The willow flycatcher (Empidonax traillii) is a small insect-eating bird that breeds in willow thickets and other shrubby wetlands across much of North America. There are four recognized subspecies of willow flycatcher, one of which – the southwestern willow flycatcher (E. t. extimus) – is endangered in California and elsewhere in its range.
Overview of the Willow Flycatcher
The willow flycatcher is a migratory bird that winters in Mexico, Central America, and northern South America before returning to breed across the United States and southern Canada. They build cup-shaped nests in dense shrubs and lay 3-4 eggs. Willow flycatchers feed on flying insects that they capture during short flights from perches on branches. They are brownish-olive above and pale yellowish below.
There are four subspecies of willow flycatcher currently recognized by scientists:
- E. t. extimus – southwestern willow flycatcher (endangered)
- E. t. traillii – little willow flycatcher
- E. t. brewsteri – Brewster’s willow flycatcher
- E. t. adastus – northern willow flycatcher
The southwestern willow flycatcher (E. t. extimus) breeds in dense riparian habitats along rivers and streams in the southwestern United States. The southernmost breeding populations of this subspecies occur in southern California.
Conservation Status of Southwestern Willow Flycatcher
The southwestern willow flycatcher was listed as endangered under the federal Endangered Species Act in 1995. It is also listed as endangered by the state of California, where it is estimated that less than 300 breeding territories remain. Major threats to this subspecies include:
- Loss and degradation of riparian breeding habitat
- Reduced river flows in some areas due to water diversions and dams
- Increased flooding in some areas that damages nests
- Brood parasitism by brown-headed cowbirds
Critical habitat has been designated for the southwestern willow flycatcher along portions of rivers in southern California and other southwestern states. Recovery efforts focus on protecting and restoring riparian areas, controlling cowbirds, and mimicking natural river flows.
Distribution in California
In California, southwestern willow flycatchers breed in dense riparian habitats along the Kern, Santa Ana, and other river systems in southern parts of the state. They typically arrive in late April and depart by early September for their wintering grounds. Population strongholds occur along the South Fork Kern River and Santa Margarita River.
The California Department of Fish and Wildlife estimates there are approximately 275 southwestern willow flycatcher territories located at 28 sites across southern California as of 2020. The biggest populations are found along:
- South Fork Kern River – 95 territories
- Santa Margarita River – 49 territories
- San Luis Rey River – 35 territories
Smaller numbers of breeding flycatchers occur along the Santa Ana, San Diego, Owens, Mojave, and Colorado rivers. Isolated breeding sites also occur at Cuyama and Big Pine Creek. Overall, California supports about 10% of the known global population of this endangered subspecies.
Conservation Efforts
A variety of conservation efforts are underway to protect breeding habitat and support recovery of the southwestern willow flycatcher in California:
- Acquisition and protection of riparian areas along the Kern, Santa Margarita, and other rivers
- Cowbird trapping programs to reduce brood parasitism
- Habitat restoration projects, such as non-native plant removal and native plantings
- Modifications to dam operations to mimic natural river flows
- Monitoring programs to track population trends
Proposed critical habitat was designated by the U.S. Fish and Wildlife Service in 2021 along portions of the Santa Ana River and its tributaries. Ongoing threats include habitat destruction, overgrazing, invasive plants, wildfires, and climate change impacts like drought.
Outlook for the Species
Despite conservation efforts, southwestern willow flycatcher populations remain small and fragmented across California. The species is still vulnerable to extinction and requires ongoing protection and habitat restoration to recover. Maintaining adequate river flows and controlling cowbirds are key management actions needed to support breeding flycatchers. With concerted conservation efforts, there is hope that populations can be stabilized and increased to secure the future of this endangered songbird.
Conclusion
The southwestern willow flycatcher is endangered in California due to substantial population declines and ongoing threats to its riparian habitat. About 275 breeding territories remain in the state, with strongholds along the Kern and Santa Margarita rivers. Extensive conservation efforts, including habitat protection and cowbird control, are underway but populations remain fragile. Ensuring adequate river flows and restoring riparian areas are critical for the recovery of this sensitive songbird in southern California.