Why some 'lost' birds took a wrong turn - on purpose

In 2009, a group of teenage birders were hiking in the Huachuca Mountains when they heard a bird call that didn’t sound familiar. It echoed through the canyon, soft and flute-like – totally out of place.

One of them pulled out a phone and started scrolling through bird calls. When he played the brown-backed solitaire, it clicked. That was the bird.

But it didn’t make sense. The brown-backed solitaire lives in the mountain forests of Mexico and Central America – not Arizona.

That odd moment kicked off a much bigger question: why do some birds show up way outside their normal range?

These out-of-place birds are known as vagrants. For birdwatchers, they’re an exciting find. But for scientists, they might point to something deeper – how birds adjust, evolve, and sometimes even change their migration routes entirely.

Why do birds get lost?

Birders love a good surprise. When a rare bird shows up in the “wrong” place, word spreads fast. Spotting a vagrant can feel like winning the lottery. But for scientists, it opens up a different line of questions.

Are these birds just confused? Are they evolutionary dead ends? Or are they doing something more important – maybe even paving the way for their species to adapt to new environments?

One ornithologist who’s been chasing those answers is Benjamin Van Doren. That hike in 2009 led to his first scientific paper.

Today, Van Doren is part of a team at the University of Illinois Urbana-Champaign, Cornell Lab of Ornithology, and Point Blue Conservation Science. The researchers are investigating how and why some birds go off-route.

A remote island that catches strays

One place in the U.S. shows up in vagrant bird reports more than almost anywhere else: the Farallon Islands.

Southeast Farallon Island, about 30 miles off the coast of San Francisco, is a rough, remote patch of rock in the Pacific. It’s been a key spot for wildlife research since 1967.

During migration season, the island turns into a surprise landing zone for birds that have strayed far from their usual path.

For this study, researchers focused on six types of American warblers – small, colorful songbirds that had ended up on the island, far from their expected routes.

The team collected feathers from recent vagrants and also pulled museum samples from as far back as the late 1800s.

Feathers reveal origins of lost birds

Inside every feather is a hidden GPS, but not the kind with satellites. Instead, scientists used hydrogen isotopes – specifically a form of hydrogen called deuterium – to trace the birds’ origins.

Water across the world contains slightly different ratios of regular hydrogen and deuterium. When birds eat and drink, their bodies absorb the local water’s unique isotope signature.

The signature gets locked into their feathers when they grow. By analyzing these ratios in the feathers, scientists can match them to specific regions.

The result: all six warbler species came from the western part of their usual breeding range, in Canada’s vast boreal forest. These western populations were also smaller than the more densely populated eastern groups.

“You might hypothesize that any bird has the potential to just go off in a random direction and end up anywhere else, but that’s not what we found,” said Van Doren.

“Another hypothesis is that birds living in more densely populated areas are more likely to become vagrants. Our results didn’t support that idea, either.”

What vagrancy might really mean

In the 1970s, a scientist studying the same island proposed that vagrant birds might be making a simple navigation mistake.

Many songbirds use an internal compass for migration, likely passed down from their parents. If something scrambles that compass – like a small genetic mutation – the bird might head in the exact opposite direction.

So instead of flying southeast in the fall, it flies southwest. That could explain why some East Coast birds end up on the West Coast. This new study supports that idea but doesn’t prove it outright.

Still, there’s something interesting about the fact that these birds came from the western edges of their range. It suggests that vagrancy might not always be a failure. Sometimes, it could be a first step.

“With climate change, places that were previously inhospitable could now be suitable in the winter. Vagrant birds could be the start of populations adapting to changing habitats and might actually be a critical part of the cycle of range expansion in migratory birds,” Van Doren said.

“You could think of these rare birds as possibly the vanguard of population change and geographic distribution change.”

Vagrant birds that aren’t lost

Scientists still don’t know exactly what causes some birds to take off in the wrong direction. If birds inherit their migration path, a tiny mutation could flip that path entirely. That’s one theory. But so far, no one has nailed down a universal answer.

“Vagrants are very hard to study and understand because you never know where or when they’re going to show up. It’s typically very unpredictable,” said Van Doren.

For now, he and his team are pushing the research forward, hoping to build a better understanding of how birds adapt, migrate, and possibly even reinvent their own routes.

“These rare bird occurrences could just be lost birds that are not going to survive,” Van Doren said. “But there is another perspective, that maybe they’re not so ‘lost.’ Maybe they are explorers.”

The full study was published in the journal Ornithology.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–