Ospreys, also called sea hawk or fish eagle, are found all over the world including here in New Hampshire, But wherever they live, 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.
A project in New Hampshire is tracking Granite State birds and learning about the many misadventures they have between their departure in the fall and return in the spring.
Not too long ago if you wanted to learn where an Osprey goes when it migrates, you put a little band on its leg, but a band basically tells you where a bird is exactly twice, when you tag it, and when you recover it.
“Usually that’s a dead bird.” says biologist Rob Bierregard from the University of North Carolina, “So you know where the bird died, but you don’t know how it got there, you don’t know when it got there.”
That’s why over the last couple of years Bierregard has come up to the Squam Lakes Science Center in Holderness to help catch New Hampshire Osprey, and outfit them with little GPS equipped backpacks. The data that researchers have gleaned show that these Osprey have a lot of wild rides.
They are hard-wired to feel an irresistible urge to fly south based on evolution. Over the years the birds that didn’t have that urge starved, and their genes never got passed on.
“Some of them, the juveniles will just take off and just go, and they won’t stop until they reach South America,” says Iain Macleod, executive director of the Squam Lakes Science Center, “That hasn’t worked for any of the birds that we followed from New Hampshire, they’ve all ended up dying.”
One, 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 English Channel.
“He ended up closer to Portugal than he did to South America, before after a week of being out at sea he took off and ditched in the water,” explains Macleod.
Most Ospreys, especially once they are experienced adults, head down the coast, where they can rest and hunt along the way. Macleod says none of the birds he has watched have survived after flying straight South from New England, right out over the Atlantic Ocean, but it does happen.
Bierregard says he’s seen a surprising number of birds from places like Martha’s Vineyard survive that flight. “So they just go straight and it’s anywhere from 45 to 60 hours of non-stop flying” he explains, over a thousand of miles of open ocean, until they hit the Bahamas or Turks and Caicos.
While that is a tough flight, there are other dangers that kill more birds.
Some hit the Caribbean and think, this seems like a nice place for the winter.
“Which it turns out is so far invariably a fatal mistake,” says Bierregard. Every osprey he has tracked who tries to winter on the Dominican Republic has been shot. “They shoot them because they’re not good raptor ecologists. They love chickens, so anything they think will eat chickens they shoot.”
Of course osprey 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.
“Going across the Caribbean from Hispaniola to South America is more dangerous than a thousand miles across the Atlantic because they’re doing it in the middle of Hurricane Season,” says Bierregard.
This is where experience comes in.
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. “He’s got life knowledge, he knows what’s ahead of him,” posits Macleod, “whereas the juveniles are just flying blind, they have no clue what’s on the other side of the Caribbean and that it’s a 400-mile flight! It’s just, ‘I’ve got to go south!’”
Donovan spent a while fattening up in Puerto Rico, and then successfully crossed to Venezuela. “That was fascinating to see that sort of decision making,” says Macleod, allowing himself a momentary lapse in strictly scientific thinking, “And I’m sort taking a leap of presuming what’s going on but that just sort of seems to make logical sense.”
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. “Their little program in their brain says go North and stay over land whenever possible,” he explains.
They head North and find Cuba, then Florida and suddenly they’ve learned the way.
“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,” Bierregard chuckles.
After that first migration, mortality drops from as high as 75 percent, to around 10 percent among adults.
The technology required to track these birds continues to get smaller, and as it does Bierregard says researchers will start outfitting even smaller birds and learning their stories.