Basic Information
Common Name: Southwestern Willow Flycatcher
Scientific Name: Empidonax traillii extimus
Species Code: EMPTRA
Management Category: SL (species at risk of loss)
Occurrence Map
Table of Occurrences

Species Information

MSP Species Background

Goals and Objectives

Goal: Protect, enhance, and restore southwestern willow flycatcher occupied and historically occupied habitat to create resilient, self-sustaining populations that provide for persistence over the long-term (>100 years).

regional NFO 2017, 2018, 2019 SL

Management units: 1, 4, 6, 8, 9, 10, 11

In 2017-2019, continue the 5-year breeding bird study begun by USGS in 2015 of southwestern willow flycatcher in the San Luis Rey River and other drainages to determine the status in the MSPA and impacts to riparian habitat from SHB/Fusarium complex and other threats. Prepare site-specific management recommendations based on survey results.

Action Statement Action status Projects
RES-1 Submit monitoring data and management recommendations to MSP web portal In progress
Criteria Deadline year
Southwestern Willow Flycatcher Surveys and Reports Completed by 2020 2021
regional NFO 2020, 2021 SL

Management units: 1, 4, 6, 8, 9, 10, 11

In 2020-2021, prepare a management plan for southwestern willow flycatcher based on survey recommendations and that includes provisions for reducing potential impacts of SHB/Fusarium infestation in occupied or potential habitat. Incorporate SHB/Fusarium monitoring results into the management plan, particularly along the San Luis Rey River.

Action Statement Action status Projects
PRP-1 Prioritize management actions, focusing on reducing threats and expanding occurrences in areas most likely to remain viable over the long-term in the context of future land development. Available for implementation
PRP-2 Develop an implementation plan for southwestern willow flyycatcher that prioritizes management actions for the next five years. Available for implementation
PRP-3 Submit management plan to MSP web portal Available for implementation
Criteria Deadline year
Management Plan for Southwestern Willow Flycatcher prepared by end 2021 2021
regional NFO 2021 SL

Management units: 1, 4, 6, 8, 9, 10, 11

Beginning in 2021, implement the highest priority management actions for southwestern willow flycatcher on Conserved Lands.

Action Statement Action status Projects
IMP-1 Management actions to be determined by the management plan. waiting for precedent action
IMP-2 Submit project data and management actions to MSP web portal waiting for precedent action
Criteria Deadline year
Management actions initiated for Southwestern Willow Flycatcher 2021
regional NFO 2021 SL

Management units: 1, 4, 6, 8, 9, 10, 11

Beginning in 2021, monitor the effectiveness of management actions implemented for southwestern willow flycatcher on Conserved Lands

