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Lower Colorado River Multi-Species Conservation Program Balancing Resource Use and Conservation

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Southwestern Willow Flycatcher

      (Empidonax traillii extimus)

Southwestern Willow Flycatcher nestSouthwestern Willow FlycatcherSouthwestern Willow Flycatcher chick

General Description

The southwestern willow flycatcher (Empidonax traillii extimus) is a small neotropical migrant that primarily lives along riparian corridors in dense trees and shrubs. These riparian habitats are associated with rivers, wetlands, lakes, and reservoirs.

The flycatcher is approximately 5.75 inches (15 cm) long, and weighs approximately 0.4 oz (12 g). It has a grayish-green back and wings, whitish throat, light grey-olive breast, and pale yellow belly. Two distinct wing bars are visible on the greater coverts, and an eye-ring is either absent or very faint. The upper mandible is dark, while the lower mandible is pale to yellowish.

Legal Status

The southwestern willow flycatcher was designated by the U.S. Fish and Wildlife Service as endangered on February 27, 1995. This subspecies was listed under the California Endangered Species Act as endangered in 1990, and is on the list of Arizona Wildlife of Special Concern. A final recovery plan was completed in 2002 and the designation of critical habitat was finalized in 2005. Critical habitat is in the process of being revised. 


The willow flycatcher is one of 10 species in the genus Empidonax (meaning gnat or mosquito king). The southwestern willow flycatcher (Empidonax traillii extimus) is now recognized as one of four, or possibly five, subspecies of the willow flycatcher. These species are separated by geographic and/or environmental boundaries.


The southwestern willow flycatcher breeds across the lower southwestern United States from May through August. Southwestern willow flycatcher typically arrive on the breeding grounds between early May and early June. Males generally arrive first to set up territories, with females arriving a week or two later. Males are highly territorial and will defend their territory through counter singing and aggressive interaction. Males are usually monogamous, but polygyny does occur. Multi-year color banding studies have shown high site fidelity among after-second-year birds returning to former breeding patches.

Territory size varies greatly, potentially due to population density, habitat quality, and nesting stage. Flycatchers’ home ranges are greater than their territories and can vary in size depending on breeding status and surrounding habitat areas. Territoriality is also maintained on the wintering grounds.

Southwestern willow flycatchers build open cup nests that are typically placed within the fork of branches with the nest cup supported by several stems. Nest height varies and can be anywhere from ground height to several meters high, depending on height of nest tree. Flycatchers nest in various tree species including Goodding’s willow, coyote willow, cottonwood, salt cedar, and other native and exotic tree species. Nest building usually begins 3-7 days after pair formulation. On average, one egg is laid per day, with a typical clutch size of four eggs laid within 5 days. Egg laying can start as early as late May, but is usually in early to mid-June. Willow flycatcher eggs are tan to buffy in color, with a few brown spots on one end. Upon completion of egg laying, the female usually incubates the eggs for approximately 12 days. Nestlings fledge usually within 12-15 days. Southwestern willow flycatchers can re-nest, either after the first nest fledges or after failure, and have been documented to have up to four nesting attempts and three clutches.


The southwestern willow flycatcher is an insectivore that hawks insects while in flight, gleans insects from foliage, and occasionally captures them from the ground. The main diet of the flycatcher consists of small to medium size insects such as true bugs, wasps and bees, flies, beetles, butterflies and caterpillars, and spiders. Berries and small fruits have also been reported but are typically rare. The flycatcher can exploit a diverse array of insects depending on availability within the habitat between sites and between years depending on abundance and availability of insects in and near the breeding habitat.


Habitat alteration, as well as loss and fragmentation are considered one of the greatest threats to the southwestern willow flycatcher. Riparian habitats in the Southwest are naturally patchy and subject to periodic disturbance. Factors contributing to habitat loss include fire, water management, such as dams and reservoirs, diversions and groundwater pumping, channelization and bank stabilization, agricultural development, livestock grazing, increased recreation, and urbanization. All of these cause loss of habitat, habitat fragmentation, loss of critical water underneath stands, and human disturbance.

Riparian habitat along the LCR alone has drastically changed from a cottonwood-willow dominated habitat, including approximately 89,200 acres of potential willow flycatcher breeding habitat, to over 80,000 acres of salt cedar, with no over-bank flooding to help rejuvenate native riparian stands.

