[SciShow Intro]
Hank Green:
    If you live in the Western Hemisphere, anywhere between southeastern Alaska and southern Chile, you've probably heard the telltale hum of one of the most awesome birds on the planet.
    Hummingbirds are the smallest member of the class known as Aves, ranging across more than 325 species, from South America's giant hummingbird, that's about 20 centimeters long, down to the tiny bee hummingbird, just 5 centimeters long, weighing less than a penny.
     You only have to see a hummingbird fly to know that they are different from other birds.
     You probably see 'em when they're feeding, sipping nectar from a flower or feeder, in which case you know that they can hover in place for a long time before darting off. Of course, their small size helps with this maneuverability, but they save even more weight by having only the bare minimum when it comes to legs and feet.
     Hummingbirds can't walk, or hop, or do any of the other land-based things that you see most other birds doing. They can only perch, and sorta shuffle from side to side, which is probably terribly cute, but this savings in body mass allows them to invest in bigger, more efficient hearts that can beat as much as 1200 times per minute.
     Their brains, meanwhile, account for 4.2% of their body weight, the largest proportion of any bird, which helps them remember where every flower in their territory is and how long each one will take to refill with nectar. Research has shown that they can even remember which individual human is the one who fills up their feeders.
    But these little dudes have brawn as well as brains. Because they need so much wing power to stay aloft, their pectoral muscles are, proportionally speaking, huge! Their pecs can account for up to 30% of their total body weight, a higher percentage than any other bird in the sky.
    And then we have their incredible wings. Now, all flying birds tend to have the same wing anatomy, basically, which is actually quite similar to the human arm. It's just that their bones differ in proportion and flexibility depending on the bird's size and lifestyle. Like, an albatross and a hummingbird have the same wing bones, but even if they were the same size, their wings would look very different. Albatrosses are set up to soar for long distances without flapping, so the parts of their wings that we might think of as their hands and fingers are very elongated; but hummingbirds have to move their wings constantly, so they have more length in their upper wing bones, especially the humerus, which connects to the shoulder.
    And the way these bones move is, anatomically speaking, just weird. Most birds flap their wings up and down, gaining all of their lifting power on the downstroke; but hummingbirds actually twist the bones in their shoulders and wrists so that they can stroke forward and backward and gain lift from both directions. Super-slow-mo studies of hummingbird flight show that their wings make little horizontal figure eights, which generate about 75% of the lift on the downstroke and another 25% on the upstroke, allowing the little guys to hover indefinitely.
    The results, as you probably know, are amazing. Having wings that pivot instead of flap allows hummers to immediately change direction: fly straight up, or go sideways, even backward. Of course, the downside to all this is that hummingbirds can't glide like larger birds, so these little fliers have to beat their wings much faster to stay in the air- like, as much as 200 times per second.  In this way, hummingbirds actually fly more like insects than birds.
    Of course, it takes a whole lot of energy to keep your heart beating and wings flapping at such speed, and for this, hummingbirds have another secret weapon: their metabolism. Although they do occasionally eat insects, hummingbirds' main jam, of course, is nectar, which is basically just straight-up sugar, and when a hummingbird eats, its muscles are able to immediately burn whatever sugars it just ingested, avoiding the energy-draining process of first converting sugar into fat so that the sugar goes right from their blood into their muscle tissue. As a result, hummingbirds can't really store fat. Instead, they burn sugar so fast that, if they were the size of me, they'd have to chug a can of soda nearly every minute just to get by- which is not something that I'd recommend for a human.
    Thanks for watching this SciShow Dose. If you'd like to learn more about all kinds of animals, check out our partner channel, Animal Wonders, at youtube.com/animalwondersmontana, and don't forget to go to youtube.com/scishow and subscribe, if you want to keep gettin' smarter.
[SciShow Outro]