For an olive-sided flycatcher, the migration can be a marathon. Some of the sooty songbirds travel more than 15,000 miles a year, flying from South America to Alaska and back again. It’s a staggeringly long journey for a bird that weighs just over an ounce.
“Alaska olive flycatcher populations are just on this razor-thin margin of what is biologically possible,” said Julie Hagelin, a wildlife research biologist with the Alaska Department of Fish and Game and senior research scientist at the University of Alaska Fairbanks.
To survive the long journey, the birds need safe places to rest and refuel. But the locations of these “little utopias” have been a mystery, Dr Hagelin said. So in 2013, she and her colleagues set out to unravel it by following the birds. They hoped that identifying the crucial stopover sites could provide clues to why olive flycatcher populations are declining and what might be needed to save them, including where experts should focus their conservation efforts.
The investigation turned out to be more difficult than they expected. Olive flycatchers often breed in buggy swamps. They sit on the tops of trees. And they are elusive, scarce in the landscape and difficult to catch. “After the first year of struggling with this project, it became very clear why no one in their right mind would want to try to study this bird,” said Dr. Hagelin.
Here’s what scientists needed to get the data:
Make a lure
Olive flycatchers can be very sensitive to intruders in their territory, so the scientists lured the birds with fake bird rivals. They bought wooden bird decoys on eBay and then painted white spots on the flanks to mimic the flash of white feathers that males often display when agitated. “It’s kind of a long-range ‘Stay away’ or ‘This is my place’ signal,” said Dr. Hagelin.
Catch a flycatcher
The researchers attached the decoys to small trees or tied them to large sticks that stood upright in the soft soil. They hung fine mist nests and played flycatcher sounds from loudspeakers hidden in the bushes below the decoy. The scientists hoped that if a real flycatcher was nearby, it would fly towards the wood intruder and end up in their nets. Some birds did just that and responded quickly to the decoy. But sometimes it can take hours to catch just one flycatcher. “Maybe two, if we’re lucky,” said Dr. Hagelin.
Add a tag
The researchers used clear plastic cord — designed for making beaded jewelry — to make tiny flycatcher harnesses, each fitted with a geolocator tag. Once they had a bird in hand, they slid the loops of the harness over its legs, placing the tag against its lower back.
As the birds flew south for the winter, the geolocator tags regularly recorded light levels and time, allowing the scientists to estimate the approximate latitude and longitude of each bird. In later years of the research, they moved to using GPS tags, which can provide more accurate location data.
Do it again a year later
To download the data, the researchers had to recapture the same birds the following summer. “Retrieving this information added to my gray hair,” said Dr. Hagelin. The second time around, the birds were more wary and less responsive to the scientists’ trickery, so the researchers spent hours watching flycatcher nests.
“You can start to see patterns, such as locations or directions where the birds tend to leave or enter the nest, and how they move through the trees,” said Dr. Hagelin. “So you can put a net in the way and hope you catch them that way.”
Fingers crossed
Over the course of the five-year study, the researchers managed to deploy 95 tags. They recovered 17 geolocator tags, but only five GPS tags — and three of the GPS tags failed, providing no data at all for reasons the scientists still don’t understand. “That was really devastating,” said Dr. Hagelin.
“But all was not lost,” she added. The geolocator data pointed to 13 key stopovers, from Washington to southern Peru, plus three key wintering grounds in South America, the researchers reported in 2021. Tagging technology has improved, so scientists with a hunger for capturing flycatchers could now focus on collecting more detailed data about those locations. “Am I the person to do it?” said Dr. Hagelin. “Maybe if I had the funding.”