The fate of the southwestern willow flycatcher is intimately linked to the health of the Grand Canyon.
By Michael Engelhard
It’s not notable for its plumage or song, not venomous or otherwise “bizarre,” not a keystone species or top predator. Few visitors to the Grand Canyon notice its presence, and even fewer would notice its absence. But according to one of its most ardent fans, wildlife biologist Mark Sogge, it’s a symbol of what we are doing to our river corridors.
Given the battery of threats it faces, the endangered southwestern willow flycatcher’s continued presence could be considered a miracle. This unassuming “snowbird” visits the Southwest in May, June, and July to mate and raise its broods along lush river corridors. The journey from its wintering grounds in Latin America takes an epic toll: Research shows that of all the flycatchers that die every year, 64 percent do so during migration. Snakes and Cooper’s hawks further decimate its numbers by preying on hatchlings. Brown-headed cowbirds smuggle eggs into flycatcher nests, where flycatcher chicks have to compete with the hulking, alien offspring. Overgrazing, pollution, urbanization, agricultural stream diversions, and other development here and south of the border have reduced Empidonax traillii extimus to fewer than one thousand breeding pairs.
Now, global warming threatens to push the greenish-gray songster over the brink. “Current habitats may dry up,” says Rosa Palarino, a Grand Canyon National Park biologist. As the climate changes, so, too, may the food base and nesting opportunities for flycatchers. The bird’s flexibility, however, is a silver lining of hope—it can rebound quickly when conditions improve.
Though not a water bird per se, this finch-sized subspecies is irrevocably bound to the element. It breeds in broad, dense, young willow and tamarisk stands, forages among marsh plants like cattails, and migrates along the lifelines of desert streams. With wildly fluctuating, dam-regulated water levels and a declining flycatcher population, the Colorado River in Grand Canyon National Park is a perfect proving ground for flycatcher conservation.
To establish the number of breeding flycatchers, the park is expanding its sound-monitoring program this year, covering the entire canyon from Lee’s Ferry to Lake Mead. Armed with speakers, sophisticated microphones, and recorders, Palarino and fellow researchers will stalk the reclusive bird in the bushes, broadcasting taped flycatcher vocalizations, which elicit a response from any male eager to announce territorial claims. They’ll follow up with a visual identification, to detect breeding activity and nest sites.
Not surprisingly, Lake Mead’s fickle waters effect dramatic changes in willow flycatcher habitat in the lower reaches of the Colorado River. Between 2000 and 2008, when the reservoir dropped more than 100 feet, vegetation crucial for nesting and foraging was killed off. Throughout the past decade’s drought, lower water levels at many nests thinned the surrounding canopy as drought-resistant plants replaced moisture-loving ones, much to the bird’s disadvantage.
The southwestern willow flycatcher’s distribution only magnifies conservation challenges. Sites with small populations (five or fewer breeding pairs) are vulnerable to threats like brush fires, which flare up more frequently with prolonged droughts. But exactly how the birds choose their habitat is still poorly understood. Some scientists believe that isolated flycatcher enclaves may serve as “genetic reservoirs” from which new areas are populated, and therefore advise land managers not to abandon smaller flycatcher populations—like the Grand Canyon’s—in favor of larger populations (20 or more breeding pairs) found along New Mexico’s Gila and Rio Grande and Arizona’s San Pedro River. Protected pockets of flycatcher habitat also need to be linked by stopover habitats that play a key role during migration and help birds to reach their nesting grounds.
An additional twist comes in the guise of the tamarisk, an invasive, water-guzzling shrub that crowds out native vegetation. Most parks manage tamarisk aggressively; on state lands, biologists have released beetles that feed on and kill the green invaders. But as the larvae munch their way toward the Grand Canyon, they create a temporary vacuum in the flycatcher’s nesting canopy. And that recent progression is a pressing concern, according to R.V. Ward, Grand Canyon wildlife program manager. To sustain nesting habitat for flycatchers, native plants need a chance to re-colonize riverbanks. In the future, the Park Service may have to reseed and replant willows, cattails, and bulrushes in the absence of tamarisk to prevent soils from washing away.
Archaeologists believe that early inhabitants of the Grand Canyon were forced to leave when climate change and deforestation led to barren springs, barren soils, and erosion. Now, hundreds of years later, some of those same factors could contribute to the demise of the southwestern willow flycatcher. But with concerted efforts to preserve habitats and tackle greenhouse-gas emissions, its birdsong might echo through the canyon for years to come.