Southwestern Willow Flycatcher
Copyright by Rick Fridell
Empidonax traillii extimus
NatureServe conservation status
Global (G-rank): G5T2
State (S-rank): S1
Utah Wildlife Action Plan status
- SGCN
External links
Species range
The willow flycatcher ranges across the eastern US to the Pacific northwest and Rocky Mountain region (Sedgewick 2000). The southwestern subspecies breeds in scattered riparian corridors in desert Arizona, New Mexico, southern California, Nevada, Utah, and Colorado. In Utah, this subspecies is limited to the Virgin and San Juan Rivers in the extreme south. It is a migratory species, wintering in rainforests of Mexico, Central America, and northern South America.
Habitat
Nesting sites are in dense riparian vegetation. Typical nesting sites are in dense stands of willows (Salix sp.) with cottonwood (Populus sp.) gallery forest overstory. In some areas, nonnative salt cedar (Tamarix sp.) and Russian olive (Elaeagnus angustifolia) trees are interspersed with native willows, and rarely nests occur in dense stands of these species (McDonald et al. 1997).
Ecology
Willow flycatchers are found in shrubby, wet areas, often along streams and canyon bottoms (Sedgwick 2000). The southwestern subspecies breeds in riparian corridors from nearly sea level to 8,500 ft (Durst et al. 2008), occupying dense tree and shrub patches near water (Sogge et al. 2010). They primarily nest in areas with willows or tamarisk (Federal Register 2013). During migration, they use various riparian habitats, including those with exotic plants (Federal Register 2013). Their diet is mainly insects, supplemented with berries.
Threats or limiting factors
Southwestern willow flycatchers are threatened by damming, urbanization, drought, habitat fragmentation, and invasive plants/insects. Water exploitation and groundwater pumping degrade their river and stream habitats (Johnson et al. 1999). Unregulated livestock grazing harms willow habitats and nests (Sedgewick 2000), as does recreational use.
Invasive tamarisk impacts water resources; in 2007, 4% of flycatcher territories were tamarisk-dominated (Durst et al. 2008). Tamarisk-eating beetles reduced habitat by 94% along the Virgin River (2010-2015), increasing exposure to temperature extremes and predation due to defoliation (Hatten 2016).
Taxonomy
The species to which this subspecies belongs was formerly known as Traill's flycatcher, which included both the species now known as the willow flycatcher (EMPIDONAX TRAILLII) and the species now known as the alder flycatcher (EMPIDONAX ALNORUM). Behle (1985) commented: "Few species have had such a confused nomenclatural history with so many differences of opinion among systematists as to the validity of several proposed races as the Willow or Traill's Flycatcher."
Behle (1985) called attention to the fact that earlier Utah reports (e.g., Behle 1943, Woodbury and Russell 1945) assigned examples of the southwestern subspecies (EXTIMUS) to the subspecies BREWSTERI.