Action Statement Action status Projects
IMP-1 Submit monitoring data and reports to MSP web portal waiting for precedent action
Criteria Deadline year
Monitoring completed and data and report submitting within 1 year of management actions being completed. 2021
Southwestern Willow Flycatcher Status and Demography
This is a planned 5-Year study. USGS will conduct a 2-phased investigation to: 1) document the abundance and distribution of flycatchers in San Diego County; and 2) collect demographic data that will permit an assessment of the San Luis Rey River population within the larger contexts of MSPA and the state. During phase 1, drainage-wide surveys were conducted from Lake Henshaw downstream to College Boulevard in Oceanside between May and August 2015. These surveys were repeated in 2016, focused on sites outside of the San Luis Rey drainage that have historically supported resident southwestern willow flycatchers, including the Otay, Sweetwater, and San Diego Rivers, Santa Ysabel Creek, and Agua Hedionda. Phase 2 demographic data collection through monitoring started in 2016 and continued through 2017. In 2018, the focus is on monitoring flycatcher pairs in the upper San Luis Rey River study area, and banding and re-sighting color-banded flycatchers. Surveys will also be conducted outside the San Luis Rey drainage.
SR 94 Wildlife Infrastructure Plan
Proposed road improvements to SR 94 provide an opportunity to mitigate the potential barrier effects of the highway. This project identifies where improvements to existing infrastructure on SR-94 could improve connectivity across the South County preserves, using Best Management Practices from the scientific literature; recommends wildlife movement monitoring to identify where new crossings are needed; and identifies where additional conservation would enhance the integrity of South County linkages. The review prioritizes infrastructure improvements of 35 existing undercrossings inspected by wildlife experts in the field along 14.6 miles of SR-94 where the highway bisects conserved lands. The majority of the recommendations for infrastructure improvement focus on increasing the diameter, and thus the openness ratio (cross-sectional area divided by length), of the undercrossing itself, removing vegetation and debris blocking the undercrossing, restoring habitat in the approach to the undercrossing, and installing fencing to both (1) keep animals off the highway and (2) funnel wildlife to the undercrossings.
File name Lead Author Year Type
1997 Sensitive Species Survey Results for Pine Creek and Hauser Canyon Wilderness Areas, Descanso Ranger District, Cleveland National Forest, San Diego County, California. Wells, Jeffery M.; Turnbull, Jennifer 1998 report
2008 Species Survey Annual Report Famolaro, Pete 2009 report
Abundance and distribution of Southwestern Willow Flycatchers in San Diego County Howell, Scarlett L.; Kus, Barbara 2022 powerpoint presentation
Biological Monitoring Report for the Tijuana River Valley Regional Park (Monitoring Year 2009) 2010 report
County of San Diego MSCP Monitoring Summary Report January 1998 - June 2007 County of San Diego 2007 report
Demography of Southwestern Willow Flycatchers in San Diego County, California Kus, Barbara; Howell, Scarlett L.; Mendia, Shannon 2022 powerpoint presentation
Distribution and Abundance of Southwestern Willow Flycatchers (Empidonax traillii extimus) on the Upper San Luis Rey River, San Diego County, California—2021 Data Summary Howell, Scarlett L.; Kus, Barbara 2022 report
Distribution and Breeding Activities of the Least Bell's Vireo and Southwestern Willow Flycatcher at the San Luis Rey River, San Diego County, California Rourke, James W.; Kus, Barbara 2007 report
Distribution and Demography of Southwestern Willow Flycatchers in San Diego County, 2015–19 Howell, Scarlett L.; Kus, Barbara; Mendia, Shannon 2022 report
Distribution, Abundance, and Breeding Activities of the Southwestern Willow Flycatcher at Marine C Ferree, Kimberly; Kus, Barbara 2003 report
Distribution, Abundance, and Breeding Activities of the Southwestern Willow Flycatcher at Marine C Kenwood, Kerry E.; Kus, Barbara 2003 report
Distribution, Abundance, and Breeding Activities of the Southwestern Willow Flycatcher at Marine Co Kus, Barbara 2001 report
Distribution, Abundance, and Breeding Activities of the Southwestern Willow Flycatcher at Marine Corps Base Camp Pendleton, California Rourke, James W.; Kus, Barbara; Howell, Scarlett L. 2008 report
Distribution, Abundance, and Breeding Activities of the Southwestern Willow Flycatcher at Marine Corps Base Camp Pendleton, California Rourke, James W.; Kus, Barbara; Howell, Scarlett L. 2008 report
FINAL Baseline Biodiversity Survey for the San Luis Rey River Park 2011 report
Least Bell's Vireos and Southwestern Willow Flycatchers at the San Luis Rey Flood Risk Management Pr Ferree, Kimberly; Kus, Barbara 2008 report
Least Bell's Vireos and Southwestern Willow Flycatchers at the San Luis Rey River Flood Control Proj Kus, Barbara; Ferree, Kimberly 2008 report
Quarry Creek Preserve Management Plan 2011 report
Recording - January 2022 SDMMP Management and Monitoring Coordination Meeting Kus, Barbara; Howell, Scarlett L. 2022 recording
Southwestern Willow Flycatcher Breeding Site and Territory Summary - 2006 Kus, Barbara; Durst, Scott L.; Sogge, Mark K.; Stump, Shay D.; Williams, Sartor O.; Sferra, Susan J. 2007 report
Surveys for the Least Bell's Vireo and Southwestern Willow Flycatcher at the San Luis Rey River Kus, Barbara; Peterson, Bonnie L.; Wellik, Mike J. 2002 report

