Southwestern Willow Flycatchers, Yellow-billed Cuckoos, and the Las Vegas Wash

By Morrigan DeVito

Artwork by Myranda Bair

The cottonwoods and willows along the Las Vegas Wash shelter many migratory bird species throughout the year. This summer, Southwestern Willow Flycatchers and Yellow-billed Cuckoos, which are neotropical migrants who journey from wintering grounds in South and Central America to breeding grounds in North America, will pass through Southern NV. Both birds are listed as federally threatened and endangered in the U.S and have become focal points for riparian conservation in Southern NV. Can the Las Vegas Wash help them recover? 

Southwestern Willow Flycatcher

In the passerine family along with other flycatchers like the Black Phoebe and Vermilion Flycatcher, the Southwestern Willow Flycatcher (SWFL) is a dainty, white-throated bird that breeds in late-April throughout the American Southwest after wintering in Central and South America. The males arrive first to stake out the best territory in habitat with native willows like Gooding’s, seep, and coyote willow. They prefer to raise their young in trees that are well saturated with water, perhaps to deter predators or to keep the nestlings cool in the desert heat. When they’re not defending their territory or raising young, SWFL pass the time darting through the air to catch and eat insects like flies, ants, bees, dragonflies, mosquitoes, and more. 

The SWFL is the only willow flycatcher to breed in NV, making them a high priority species in the Nevada Department of Wildlife’s 2013 Wildlife Action Plan. The biggest threat to their breeding success is habitat loss and alteration of the Colorado River and other rivers in the region, since they are a sensitive species that depends on dense riparian vegetation during breeding season. Another threat to their success are Brown-headed Cowbirds, which parasitize their nests by dumping their eggs next to SWFL eggs or even destroying the willow flycatcher’s eggs after leaving their own. After all the eggs hatch, the Brown-headed Cowbird, bigger and stronger than its “siblings”, outcompetes them for food and the SWFL unintentionally raises the cowbird instead. 

Western Yellow-billed Cuckoo

The western Yellow-billed Cuckoo (YBCU) is another neotropical migrant that is declining, with fewer than 500 pairs breeding in the Western U.S. They are listed as critically imperiled in NV, endangered in CA, and threatened in UT, which reflects the different levels of management done for YBCU in different states. Like the SWFL, their biggest threat is loss and alteration of riparian habitat along the Colorado River. 

Made for the cottonwood stands where they sit very still in the canopy, the underside of a YBCU’s long tail is mottled like cottonwood bark. They forage for insects in the dense foliage, with a strong appetite for caterpillars. They are often the first to arrive of the summer breeding migrants, arriving in Southern NV by late June. To build their nests made of loose sticks, they need an overstory canopy in dense willow and cottonwood forests near the water. But unlike the SWFL, they do not need trees to be saturated with water and can even nest in mesquite stands that are connected to riparian habitat. 

SWFL and YBCU Conservation in the Las Vegas Wash

Will you encounter a Southwestern Willow Flycatcher or Yellow-billed Cuckoo breeding in Las Vegas on your next birding day? The odds are quite low. According to Debbie van Dooremolen, environmental biologist with the Southern Nevada Water Authority (SNWA), there has been one confirmed case of a SWFL breeding along the Las Vegas Wash, but it was parasitized by cowbirds. However, SWFL are known to breed at Pahranagat Valley National Wildlife Refuge

Only two YBCU nests have been recorded in the entire state of Nevada, one of which was documented in the early 2000s at the Warm Springs Natural Area, an oasis in Moapa and managed by SNWA.

“YBCU are much rarer in the state than SWFL,” Dooremolen says. “If we have a few detections of YBCU a year at our sites [Las Vegas Wash and Warm Springs Natural Area] we are thrilled.” 

Nonetheless, any activity for SWFL or YBCU is a big milestone and suggests the potential for future breeding along the Las Vegas Wash and elsewhere in Southern NV. The Las Vegas Wash Coordination Committee (LVWCC) has surveyed for Southwestern Willow Flycatchers every summer since 1998 and Yellow-billed Cuckoos every summer since 2013. The monitoring that the LVWCC does helps show the capacity for abundance that this urban river has. Overall, about 300 bird species have been documented along the Wash since 1998, and birders of RRAS experienced with these species have helped the LVWCC census birds throughout the Wash. 

The Las Vegas Wash was established in the 1950s after it became a perennial stream and year-round flow caused erosion and water quality issues. By 1998, the LVWCC was formed to address these issues, working with different agencies like SNWA, City of Las Vegas, City of Henderson, and more. 

Fast-forward to today, and the Las Vegas Wash is managed with weirs to control water flow and annual revegetation projects to remove invasive species and instead plant native willows, cottonwoods, and more. Invasive tamarisk has been the notorious target of removal, and although SWFL will nest in tamarisk, YBCU will avoid vast stands of tamarisk. Because of the collaboration between the LVWCC and its partners, invasive tamarisk along the Las Vegas Wash has been reduced 99% to 15 acres.

SWFL and YBCU, along with countless other animal and plant species, benefit from revegetation projects, even if there have not been a high number of documented nests yet. An abundant wildlife corridor for birds, insects, reptiles, and mammals, The Wash runs through the Las Vegas Valley with trails at Clark County Wetlands Park, the East Las Vegas Wash, Pittman Wash in Henderson, and others. 

To get involved and help take care of the Wash, Dooremolen suggests looking at the LVWCC website to sign up for stewardship events like Wash Green-up, a volunteer planting project to restore native plants along the Wash. You can also look at Warm Spring Natural Area’s website to volunteer at their revegetation projects. 

Although you may not encounter a Southwestern Willow Flycatcher or Yellow-billed Cuckoo in Las Vegas, advocating for their conservation branches beyond just protecting their species. Ensuring that there is high-quality habitat along the Las Vegas Wash with different layers of cottonwoods, willow, mesquites, saltbush, and other native plants has an effect on hundreds of other bird species, from other neotropical migrants to rails, waterfowl, shorebirds, and more. And as the native plants establish themselves and grow taller, the habitat quality will continue to get better. 

“RRAS is vital to my story,” Dooremolen says. “I started with SNWA on the Las Vegas Wash Project Coordination Team as an undergraduate in 2001. The first project I was assigned to was a bird survey that was coordinated by SNWA biologists but conducted by RRAS birders [...] the fantastic members of RRAS that helped [...] got me hooked on bird surveys and I’ve been doing them in some form or another ever since!”