question through observation. I mean, I guess we could drop a bunch of birds out of airplanes and see what happens, but our AdSense
revenue definitely isn't going to cover that. Plus, we're not monsters. So, let's use our understanding of aerodynamics, scaling laws, and biology to science our way to an approximate answer. There are two things that limit how high a bird can fly. Its ability to stay aloft as the air pressure decreases. And on a much more basic level, its ability to stay alive as the temperature and amount of oxygen decreases. So, first, let's figure out which bird could survive at the highest altitude. Oxygen supplies birds the energy they need to stay warm, but at higher altitudes, there's less oxygen available and the temperature is much colder. So, a bird's ability to survive high up in the air depends on how
efficiently they use oxygen and how well they can retain body heat. This paper measured the oxygen use of a handful of birds and found that very generally their overall oxygen use increases with mass. We can then adjust according to other traits like how much energy their flight muscles require and how much insulation their feathers provide. From all of this, we can calculate the altitude at which each bird should suffer from hypothermia. Let's call this their popsicle point. If we then compile a data set of flying birds and plug their data into these equations, we can see a general pattern emerge. Larger birds can theoretically survive at higher altitudes than smaller birds.
There are exceptions, of course. This is biology after all, but our calculations suggest that there are a bunch of birds that could potentially survive above 10,000 m. And the largest bird in our data set, the wandering albatross, might be able to survive as high as 17,000 m. But remember, we also need to figure out if any of these birds could actually stay aloft at such high altitudes. Because the air is less dense the higher you go, less air is available at higher altitudes to push upward against a bird's wings and create that lift. A bird's ability to stay a loft high in the air depends on its weight, size of its wings, and the shape and angle of attack of its wings. That's a factor
called the lift coefficient. Combining all of that tells us how much lift a bird's wings should generate in still air at a given altitude. Simple enough at first. Uh, but while weights and wingspans and whatnot are easy enough to measure, the wing shapes and angles aren't because a bird's wing shape changes as it flies. I'll save you the long explanation of my rationale here and just say that this is about where I go out on a bit of a limb. The lift coefficient for the birds in our data set peaks at about 1.5 or so, and that's when they're taking off or about to stall. In other words, when the bird is trying hardest to generate lift. And since staying aloft is likely a struggle
at a bird's maximum altitude, this is probably a pretty good estimate of the lift coefficient at this point. From there, we can find the lowest air pressure at which each bird could generate sufficient lift to keep its mass aloft. And then use our friend, the barometric equation to convert those numbers to altitudes to estimate the highest point each bird in our data set should be able to actually maintain flight. Let's call this their lift limit. In general, the smaller birds have the highest lift limits. The hulking mute swan would struggle to generate lift at a mere 3,800 meters, while the puny sand martin should be able to glide at nearly 19,000 m. Of course, air moves and it's not uniformly dense at given altitudes, so there's
definitely some wiggle room here, which will be a surprise tool that's going to help us later. But in any case, a bird with a higher lift limit should be able to fly higher than a bird with a lower one. Now, let's combine our lift limit data with our popsicle point data. We can see that lots of birds like the missile thrush can theoretically fly super high but would freeze long before they got there. And then there are a bunch of other birds like the wandering albatross that could likely survive at super high altitudes but wouldn't be able to actually maintain flight up there. That leaves us with a small cluster of birds with relatively high popsicle points and high lift limits.
Mathematically, these should be the highest flying birds. And for the most part, they're geese. The grey lag goose, the bean goose, the Canada goose, and the barheaded goose should be able to fly as high as 8,000 meters or so, according to our calculations. And this matches up pretty well with what scientists have actually observed. Like during its migration over the highest mountain range on the planet, the bar-headed goose can reach altitudes of over 7,000 m. And then there's the white str, which based on its popsicle point and lift limit, is our predicted highest flying bird. It could potentially fly up to about 10,500 m. In reality, it doesn't fly anywhere near that high. But
remember, birds don't necessarily fly as high as they might be physically capable of. But wait, what about the Ruples Griffin? A bird we know for a fact can fly higher than 11,000 m. Our math suggests that it is lift limited a lot lower than that, about 8,200 m. But this is where theoretical calculations fall short without some additional real world knowledge. See, the Ruples Griffin likes to soar on thermals, warm columns of rising air that can help birds exceed their mathematical lift limit, sometimes even thousands of extra meters up into the air. Other birds are also known to ride thermals, but none of the other high popsicle point birds ride such supercharged thermals. So, the Ruples
Griffin is likely the bird capable of the highest flight. With the right thermal, it might even reach its very generous popsicle point of 15,000 meters. Turns out that bird might have had a lot of climbing left to do. You might have noticed that this video is chalk full of all sorts of calculations that I basically ripped my hair out trying to make sure I got right. It would have been great if I had a brilliant tutor sitting next to me guiding my learning. Wait, there is a brilliant tutor. If you regularly watch our videos, you're probably aware of the awesome interactive learning platform that is Brilliant. Now, Brilliance lessons are guided by a super intelligent personal tutor for math and
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