Current Distribution Rangewide

Breeding range: southern California, Arizona, New Mexico, southern Nevada and Utah, western Texas, southwestern Colorado, and possibly northern portions of the Mexican states of Baja California, Sonora and Chihuahua [1]. Winters in southern Mexico, Central America, and northern South America (references in USFWS 2002). River systems where the flycatcher persists in California include the Colorado, Owens, Kern, Mojave, Santa Ana, Pilgrim Creek, Santa Margarita, San Luis Rey, San Diego, San Mateo Creek, San Timoteo Creek, Santa Clara, Santa Ynez, Sweetwater, San Dieguito, and Temecula Creek (see references in USFWS 2002). Common tree and shrub species that comprise nesting habitat include willows (Salix spp.), seepwillow (aka mulefat; Baccharis spp.), boxelder (Acer negundo), stinging nettle (Urtica spp.), blackberry (Rubus spp.), cottonwood (Populus spp.), arrowweed (Tessaria sericea), tamarisk (aka saltcedar; Tamarix ramosissima), and Russian olive (Eleagnus angustifolia) (see references in USFWS 2002).

List Status


Habitat Affinities

Breeds in relatively dense riparian tree and shrub communities associated with rivers, swamps, and other wetlands, including lakes/reservoirs; most are classified as forested wetlands or scrub-shrub wetlands [1]. Breeds from near sea level to >2,600 m (8,500’) but primarily in lower-elevation areas [1]. Appendix G in USFWS (2002) has extensive description of habitat associations. E. t. extimus almost always nests near surface water or saturated soil (references in USFWS 2002). In some cases a site may dry out, but riparian vegetation and nesting flycatchers may persist 1-2 breeding seasons before they are eventually lost. Often cluster territories into small portions of riparian sites; major portions of site may be occupied irregularly or not at all (references in USFWS 2002).

Taxonomy and Genetics

Four subspecies separated in breeding ranges & distinguished primarily by subtle differences in color and morphology [2]. Paxton (2000 in USFWS 2002) concluded E. t. extimus is genetically distinct from other willow flycatcher subspecies. Recent research found substantial genetic variation within and among flycatcher breeding groups, and within and between watersheds (references in USFWS 2002).

Seasonal Activity

Range-wide, typically arrive on breeding grounds early May to early June; a few may establish territories in very late April (references. in USFWS 2002). Typical arrival first week of May in southern California and Arizona [2]. Males usually arrive first at breeding site and establish territory [1]. Females tend to arrive ~1-2 weeks later.

Life History/Reproduction

Typical clutch size 3-4 eggs; 12-13 d incubation [1,3]. Second nest attempts after successful fledging of first nest are rare; mostly occur if young fledge by late June or early July. Female may attempt up to 4 nests in a season if attempts lost to predation, parasitism, or disturbance (Smith et al. 2002 in USFWS 2002). Fecundity reduced by factors such as nest predation and brood parasitism by brown-headed cowbird (Molothrus ater). Recovery Plan [1] estimated ~900-1100 pairs range-wide. Another estimate based on 1993-1996 surveys was 549 territories with a minimum of 70% documented as confirmed or probable breeding pairs [4]. Breeding behavior must be confirmed to conclude an observation of willow flycatcher is E. t. extimus since migrating flycatchers in San Diego County may be E. t. brewsteri [2]. E. t. brewsteri breeding range extends from central California coast north, through western Oregon and Washington to Vancouver Island.

Diet and Foraging

Insectivorous. Captures prey on the wing or by gleaning in and above dense riparian vegetation (referemces. in USFWS 1993). Also forages in areas adjacent to nest sites which may be more open [6]. Diet studies [7] indicate a wide range of prey consumed. Major prey ranged from small (flying ants) to large (dragonflies) flying insects; Hymenoptera, Diptera and Hemiptera comprised half of prey items.


