Willow Flycatcher: In Praise of Bird Voice

If there is a yardstick of frequency of occurrence for flycatchers in the Botanic Garden, Black Phoebe will stand at the top, being a year-round resident of the garden. Pacific-slope Flycatcher, Olive-sided Flycatcher and Western Wood-pewee (in descending frequency) will perch in the middle; all of them breed in our area from spring to summer, then go south to spend their winter. Occupying the bottom of the yardstick will be Willow Flycatcher (Empidonax traillii), a spring and fall transient, passing through the San Francisco Bay Area on its way to and from breeding ground and wintering ground.

On our regular garden bird surveys for nearly 4 years, we have yet to record a Willow Flycatcher. But I am lucky to have seen it twice in the garden, both times in early September. And both times I was alerted to its presence first by its calls. Thanks to eBird, which faithfully keeps my bird reports on the cloud for free and allows me to access the data any time, I can say for sure that three years ago on September 6 the bird was on a Button Willow (Cephalanthus occidentalis).

When I first saw the bird, I thought it looked like a Pacific-slope Flycatcher. However, the series of sounds coming from the bird were unfamiliar, and unlike any calls made by a Pacific-slope Flycatcher. When I looked closer, I could see that this small flycatcher did not have a large eye-ring, its head did not sport a peaked crown, and it looked gray. These three features contrast with a Pacific-slope Flycatcher’s tear-shaped eye-ring, obvious crown and olive-green back.

Willow Flycatcher on Western Spicebush (Calycanthus occidentalis), September 3, 2018. By Minder Cheng. 

Pacific-slope Flycatcher on Hollyleaf Cherry (Prunus ilicifolia), September 3, 2017. By Minder Cheng.

The genus Empidonax is notorious for having many species that are hard to tell apart visually. Field guides tell birders that the surest way to identify them is by their voice. Willow Flycatcher and Pacific-slope Flycatcher are not the toughest pair of Empids to distinguish by sight. But as they flit in trees and shrubs, shrouded by leaves and shadows, we often don’t have unobstructed views of them, so their sounds are indeed the best clues.

After encountering the first Willow Flycatcher in the garden, I went home and clicked through recordings at xeno-canto for the best match of what I had heard in the garden. I chose one but felt dissatisfied. One reason is that what I heard were calls, not songs. Songbirds use a variety of communicative calls, which are often quite different from their characteristic songs that are usually delivered by males to court and establish territories. It takes a bird-watcher more effort to learn and recognize bird calls than songs. It’s no surprise that many calls have been overlooked and not recorded.

The two Willow Flycatchers I saw this year on September 3rd in the garden also called, but their sounds were different from that last one from three years ago. As they flew into Western Spicebush (Calycanthus occidentalis) growing on the bank of Wildcat Creek, they made several single notes. To my ear, they sounded like quick whistles, not as fluty as those of Swainson’s Thrush, but thinner, more crisp, and rising in pitch. This time I found the exact match on the website of Nathan Pieplow’s Peterson Field Guide to Bird Sounds of Eastern North America (2017). To listen to Willow Flycatchers that visited our garden, go to “pip” call taped in California. The first 4 notes in “whit” call, also of California, are similar, too. The location is crucial. Pips and whits from other areas sound distinctly different. (Willow Flycatcher has its range over the whole North America, and despite the Eastern focus of the book, the author has generously uploaded songs and calls recorded in many places.)

Speaking of the importance of flycatcher voice, I will never forget a lesson from Denise Wight, instructor of Birding by Ear class sponsored by Golden Gate Audubon. On a spring field trip to Sunol Regional Wilderness, we came upon a Hammond’s Flycatcher. She tilted her head and purposefully looked away.  She said, “Listen!” All the students’ eager eyes glued to their binoculars became unhinged—no looking, and only listening? As Donald Kroodsma writes in Listening to a Continent Sing: Birdsong by Bicycle from the Atlantic to the Pacific (2016), “Seeing birds is highly overrated….No, for me it is their voices that are so special….So, who cares what they look like?”