For an olive-sided flycatcher, migration can be a marathon. Some of the soot-colored songbirds travel more than 15,000 miles a year, winging their way from South America to Alaska and then back again. It’s a dizzyingly long journey for a bird that weighs just over an ounce.

“Alaska populations of olive-sided flycatchers are just on this razor-thin margin of what’s biologically possible,” said Julie Hagelin, a wildlife research biologist at the Alaska Department of Fish and Game and a senior research scientist at the University of Alaska Fairbanks.

To survive the long trip, the birds need safe places to rest and refuel. But the locations of these “little utopias” were a mystery, Dr. Hagelin said. So in 2013, she and her colleagues set out to unravel it by tracking the birds. They hoped that identifying the critical stopover sites might provide clues about why olive-sided flycatcher populations were declining and what might be needed to save them, including where experts should target their conservation efforts.

The research proved to be more difficult than they had bargained for. Olive-sided flycatchers often breed in buggy bogs. They perch at the tops of trees. And they are elusive, sparse on the landscape and difficult to catch. “After the first year of struggling with this project, it became really, really clear why nobody in their right mind would want to try and study this bird,” Dr. Hagelin said.

Here’s what it took for scientists to get the data:

Make a lure

Olive-sided flycatchers can be highly sensitive to incursions into their territory, so the scientists lured the birds with fake avian rivals. They bought wooden bird decoys on eBay, and then painted white patches on the flanks to replicate the flash of white feathers that males often show when they’re agitated. “It’s kind of a long distance signal of ‘Keep away’ or ‘This is my spot,’” Dr. Hagelin said.

Catch a flycatcher

The researchers attached the decoys to small trees or tied them to large sticks that were positioned upright in the soft ground. They strung up fine mist nests and played flycatcher calls from speakers hidden in the bushes underneath the decoy. The scientists hoped that if a real flycatcher was in the area, it would fly at the wooden interloper and wind up in their nets. Some birds did just that, responding quickly to the decoy. But sometimes it could take hours to catch just one flycatcher. “Maybe two, if we were lucky,” Dr. Hagelin said.

Attach a tag

The researchers used clear plastic cord — designed for making beaded jewelry — to fashion tiny flycatcher harnesses, each bearing a geolocator tag. Once they had a bird in hand, they slipped the loops of the harness over its legs, positioning the tag against its lower back.

When the birds flew south for the winter, the geolocator tags regularly recorded the light levels and the time, allowing the scientists to estimate each bird’s approximate latitude and longitude. In later years of the study, they transitioned to using GPS tags, which can provide more precise location data.

Do it again a year later

To download the data, the researchers had to recapture the same birds the next summer. “Recovering this information added to my gray hairs,” Dr. Hagelin said. The second time around, the birds were warier and less responsive to the scientists’ trickery, so the researchers spent hours watching flycatcher nests.

“You can start to see patterns like locations or directions that the birds tend to exit or enter the nest and how they’re moving through the trees,” Dr. Hagelin said. “So you can put a net in the way and hope you’ll catch them that way.”

Cross your fingers

Over the course of the five-year study, the researchers managed to deploy 95 tags. They recovered 17 geolocator tags but just five GPS tags — and three of the GPS tags failed, providing no data at all for reasons the scientists still do not understand. “That was really devastating,” Dr. Hagelin said.

“But all was not lost,” she added. The geolocator data pointed to 13 important stopover sites, from Washington to southern Peru, plus three main wintering areas in South America, the researchers reported in 2021. Tagging technology has improved, so scientists with an appetite for flycatcher catching could now focus on collecting more detailed data on those locations. “Am I the person to do it?” Dr. Hagelin said. “Maybe if I had the funding."

Emily Anthes is a reporter for The Times, where she focuses on science and health and covers topics like the coronavirus pandemic, vaccinations, virus testing and Covid in children. More about Emily Anthes

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