Fledglings typically stay in nest area minimum 14-15 d after fledging, possibly much longer [1]. One action identified in Recovery Plan is “survey to determine dispersal movements and colonization events.” Multi-year studies of color-banded birds showed although most returned to former breeding areas, flycatchers regularly moved among sites within and between years (references in USFWS 2002). In one 3-year study 66%-78% of flycatchers known to have survived from one breeding season to the next returned to the same breeding site; 22% -34% of returning birds moved to different sites (Luff et al. 2000 in USFWS 2002).


Threats/limiting factors include extensive loss and modification of breeding habitat and threat of increased brood parasitism by cowbirds [1]. Riparian decline caused mainly by: reduction or elimination of surface and subsurface water from diversion and groundwater pumping; changes in flood and fire regimes from dams and stream channelization; clearing and controlling vegetation; livestock grazing; changes in water and soil chemistry due to disruption of natural hydrologic cycles; and invasive non-native plants.

Special Considerations:

For a thorough review of the influence of cowbird parasitism, including recommendations on when management actions are warranted, consult Appendix F in Recovery Plan [2]. Of the states where this sub-species breeds, parasitism by brown-headed cowbirds has the greatest impact in California; the largest population in California consistently experienced rates of at least 50% in the absence of cowbird control [1]. The Recovery Plan notes that it is important to consider that the presence of cowbird parasitism does not necessarily mean it is having significant effects on a given flycatcher population. The Recovery Plan identifies multiple specific actions in the following nine areas to promote increased populations: (1) increase and improve currently suitable and potentially suitable habitat; (2) increase metapopulation stability; (3) improve demographic parameters; (4) minimize threats to wintering and migration habitat; (5) survey and monitor; (6) conduct research; (7) provide public education and outreach; (8) assure implementation of laws, policies, and agreements that benefit the flycatcher; (9) track recovery progress. Overuse by livestock has been a major factor in the degradation and modification of riparian habitats in the western U.S., with effects including changes in plant community structure, species composition, and relative abundance of species and plant density [6]. Invasion by tamarisk (Tamarix sp.) and giant reed (Arundo donax) have also altered native riparian communities.

Literature Sources

[1] U.S. Fish and Wildlife Service. 2002. Final Recovery Plan Southwestern Willow Flycatcher (Empidonax traillii extimus). Prepared by Southwestern Willow Flycatcher Recovery Team Technical Subgroup. Prepared for Region 2 U.S. Fish and Wildlife Service, Albuquerque, New Mexico 87103. August 2002. 210 pp., Appendices A-O.

[2] Unitt, P. 1987. Empidonax traillii extimus; An endangered subspecies. Western Birds 18:137-162.

[3] Sedgwick, J. A. 2000. Willow flycatcher Empidonax traillii. No. 533. In The Birds of North America. A. Poole and F. Gill, Eds. Cornell Laboratory of Ornithology, N.Y. and The Academy of Natural Sciences, Washington D. C.

[4] Marshall, R.M. 2000. Chapter 2: Population status on breeding grounds, pp.3-11 In Finch, D. M. and S. H. Stoleson, eds. 2000. Status, ecology, and conservation of the southwestern willow flycatcher. Gen. Tech. Rep. RMRS-GTR-60. Ogden, UT: U.S. Department of Agriculture, forest Service, Rocky Mountain Research Station. 131 pp.

[5] U.S. Fish and Wildlife Service. 1993. Endangered and Threatened Wildlife and Plants; Proposed Rule to List the Southwestern Willow Flycatcher as Endangered with Critical Habitat. Federal Register 58:39495-39522.

[6] U.S. Fish and Wildlife Service. 1995. Endangered and Threatened Wildlife and Plants; Final Rule Determining Endangered Status for the Southwestern Willow Flycatcher. Federal Register 60:10693-10715.

[7] Drost, C.A., E. H. Paxton, M. K. Sogge, and M. J. Whitfield. 2001. Food Habits of the Endangered Southwestern Willow Flycatcher. Final Report to the U.S. Bureau of Reclamation, Salt Lake City January 2001.