Why do birds migrate north for winter?

Colin has been looking skyward. He wants to know 'Why do birds bother to migrate and why do most species settle for winter in the southern hemisphere before going north for the summer?'

Eleanor - Okay. So this is a really, really great question. And so basically what a bird is looking for is it's looking for the right kind of conditions. It's looking for a place where it can feed, it's looking for breeding grounds. And so it will move depending on that. And so it depends on what hemisphere you're in. So if you're in the Northern hemisphere, you travel south and in the Southern hemisphere, you travel north. So it depends on where you are as to where the best place to be is for summer or winter.

Harry - And are there any bird migrations that really stand out to you?

Eleanor - Oh yes, absolutely. There's, I mean, there are so many wonderful, wonderful examples of incredible migrations, but for me the best one, oh, wait, wait, one of my top migrations would probably be the Arctic Tern. And now this incredible bird, it actually migrates from the Arctic summer. And then it follows the summer all the way down to Antarctica. And it does that every year. And the craziest thing is it doesn't also go directly. It takes a more kind of roundabout route. So you're ending up looking at a migration path of 30,000 kilometers, which is just an insane amount. In fact, it's such a big amount that I had to try and like kind of put that into perspective a little bit. And I looked up, there was a, there was a study that was done, I think in 2010, and it suggested that the average American walked about four kilometers a day, so that if you, if you kind of do the math, then this is the equivalent of this bird is moving every year, the equivalent to the average American, what they would move in about 20 years, which is, you know, it's just extraordinary for relatively kind of small little bird. It makes this incredible journey.

Harry - It's quite small as well, isn't it?, it's not a big bird.

Eleanor - No, it's a small bird. You're looking at something that's about 40 centimeters long. Um, so yeah, an incredible, yeah. And so that's, that's quite a lot smaller than the average American, which makes their, their feats even, even more incredible.