Better Know a Bird: the Remarkable Migration of the Secretive Sora
Standing in a high-quality marsh during the peak of migration, you might be surrounded by hundreds of Soras—but you could leave without encountering a single one. As Soras move between their breeding grounds in the north-central U.S. and Canada to their wintering range along southern shores, Mexico, and beyond, they traverse nearly the entire continent. But because they hide in wetland reeds to survive, Soras are rarely spotted.
Greg Kearns, park naturalist at Patuxent River Park in Maryland, has seen his fair share of Soras and then some. In the past 35 years, at part of their effort called Project Sora, he and his team have tagged more than 6,000 of these elusive birds in Patuxent’s marshlands and wild rice beds. “Their secretive nature, I think, is what protects them and intrigues me,” Kearns says. “Little was known about their migration routes, the chronology of it, and habitat use.” But now, scientists like Kearns are uncovering the secrets of these birds, including their fantastic migrations.
Soras are long-distance migrants, but at a first glance, they hardly look the part. Stout and stubby-winged, Soras belong to the rail family, a group of marsh-dwelling birds that largely prefer walking to flight. When they do take to the air, Soras flap with dangling legs in an awkward, labored movement that only lasts for a short distance. But that changes during migration seasons, when Soras wing their way to far-off destinations and back. Some even travel to South America, as far as Ecuador or Peru—the longest migration of any North American rail.
Patuxent River Park acts as a pit stop for Soras on their journeys, though a few do winter there. Kearns uses recorded Sora calls to lure the birds into walk-in traps, then he affixes tiny radio trackers onto their backs. Using the Motus Wildlife Tracking System, he gets data back about where these birds go and how quickly they get there. This spring, for example, he’s traced birds’ paths north from Patuxent to breeding grounds in the Great Lakes region. One of the most notable migrations recorded by Project Sora saw one bird fly nonstop from Maryland to the Bahamas in less than 20 hours. Another, which the researchers named Pea, made it from Patuxent River Park to North Carolina’s Pea Island National Wildlife Refuge in under 5 hours—a time that would beat a lot of motorists driving between the two places.
What’s more, migrating Soras are constantly flapping. Hawks, on the other hand, glide to conserve energy, and many smaller birds such as sparrows and finches break up their flaps with short bobs in midair (called bounding flight). To quantify what a Sora’s flap-flight really means, Kearns took a slow-motion video of one on its migratory trip. By counting how many flaps it did in 10 seconds and multiplying that out across the bird’s nine-hour journey to North Carolina, he determined the bird flapped about 285,000 times to get there. To reach the Bahamas, Kearns estimates a Sora would take something like 600,000 flaps—or more, if it continues south through the Caribbean. “It’s mind-boggling,” he says.
So how does a ground-loving wading bird accomplish these aerial feats? For one, they get a bit of help. When timing their migrations, Soras appear to take weather into account, says Auriel Fournier, assistant research scientist with the Illinois Natural History Survey. During fall migration in Missouri, she’s seen masses of them arrive in an area just after a cold front. “After a front like that, there’s often pretty steady winds that follow,” she says. “In a lot of cases, they’re hopping on those winds after and following those south.” By using this strategy, Soras raise their speed from about 30 to 35 miles per hour unaided to 45 miles per hour on average, to—on an unusually strong wind—more than 75 miles per hour, according to Kearns’ observations.
But riding the wind is a double-edged sword—on the flip side, Soras are at its mercy, vulnerable to a strong gust in the wrong direction. Some, Kearns speculates, likely die over the ocean. But in extreme cases, Soras blown off-course have traversed the Atlantic, ending up in the Canary Islands off the coast of Northwest Africa, the United Kingdom, the Azores, Portugal, and even Norway.
To fuel their impressive migration bursts, Soras need lots of time for refueling along their journeys. Migrating warblers typically rest for a couple days at a time, but Fournier says Soras may rest at a site for upwards of a month, where they fatten up by eating lots of carbs. They shift their diet from protein-rich invertebrates to seeds from smartweeds, sedges, grasses, or wild rice. “They’re doing a little couch potato routine out there on the marsh,” Kearns says. The Soras steadily gain mass, and as departure nears, they put on weight even faster. Birds go from weighing 50 to 60 grams to 80 or 90 grams, Kearns says. Then, with their fat stored up, the Soras begin to leave with the right winds and clear skies about an hour after sunset.
Making such an extreme migration takes a toll on Soras’ population, and the birds’ large clutch size of 10-12 eggs helps replenish their numbers. But other threats remain: In the past, hunting decimated the Sora. Now, with hunting scaled back, climate change and human development are causing habitat destruction that complicates Soras’ journeys. In Illinois, where Fournier works, more than 80 percent of the state’s wetlands have already been lost, and it’s a similar story in other states. “That makes their lives more challenging during migration, which can already be a dicey time of year,” Fournier says.
But when they do land in high-quality habitat, such as the wild rice ecosystem at Patuxent River Park, year after year, it’s a testament to the marsh’s importance, Kearns says. These are the places that will ensure Soras can continue to successfully navigate their death-defying migrations in the future. “That’s really what the bottom line is,” Kearns says. “We have to protect these wetlands.”