Why aren't my parakeets blown from their perch?

Toby - There's a short answer and a long answer. The short answer is that they are clinging on. They cling on with their feet, which are like claws. So they grab onto their perch and by doing that they stay. But I think it's a very interesting question because I think we balance in quite a different way to the way they balance. So when we balance, we have to use our weight because our feet press down on the ground and the ground presses up on our feet. The way we balance is we move our centre of gravity, where the force of gravity acts on us, to counteract any forces on us. So if the wind blows, we brace ourselves by moving into the direction of the wind. And what we're doing is we're moving our weight out over our feet to create a counter rotation to the one that the wind is imposing on us.

Birds are very light, so they have very little weight. And so they can't do that. And presumably that's why they've evolved feet that can grip onto things. So they can exert forces by pushing and pulling, which we can't, whether you are large or small, if the wind is strong enough, it will blow you over. So, when you jump out of a plane, if you're not wearing a parachute, or rather if you're wearing a parachute and you choose not to open it for a while, you'll reach terminal velocity, which is a bit over a hundred miles an hour. And that's when the wind force on you balances your weight. Because we use our weight to balance against things like the wind, once the wind gets up to a hundred miles an hour or so, we can't use our weight effectively. And if we're not grabbing onto something, we will get blown down.