As summer comes to an end and temperatures start to cool, birds of all kinds heed nature's call and head south to warmer climates. Some make incredible journeys that challenge the imagination. Ray Brown is the host of a radio show called "Talkin’ Birds." He spoke with WGBH All Things Considered host Barbara Howard about some birds that will be migrating this season. The following transcript has been edited for clarity.
Barbara Howard: You know, it seems kind of early. Has the migration actually begun?
Ray Brown: Migration of some sort or another began back in late June. Some shorebirds are migrating really early, and migration of various species will continue into December.
Howard: I understand hawks right now are in the midst of migrating.
Brown: Mid-September is probably the biggest time to see hawks migrating in this area.
The one we see the most in migration is the broad-winged hawk — they tend to form into these big flocks, what they call kettles, and are swirling around. So they're pretty easy to spot.
Howard: So they're not like geese, where they're in a V-formation?
Brown: Right, they're riding these thermals, which are kind of big circular risings of air. So they ride those thermals up, and when they get to a high lofty perch, they'll then glide down in the direction of travel.
Howard: So you won't see their wings flapping so much?
Brown: They hardly have to flap at all.
Howard: Now hawks are far from the only birds that are migrating. Tell me about some others.
Brown: There are probably 350 species in North America that migrate, and maybe 250 or so are what we call long-distance migrants. They're heading all the way down into the Caribbean, Central America, northern Central America. And some of them just do some flights that are almost hard to imagine. One of them is the Arctic tern. The amazing thing about the Arctic tern is that it migrates from the Arctic to the Antarctic. Now it breeds up in the Arctic, so you'd think, okay, breeding season is over, I'm going to head south. Which it does, but it doesn't head south to equatorial areas. It heads all the way down to Antarctica. So what it's doing in effect is spending two summers per year. It’s said the Arctic tern sees more daylight than any other creature on earth.
Howard: How big a bird is this to make the long trip?
Brown: The Arctic tern is maybe a foot long from the tip of the beak to the tip of the tail, has about a 30 inch wingspan.
Howard: And that's not even the smallest bird that makes such a long distance trip.
Brown: That's right. There's a bird called the blackpoll warbler that's especially noteworthy. It weighs a little bit more than a quarter, like the coin. It flies from New England — and in many cases from farther north, in western Canada — to a destination of the Caribbean Islands and Central America. So it flies over that open ocean without stopping, without feeding, without resting, mostly because it can't do any of those things. It can't land on the water, it would not survive. So it's able to fly these incredible distances, something like 1,700 miles nonstop over several days to reach that destination.
Howard: How is that possible — wouldn’t you just burn so many calories? How does it not just extinguish itself?
Brown: Sometimes it does, if it encounters some really tough weather conditions. But what they do, and what many of these long distance migrating birds do, is they fatten up before they go. Some birds actually double their weight and they can use those fat reserves that they gain in an incredibly efficient way.
Howard: What about climate change and other environmental impacts on migration?
Brown: Some bird conservation groups describe climate change as the number one threat to bird survival, and migration is certainly part of that. A big part of this claim is the idea that climate change can disrupt the timing of the birds in terms of their finding food when they come north in the spring, for example, because birds in large part are triggered by the changes in the available light. So in the spring, as the days get longer and in the fall as they get shorter, this actually causes hormonal changes, which triggers this urge to migrate. So that doesn't change whether there is climate change or not, but other conditions on the ground do change as a result of climate change, like the explosion of insects hatching in the spring, for example. So if the birds are coming when they always do, but the insects are hatching sooner, they're not going to be able to get the food that they normally would find, and this will have a big impact on their nesting.
Howard: So they're out of sync?
Howard: Well thanks, Ray.
Brown: Thank you, Barbara.
Howard: That's Ray Brown, talking about the fall migration. He hosts the radio show Talkin’ Birds. This is WGBH’s All Things Considered.