Rare Southwestern Willow Flycatcher Banded by USGS Spotted on Nicaragua Wintering Grounds

USGS ecologist Barbara Kus got some very exciting news last week—a Southwestern Willow Flycatcher that her team had banded in San Diego in July 2017 was spotted on its wintering grounds in Nicaragua, thanks to the colorful band on its leg. The bird was spotted by a crew from the non-profit Southern Sierra Research Station and Paso Pacifico, led by ecologist Mary Whitfield.

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"It's the true needle in the haystack!” said Kus. Only sixteen birds have these colorful bands, so spotting even one banded bird amid a population of more than 3 million Willow Flycatchers is exceedingly rare.

The Southwestern Willow Flycatcher (Empidonax traillii extimus), a federally endangered subspecies of the more abundant Willow Flycatcher, is a small migratory bird that breeds along rivers in the southwestern US and winters amid other subspecies in Mexico, Central America, and northern South America. The Southwestern Willow Flycatcher is endangered primarily due to habitat loss.

Understanding the threats facing birds on both the breeding and wintering grounds is an essential part of species recovery, but very little is known about where specific breeding populations spend the winter. The Southwestern Willow Flycatcher is too small to attach transmitters and other modern devices to track migratory routes, so scientists rely on re-sighting individually color banded birds to identify their breeding and wintering grounds. Studies on museum specimens by the San Diego Natural History Museum and genetic studies by Eben Paxton of USGS and from UCLA’s Bird Genoscape Project have helped researchers identify countries where the different Willow Flycatcher subspecies spend the winter, allowing researchers studying for the Southwestern Willow Flycatcher to narrow their search area. But getting more precise information currently requires spotting those needle-in-a-haystack birds.

The bird that was spotted in Nicaragua was originally banded as a nestling by USGS biologist Scarlett Howell on the upper San Luis Rey River in July 2017. In 2019, Howell recaptured the bird on her breeding territory a short distance upstream and gave the bird a more colorful band that is easier to spot. This colorful band is what sharp-eyed observers spotted on the wintering grounds last week. They recaptured the bird to confirm its identity.

“Slowly but surely, we're connecting the dots between the breeding and wintering grounds for our local Southwestern Willow Flycatcher populations!” said Kus.

The sighting of this color banded bird provides the first evidence that connects San Diego County populations to a wintering site in Nicaragua, information that will benefit the species at both ends of its geographic range and inform conservation efforts.

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