It’s beautiful, ethereal: When we hear the sound of the Swainson’s thrush in the Pacific Northwest’s woods, we know our summer is truly here. Our bird is back, with its signature song gracing our long, summer twilights.
And yet, this is not really “our” bird at all. It is a bird of two worlds. Arriving here by late May for its mating season, the Swainson’s thrush is gone by the end of September to its overwintering grounds, as far south as Central and South America.
Like all long-distance migrants, it faces a perilous journey.
For this is a bird that must contend with the combined effects of changes throughout its range, including loss of habitat to development, logging, agriculture and climate change.
The Swainson’s thrush has declined along parts of the Pacific Coast and elsewhere, and it could be vulnerable to loss of habitat. Other signature migratory birds of the Northwest are in trouble. The rufous hummingbird is in steep decline. Its population has cratered by 65% since the 1970s, and the rate of loss is accelerating, due in part to climate change and loss of habitat, scientists have found.
The Seattle Times traveled to two places to get a closer look at the Swainson’s thrush: the H.J. Andrews Experimental Forest, east of Eugene, Ore., and Costa Rica.
The Swainson’s thrush is known very differently in Central America.
“We call it the gray mouse,” said Luis Sandoval, professor in the Urban Ecology and Animal Communications Lab at the University of Costa Rica in San Jose, raising binoculars in November with his ornithology class for a dawn campus bird walk. In Costa Rica, the Swainson’s thrush does not make its signature song, with its lilting, upward arpeggio. The males only sing this distinctive song during the breeding season up north, to defend territory and probably to attract a mate.
But in their southern range, the birds are not breeding. So, it’s just, “drip, drip, drip,” a steady, sedate, contact call. It, plus the bird’s drab plumage and scuttling ways, looking for insects in the understory, earned the Swainson’s thrush its moniker in Costa Rica, where it’s regarded as a very common, ordinary bird. Not a master songster — and not even as a very smart flier, Sandoval said. The campus frequently is littered with carcasses from Swainson’s colliding with buildings, he noted.
There is a lack of understanding, Sandoval said, of the lives of migratory birds, and the fragile connections, north and south, that sustain them. These birds need healthy habitat everywhere they live — where they breed, where they overwinter and in the stopover places in between.
Swainson’s thrushes, for instance, wing thousands of miles to return to the Pacific Northwest to the very same acre where they nested the previous year, guided by stars, landmarks and even magnetic fields.
Swainson’s thrush travel thousands of miles
Matt Betts, an ornithologist and lead principal investigator at the Long Term Ecological Research site at the H.J. Andrews Experimental Forest, has had the experience, Betts said, of banding a migratory bird at the Andrews and picking up the same bird in the same place, a year later.
Betts is part of a team of scientists studying how habitats in the Pacific Northwest can help support migratory species at this end of their range.
A cooling refuge
At the Andrews, the old-growth forests provide refuge for birds in a warming world, the scientists found in a 2022 paper. Older forests can help slow the effects of climate warming on some breeding bird populations, by providing just a bit of insurance, in the form of more food and a greater variety of it, and places to escape the heat, the scientists learned.
Their findings were devised by placing tracking devices on migratory birds and temperature loggers at various heights of the canopy, so they could see where the birds went as temperatures climbed. Turns out, they went where we would: into the cool, shady, big, old trees.
The paper illuminates solutions to help preserve bird biodiversity. Retaining old-growth forests and managing second-growth to have greater complexity could help blunt species’ declines, the scientists found.
Yet in the Pacific Northwest, clear-cutting of forests limits the availability of the microclimate refuge provided by older forests. Heavy cutting is the reality in the Western United States and elsewhere, where old and natural forests are cut for lumber and replanted as plantations.
Even if forest cover overall does not decline — and even increases — the type of forest that remains matters, scientists found in a 2022 paper. Simplified, younger forest is not equivalent habitat. Older forests are more complex, both in terms of the number of tree species there, and the structural variety of the stands, with old trees, young trees, open areas, dead and downed wood, and a natural understory of herbs, grasses, berries, ferns and more.
A complex natural forest is full of places to nest and roost. There is a lot of food in the insects and berries and seeds found in a variety of plants, dead and downed wood, and canopy. Birds want and need all of those things.
So in degraded areas, one of the best boosts for birds is to bring back diverse, natural forests.
Don’t just plant trees, grow them
In Costa Rica, at environmental nonprofit Finca Cantaros, Executive Director Lilly Briggs knows well that the Swainson’s thrush we think of as ours also are theirs. The research station at Finca Cantaros near San Vito de Coto Bros, at the far southern end of Costa Rica, is pass-through territory for Swainson’s thrush heading north and south. Birds tagged with radio transmitters have been detected on the Motus Wildlife Tracking System station at Finca Cantaros and in B.C., in a tracking program led by Birds Canada.
Radio telemetry has in the past 20 years transformed the understanding of migratory birds, noted Tim Billo, a lecturer in the College of the Environment at the University of Washington. With small transmitters that send a signal picked up on radio receivers, researchers have begun to sketch in the incredible travels of the so-called ordinary birds in our midst.
Many species well known in Washington on the east and west slopes of the Cascades, from rufous hummingbirds to hermit warblers, western tanagers, Townsend’s warblers, orange-crowned warblers, gray catbirds, yellow-breasted chats and many more, travel long distances from their summer forest breeding grounds in Washington to overwinter in Mexico, Central America and South America, Billo noted.
“Most people have no idea about the great distances some of our smallest and even largest and most conspicuous birds travel,” Billo wrote in an email. “And they have little idea about where they are going and the importance of habitat conservation in those areas.”
Betts is astounded by the feat, for instance, of the rufous hummingbird: “It weighs less than a nickel, and tops out at 3 inches in length, and it is one of the longest-distance migrants,” Betts said. Rufous hummingbirds travel between Alaska and Mexico every year, a distance of about 3,900 miles.
It was a bird tagged in Costa Rica that showed up at a Birds Canada tracking station that got Briggs, originally from Vancouver Island, B.C., thinking. Why not restore some of the landscape in San Vito de Coto Brus cleared for agriculture in the 1950s and replant it to forest, for the birds transiting two places she knew and loved?
When a former farm came up for sale in San Vito in 2019, the dream became a reality. Briggs and her husband, David, have since been joining with local community members to replant a forest for Swainson’s thrush and other migratory birds, that need these places to stop over on their long journeys.
Volunteers have helped plant the forest growing now on what in 2019 was cattle pasture. They also take care of it, to keep it thriving. “A lot of people say plant trees. You also have to grow them,” Briggs said.
From girls to grandmothers
On a forest walk at Finca Cantaros in November, women of all ages hiked through a forest amid the soft music of yellow-throated toucans, as morning mist wound through the canopy. The women were from the local village of San Vito, and this was a weekly outing, sponsored by Finca Cantaros.
The hikers hushed with wonder as they spotted an owl in one of the trees. Its silent, wild presence was something they might not have noticed before this program, called Women Committed to the Earth. After the walk, they shared snacks and stories and made art together. Some bring their children, to make it a family affair.
The idea is to not only grow a forest, but a sense among the volunteers of themselves as conservationists, Briggs said. That, and the bond between these local women, their children and this place, is what ultimately will protect the forest, and the birds that rely on it, into the future, Briggs said. Because people take care of what they care about.
“You have to think outside the box,” Briggs said. “What might not look like environmental education absolutely is.”
This story was supported with a fellowship in Costa Rica from the International Center for Journalists and in-country logistical support by Punta y Aparte.
