Researcher Mason Maron holds a red crossbill — a species of finch — at Wenas Creek near Yakima, Washington. (Jeff Kozma/Contributed Photo)

The proliferation of lesser goldfinches is an indicator of environmental changes in the Columbia River Basin

Mason Maron grew up west of the Cascades. When he moved east to Pullman, Washington, in 2019 to attend Washington State University, one of the unfamiliar birds he encountered there was a small, noisy, yellow songbird called the lesser goldfinch.

“I assumed that they were just part of the bird diversity there,” he said.

Then a local birdwatcher told him that lesser goldfinches were actually a new development in the area.

“Five, 10 years ago there were no lesser goldfinches in the area at all,” Maron said.

Today flocks of lesser goldfinches are common in many areas of the Columbia River Basin.

A few decades ago, however, they were almost unknown in the Pacific Northwest outside of the Willamette Valley. Look at the map of the species’ breeding range in a field guide and you’ll see it depicted primarily in the American Southwest.

A new study led by Maron takes a deeper look at this expansion and shows the northern edge of the birds’ range has shifted by more than 260 miles in the last two decades — driven, apparently, by changes in both climate change and land use.

Maron was intrigued by the mystery of Pullman’s lesser goldfinches but didn’t have the skills to investigate deeply as an undergraduate. Once he finished his bachelor’s degree in 2023, however, inspiration struck.

“I was looking for ways to conduct research before starting a grad school program, and that idea came back up in my head,” he said. “I thought, maybe I can look into this now.”

He began collaborating with two other ornithologists to analyze lesser goldfinch data from Project FeederWatch, an annual bird survey in which volunteers collect and submit counts of the birds in their yards.

Focusing on data from 2001 to 2023, Maron and his colleagues were able to determine not only how far north the birds had spread in that time, but also the factors that determined which local habitats they moved into.

The results showed the finches preferred to move into areas with warmer temperatures, higher rainfall, urban development and proximity to major rivers.

“[These associations] are really important to identify,” Maron said, “because not only do they tell us more about how the birds got to this point, they can tell us something about where they might go from here.”

Important contributions

Lesser goldfinches feast on the seeds of weedy, invasive plants such as thistles and dandelions, which are abundant in the Pacific Northwest in disturbed, urbanized areas such as roadsides and vacant lots — and along the rivers the birds have used as corridors to reach new areas.

Although past studies have associated range expansions of other North American birds with the resources provided by backyard bird feeders, Maron’s data suggests that this isn’t the case for lesser goldfinches. (Despite the name, Project FeederWatch data includes surveys from sites where there are no bird feeders.)

Once lesser goldfinches arrive in a new place, they tend to stick around. According to data from the citizen science platform eBird, since 2012 their numbers have increased by 17% in Oregon, 66.3% in Idaho and 110% in Washington.

“This is a very nice study that clearly shows the process by which species are shifting their distributions across the world in response to ongoing anthropogenic transformation of the environment,” said Morgan Tingley, an ornithologist at the University of California, Los Angeles, and an expert on long-term changes in bird populations. Tingley was not involved in Maron’s study.

Maron’s study adds to previous research that has documented dramatic range shifts in other North American bird species including northern mockingbirds, Carolina wrens and Anna’s hummingbirds.

The reason, according to Tingley and Maron, is likely a mix of changes in climate and land use, such as urbanization.

“(This) highlights a common theme when scientists study species changing over time, which is that the attribution of phenomenon to particular drivers is very challenging,” Tingley said.

At the same time that lesser goldfinches have exploded into the Pacific Northwest, they’ve been declining in their historical range.

In Utah, for example, their numbers are down about 6% during the last decade. As the world changes around them, they aren’t so much expanding their range as shifting their strongholds northward.

If lesser goldfinches can adapt to changes in their habitat by moving into more hospitable areas, is this good news?

For the time being, it seems to bode well for the survival of the species.

But if they’re moving because the habitat that they historically occupied is becoming less habitable, that’s not a positive sign about the health of the natural world, according Maron, who is starting a graduate program at the University of Illinois Urbana-Champaign in the fall.

“The shrubby riparian habitat that they enjoy doesn’t go on forever,” he said. At some point, “they will run out of places to go.”

—  Rebecca Heisman is a freelance science writer based in Walla Walla. She is the author of the 2023 book “Flight Paths: How a Passionate and Quirky Group of Pioneering Scientists Solved the Mystery of Bird Migration.”

— Columbia Insight, based in Hood River, is a nonprofit news site focused on environmental issues of the Columbia River Basin and the Pacific Northwest.