In the birding world, the look-alike Empidonax flycatchers—affectionately or dejectedly referred to as “empids”—create two non-overlapping groups: those who eagerly rise to the ID challenge (not me) and those who despairingly mutter “empid” and move on (me). But one empid occupies a rarefied spot in San Diego County: the Southwestern Willow Flycatcher.
The Willow Flycatcher species (Empidonax traillii) comprises four subspecies. As the only breeding subspecies in San Diego County, the Southwestern Willow Flycatcher (E. t. extimus) holds a dubious honor as one of Southern California’s rarest birds. (Note that at least one other subspecies passes through during migration—E. t. brewsteri.) The Southwestern Willow Flycatcher breeds here in only two modest-sized colonies and a few dispersed pairs. The larger breeding colony lies along the upper San Luis Rey River, from just below Lake Henshaw to the La Jolla Indian Reservation. The second colony inhabits the Santa Margarita River through Camp Pendleton. Some dispersed pairs breed along the lower San Luis Rey River: near Whelan Lake, a bit north of Guajome Lake, and around Pala. And, given eBird reporting, other pairs likely occur elsewhere in the county, less well documented but scattered in patches of appropriate habitat.
Early in the 20th century, Willow Flycatchers occurred in a variety of riparian areas of San Diego County. The population collapsed in the mid-20th century, as the devastating impacts of Brown-headed Cowbird parasitism, clearing riparian woodland, damming rivers, overgrazing, and urbanization combined to create a Willow Flycatcher death sentence. In all, this subspecies has lost 90-95% of its historical habitat. Current prevalence estimates remain elusive. But during the atlasing efforts for the San Diego County Bird Atlas two decades ago, the population here numbered fewer than 90 pairs, out of only about 200 statewide.
A lanky (well, for an empid—~5.75”), plain, brownish flycatcher, the Willow Flycatcher sports a large bill, a peaked head, and a moderately long tail. It shows a whitish throat and a dingy white chest and belly sometimes slightly tinged with a yellow so understated you probably just imagined it. The lack of a distinctive eye ring can also set it apart from other empids. Extimus differs from brewsteri by its paler upperparts and lack of contrast between its crown and back. (Yeah. Good luck making that distinction.) But really—the best way to separate the various empids lies with their voices. Willow Flycatchers utter a raspy, emphatic “fitz-BEW!” (If distinguishing the nigh-on-indistinguishable empids doesn’t turn you into a rabid student of bird songs and calls, nothing will.)
Willow Flycatchers feed primarily on aerial insects, darting out in short flights to catch them mid-air; these birds also hover to snatch insects from leaves. The flycatcher menu boasts of prey as diverse as flying ants, bees, wasps, gnats, and cicadas.
Males of the local population of E. t. extimus usually arrive in early May, one or two weeks before the females. Historically, willows hosted nearly 90% of these birds’ nests (hence the common name). The female lays a clutch of 3–4 eggs; incubation requires 12–15 days; and the young fledge 14–15 days after hatching. Fledglings stay with the adults another 10 days, honing those tricky aerial-insect food-snatching techniques. Beginning in August, these flycatchers begin to head to their wintering grounds in Mexico and Central and South America.
The genus name, Empidonax, traces its roots to Greek for “gnat master” (empis, “gnat;” anax, “master” or “king”). The members of this flycatcher genus all perform the important community service of insect control—especially those pesky flying insects (which also explains the common name “flycatcher”). The species name, traillii, honors Thomas Stewart Traill, a 19th-century Scottish physician who protested the neglect of the natural history collections of the British Museum and arranged for their relocation to the newly formed Museum of Natural History. Finally, as noted earlier, “willow” refers to the species’ historically preferred nesting site.
Unfortunately, willow habitats have declined dramatically in recent years. In the face of this widespread degradation, a remnant group of Willow Flycatchers below Henshaw Dam fortuitously began to nest in a non-willow substrate—coast live oak. Between 1995 and 2001, more than 70% of nearly 300 documented nests occurred in oak trees, with another 8% in habitats associated with live oak. And more good news—this colony has evidently increased to the point that it is now the largest breeding colony of E. t. extimus in the state. The decline, at least in this area, seems to have stopped and recovery has begun, albeit still too slowly. The bad news, though, is that coast live oaks tend to burn more readily than do other riparian trees, exposing birds nesting in them to enhanced fire danger.
Given so many pressures, the U.S. Fish and Wildlife Service (USFWS) listed the Southwestern Willow Flycatcher as “endangered” under the Endangered Species Act (ESA) in 1995. Unfortunately, the birds’ preferred riparian habitats also make prime real estate for humans. As a result, in 2015, after two decades of attempts to undermine the listing, the pro-development Pacific Legal Foundation petitioned to remove this subspecies’ ESA protections based primarily on a rather sketchy concept put forth in a single study: The subspecies was not genetically unique. Since other subspecies of Willow Flycatchers thrive elsewhere in the U.S., such a reclassification would render special protections unnecessary. Among other problems, though, the lead author of this study had admitted to taking money from property developers for similar research in the past, casting doubt on the author’s objectivity. But more importantly, most avian experts argued that this one study wasn’t nearly enough to overturn decades of research to the contrary.
In 2016, the USFWS had rejected a similar petition by the same group to strip protections from the tiny coastal California Gnatcatcher. In December, 2017, the USFWS once again found in favor of a small bird: The agency upheld the Southwestern Willow Flycatcher as a valid subspecies and its protections remain. In effect, this subspecies had been targeted for removal from ESA oversight not because its numbers had rebounded but because it stood in the way of property development. Even in these times of increasing attacks on research, important back-to-back victories of science over special interests have emerged. At least so far. Not surprisingly, the petitioners have now taken the USFWS to court. And Texas rancher Susan Combs, surreptitiously appointed last month to oversee the USFWS, boasts a long history of hostility toward endangered species and the protections their status engenders. Stay tuned, stay engaged, and don’t let your guard down.