Why bother migrating?

Let’s consider migration - perhaps this brings to mind large mammals travelling across swathes of Africa. Or migrations that plunge into the water, from gargantuan blue whales to tiny zooplankton. So, why bother migrating at all, and how does it work? Phil Sansom asked Paul Walton from the RSPB...

Paul - I think it's really about two things. The first is survival. So for example, if you are an animal breeding in the Arctic summer, which is massively productive, there's lots of food around, there's lots of sunlight and that's great. But then when that summer is over, you've got kind of, nine months of ice and darkness, and very few animals can actually survive that. So it makes sense to move to other areas, where your survival chances are enhanced. So that's one thing. And I guess the other really big driver is the seasonality. Utilising temporarily available resources, in particular food. So there'll be blooms of algae, or blooms of insects, or fruits coming into season or seeds, for example, that are really there temporarily. And it's about moving to utilise those resources. I think broadly speaking, that's the drivers for these incredible movements.

Katie - Now, Paul, you're actually a seabird expert, aren't you?

Paul - Yeah, that's right. Yeah.

Katie - What are some of these journeys like?

Paul - Staggering, as far as seabirds are concerned, you know, here in Scotland, I worked in Shetland and Orkney, where there are breeding Arctic terns. Now the Arctic tern really is the longest distance migrant of any animal. So they go from the Arctic and sub-Arctic, where they breed, right down to the sort of, sub-Antarctic and Antarctic, but not just down to the bottom of the Atlantic, quite a lot of them go right round to the other site of Antarctica, which means they're actually going as far as they possibly could. They are going right round, literally halfway around the world, as far as they possibly could, before they come back. And one thing that really struck me is, working in Shetland, there's a midsummer in Shetland. It doesn't really get dark. The locals just called it the Simmer Dim. At night, it's just kind of like twilight, before it starts to get light again. So these birds are experiencing almost 24 hours of daylight when they're here breeding. But then of course it's the same when they go down South, and they're experiencing the Antarctic summer. So these are birds that really spend nearly all of their lives, in the light and in the air, it's quite beautiful really.

Katie - That's phenomenal. How do they know where to go?

Paul - That's a really, really good question. There's a mixture of things. So insects migrate, the Monarch butterflies over in the United States, that migrate down to just a couple of valleys in Mexico. And then there's our own Painted Lady butterflies. We've recently discovered they make a high altitude migration. Those animals, it's very unlikely there's any learned behaviour in there, it's instinctive. And I think for many birds, the corncrake is one bird that the RSPB has been studying for many years. It's got a complex migration pattern, that's only just emerged. But the birds only live for one or two years mostly. So their migration route is very likely to be an instinctive thing. For other animals, like the Arctic breeding geese. We know that they live longer and they hang out in family groups, sometimes for their whole lives. And it's very likely that young geese really need to learn the ins and outs of migration, not just the route to take, but the vital stopover points, where they can feed to make these long distance flights.