Since three local scientists studying golden eagles started trying to catch the birds in October — to swab them for DNA and pathogens and release them with a GPS transmitter attached — they've gone through 6800 pounds of bait meat.
"We've enhanced the landscape with three tons of food," said Robert Fisher. "It's a giant bird feeder — with cow."
Fisher, Jeff Tracey, and Peter Bloom are in the early stages of catching the eagles, gathering DNA to add to a broad western database of such eagles, and using the GPS data to track the birds. So far, the early data that shows the birds' location every 15 minutes already challenges our notions. These birds travel.
One sequence shows a bird that starts its day on Otay Mountain, travels north along the Sweetwater corridor to the San Diego River corridor, and on north until it reaches Palomar Mountain. And then the bird finds its way back to Otay Mountain in a day or two. Another heads north, avoiding Ramona, still making it all the way to Guejito Ranch.
All the data is early and inconclusive, since the study just began. But what the scientists have learned about the mechanics of doing such a study is surprising.
"A lot of science is people doing a lot of mundane things and hoping some glimmer of useful information will come from it," Tracey said. "Us? We're learning far more about hauling meat than we ever anticipated."
So far, they've caught seven birds — five females and two males — mostly in South County. Their goal is to catch and track 20. Golden eagles are civilization-shy. They hunt live prey, mostly rabbits and squirrels, but will eat carrion when prey is hard to find. They live about 30 years and stay with their mates for a long time, Tracey said. The birds like to keep territory and a network of nests within that territory.
Much of the information about where they've nested in the past was gathered by egg collectors — people who found the nests and took eggs, a method unthinkable by today's standard that probably contributed to the small numbers of birds now.
"There are 334 sets of [two] eggs that we know about that were collected [in San Diego] between 1884 and 1959," Fisher said. "We have no idea how many eggs were collected that weren't archived or put in a museum somewhere."
The new approach, of catching, attaching, and releasing the birds has its own risks.
"Golden eagles are super dangerous. They have really scary talons — a misstep and your guts are hanging out," Fisher said.
The team has been working mostly in South County, particularly around Otay Mountain.
"We're in meat management," Fisher says. "How do you keep meat on the landscape? Rebar." Tracey says the team sets up a rebar cage to hold the raw meat down and then, after they've watched the eagles eat in the spot a few times, a trap is sprung by someone watching the bait on remote camera. It takes time for eagles to see the spot as a reliable meal.
The birds only started dining at the traps in mid November, Tracey said. But other animals weren't so shy. Feral pigs cleaned out the bait by Barrett Lake. Pumas cleaned out another trap. Bobcats and skunks put in guest appearances.
"And hundreds of coyotes, of course," Fisher says. "We had to feed the coyotes as much as they could eat to get them to leave the bait alone."
The seven birds they've caught were healthy — if upset, Fisher said.
"We have watched pairs where we caught the female and the male saw it and it got really difficult to catch the male," he said. "We haven't caught as many as we want to."
The early travel data have been pretty surprising. The birds' territory appears to be far larger than expected, from 45 square miles to 340 square miles traveled by one of the females. And they avoid places, like Ramona.
"They stay in areas that have a high degree of wildness — the urban edge is really defining their territory, you can see it," Fisher says.