Ospreys, also called sea hawks or fish eagles, are found all over the world. But when the temperature drops, the birds head for the tropics.
For juveniles, that first migration is a crucible that only 25 to 40 percent survive.
From the Here & Now Contributors Network, Sam Evans-Brown of New Hampshire Public Radio brings this story of a project that tracks ospreys to learn about the adventures they have between their departure in the fall and return in the spring.
- Sam Evans-Brown, environment and education reporter at New Hampshire Public Radio. He tweets @SamEB_NHPR
JEREMY HOBSON, HOST:
You know, I was in Asia, and I was therefore lucky enough to miss the polar vortex, very happy about that. And I am not the only one. Ospreys also missed it because they like to spend their winter in the tropics. These birds are found all over the world, but when the temperature drops, they flee, and only 25 to 40 percent survive the migration.
From the HERE AND NOW Contributors Network, New Hampshire Public Radio's Sam Evans-Brown has the story of a project that tracks ospreys to learn exactly what happens between their departure in the cold and their return in the spring.
SAM EVANS-BROWN, BYLINE: Not too long ago, if you wanted to learn where an osprey goes when it migrates, you'd put a little band on its leg. But as biologist Rob Bierregard from the University of North Carolina says, a band basically tells you where a bird is exactly twice: when you tag it and when you recover it.
ROB BIERREGARD: Usually that's a dead bird. So you know where the bird died, but you don't know how it got there, you don't know when it got there.
EVANS-BROWN: That's why over the last couple of years Bierregard has come up to the Squam Lakes Science Center in Holderness, New Hampshire to help catch ospreys and outfit them with little GPS-equipped backpacks. The science center's executive director, Iain Macleod, says those GPS show that these osprey have a lot of wild rides.
IAIN MACLEOD: Some of them just, the juveniles will just take off and just go.
EVANS-BROWN: Ospreys are hardwired with an urge to fly south. It's all based on evolution. Over the years, the birds that didn't have that urge starved, and their genes never got passed on.
MACLEOD: And they won't stop until they reach South America. That hasn't worked for any of the birds that we followed from New Hampshire; they've all ended up dying.
EVANS-BROWN: One osprey called Chip ended up way off course. He got caught up in some weather and landed on a ship, which was unfortunately headed for the Europe.
MACLEOD: He ended up closer to Portugal than he did to South America before - after a week of being out at sea, he finally, you know, took off and ditched in the water.
EVANS-BROWN: Macleod says none of the birds that he has watched have survived after flying straight south from New England, right out over the Atlantic Ocean, but that doesn't mean it doesn't happen. Bierregard says he's seen a surprising number of birds from places like Martha's Vineyard survive that flight.
BIERREGARD: So they just go straight, and it's anywhere from 45 to 60 hours of nonstop flying.
EVANS-BROWN: They fly over thousands of miles of open ocean until they hit the Bahamas or Turks and Caicos. And while that's a tough flight, there are other dangers that kill more birds. Some hit the Caribbean and think, well, this seems like a nice place for the winter.
BIERREGARD: Which it turns out is so far invariably a fatal mistake.
EVANS-BROWN: Every osprey that he has tracked who tries to winter on the Dominican Republic has been shot.
BIERREGARD: And they shoot them because they're not good raptor ecologists. They love chickens, so anything that they think will eat chickens they shoot.
EVANS-BROWN: Let me just reiterate here: Ospreys eat fish, not chickens. But what Macleod and Bierregard have learned with all this tracking is the biggest hurdle for the birds is actually the Gulf of Mexico's weather.
BIERREGARD: Going across the Caribbean from Hispaniola, Haiti, Dominican Republic, to South America is more dangerous than a thousand miles across the open Atlantic because they're doing that in the middle of hurricane season.
EVANS-BROWN: This is where experience comes in. Most ospreys, especially once they reach adulthood, head down the coast, where they can rest and hunt along the way. Macleod points to another bird he calls Donovan, who attempted to cross the Caribbean from St. Croix. It seemed like he was getting blown off-course, so he turned around.
MACLEOD: He's got life knowledge, he knows what's ahead of him, whereas the juveniles are just flying blind. They have no clue that they've got to - you know, what's on the other side of the Caribbean, that it's a 400-mile flight. They just, oh, I've got to go south.
EVANS-BROWN: Donovan spent a while fattening up in Puerto Rico and then successfully crossed to Venezuela.
MACLEOD: You know, that was fascinating to see that sort of decision making. And again, I'm sort of taking a leap of presuming what's going on, but that just sort of seems to make logical sense.
EVANS-BROWN: But if birds can survive their first hazard-filled trip south, on the trip north Bierregard says they seem to follow a pretty simple algorithm that teaches them the proper route.
BIERREGARD: Their little program in their brain says go north and stay over land if at all possible.
EVANS-BROWN: They head north and find Cuba, then Florida, and pow, they've learned the way.
BIERREGARD: I jokingly say they track down their parents and ask them why they didn't tell them that they didn't have to fly over 1,200 miles of open water to get to South America.
EVANS-BROWN: After that first migration, mortality drops from as high as 75 percent to around 10 percent among adults. The technology required to monitor osprey continues to get smaller, and as it does Bierregard says researchers will start outfitting even smaller birds with GPS and learning their stories. For HERE AND NOW, I'm Sam Evans-Brown. Transcript provided by NPR, Copyright NPR.