A South American bird spotted in Boston last week shows how migrating birds can lose their way.

Jennifer Cutraro

It’s getting close to peak migration season for the millions of birds returning north after a winter in warmer locales. But the fork-tailed flycatcher–a bird that breeds in southern South America and spends its winters in north-coastal Brazil and the Caribbean–has no business to speak of in New England. So Boston-area birders went atwitter last week when one took up temporary residence at Chandler Pond in Brighton, MA.

Bird enthusiasts spotted this fork-tailed flycatcher last week in Brighton. It’s supposed to be in the Caribbean. (Credit: Wayne Petersen, Mass Audubon)

Like our robins and orioles, fork-tailed flycatchers migrate with the seasons. They fly north from South America to the tropics at this time of year—fall in the southern hemisphere. But their navigation systems don’t always get them to where they need to be.

There have been a few fork-tailed flycatcher sightings in the Boston area in the past hundred years, though never one this early in the spring, says Trevor Lloyd Evans, an avian conservation scientist at the Manomet Center for Conservation Sciences in Plymouth, MA.

It’s not unusual to find birds that have ended up in the wrong place during their migration. To make their journey easier, migrating birds try to take advantage of prevailing winds to help carry them to their destination, says Wayne Petersen, director of the Massachusetts Important Bird Areas program at Mass Audubon in Lincoln, MA. “It’s like jumping on an escalator,” he says. “They time it for getting a good tailwind. But that might have gotten this one into trouble–it got more of a ride than it had bargained for.”

This particular flycatcher in Brighton will either spend the summer here or re-orient itself and return south, says Peterson. It was lucky that it wound up here in the summer and not the fall. “If [vagrant flycatchers] come here in the fall, that’s bad news,” he says. Fork-tailed flycatchers feed primarily on insects, which all but disappear by winter.

Birds from the southern hemisphere that fly north in the fall likely have a genetic problem that disturbs their internal navigation system, Petersen says. “A leading hypothesis is that they undergo ‘mirror-image disorientation,’ where they migrate the wrong way,” he says.

Fall vagrants also tend to be young, first-season birds that haven’t yet completed a successful migration south, he adds. That lack of experience, coupled with their off-kilter compass, makes it unlikely those birds will make it home.

That’s probably not the case for the Brighton flycatcher, which is clearly an adult, Petersen says. And because it migrated in the right direction–it just went too far–it probably does not have mirror-image disorientation, he says.

“It may well be a veteran at migration, and it probably got caught up in a weather system where it wanted to go and it just kept on traveling.”