The southwestern willow flycatcher has evolved with predation and cowbird parasitism, but increased populations of predators and cowbirds have become a major threat to some local populations. Predation is the leading cause of nest failure in many populations of southwestern willow flycatcher, including those along the LCR and its tributaries. Known and suspected nest predators include snakes, predatory birds such as raptors, corvids, grackles and cowbirds, small mammals, and even ants.

More Information

Additional information on this species, as well as source documentation, can be found in the species accounts located at this link (PDF). A fact sheet on this species can be found here. The Conceptual Ecological Model (CEM) can be found here (PDF). Technical Reports on this species can be found here.

Updated January 7, 2020

The historic breeding range of the southwestern willow flycatcher included southern California, southern Nevada, southern Utah, Arizona, New Mexico, western Texas, southwestern Colorado, and extreme northwestern Mexico. According to the critical habitat designation for southwestern willow flycatcher, the current occupied geographic area crosses six southwestern states including southern California, southern Nevada, southern Utah, southern Colorado, Arizona, and New Mexico, from sea level to approximately 8000 feet (2438 m) above sea level. In general, flycatcher distribution occurs mainly in lower elevation riparian habitat, with a few patches distributed in relatively small isolated locations. According to the Southwestern Willow Flycatcher Recovery Plan, approximately 53% of the known population is found in 10 breeding sites range-wide, while the other 47% are distributed among approximately 100 small sites of 10 or fewer territories.

Wintering grounds for the willow flycatcher include portions of southern Mexico, Central America, and northern South America. Specific surveys have been conducted at sites in El Salvador, Costa Rica, Panama, Mexico, Ecuador, Nicaragua, and Guatemala. It is suspected that all subspecies may winter in similar locations. Because it is difficult to identify subspecies of willow flycatchers.

The southwestern willow flycatcher breeds in dense riparian vegetation near surface water or saturated soil, across a large elevation and geographic area. Dominant plant species consist of large riparian trees such as coyote willow, Goodding’s willow, Fremont cottonwood, box elder, and nonnative saltcedar and Russian olive. Occupied sites vary in size and shape but all are relatively dense, with some open areas, and are usually associated with open or standing water. Although most of the sites are associated with open water, marshy seeps, or saturated soil where the nest tree can be in standing water, hydrologic conditions can change drastically during the breeding season and between years. Because birds are exposed to extreme environmental conditions throughout the desert southwest, the presence of water is an important component of flycatcher habitat.

Habitat characteristics on the wintering grounds for the willow flycatcher are similar to the characteristics of the breeding habitat. Wintering habitats are strongly associated with standing water and/or saturated soils, patches or stringers of riparian species of trees, woody understory, and open areas such as pastures, savannas, or bodies of water with forested edges.

LCR MSCP Conservation Measures

The Habitat Conservation Plan provides conservation measures specific to each species. Listed below are the species specific conservation measures for the southwestern willow flycatcher. Click on the arrows to expand the table.

WIFL1—Create 4,050 acres of southwestern willow flycatcher habitat

Of the 5,940 acres of created cottonwood-willow, at least 4,050 acres will be designed and created to provide habitat for this species. Created cottonwood-willow will be designed and managed to support cottonwood-willow types I–IV that provide breeding habitat for this species. The created cottonwood-willow would also function as migration habitat for birds that migrate along the LCR. A total of 2,700 acres of created habitat will be designed and managed to provide habitat for both the southwestern willow flycatcher and yellow-billed cuckoo. To provide habitat for both species, created habitat will need to be composed of cottonwood-willow types I–IV, include moist soils for flying insect production, and be in large habitat blocks (at least 25 acres but preferably up to 200 or more acres). The remaining 1,350 acres of the 4,050 acres of created habitat will also be composed of cottonwood-willow types I–IV and will include moist soils, but patches of this habitat may be smaller if site constraints limit the construction of larger habitat patches.

Of the 1,350 acres of habitat to be created specifically for the yellow-billed cuckoo (Section 5.7.14 in the HCP), patches that provide surface water or moist surface soil conditions during the breeding season will also support habitat for the southwestern willow flycatcher. In addition to the spatial replacement of affected habitat, the quality of created habitat will be substantially greater than the affected habitat. Affected southwestern willow flycatcher habitat is dominated by dense stands of saltcedar that support little vegetative diversity relative to the cottonwood-willow land cover that will be created and managed as flycatcher breeding habitat. Cottonwood-willow land cover created to provide southwestern willow flycatcher habitat will be designed and managed to be dominated by native riparian trees (i.e., cottonwood and willow trees), support flying insect production used as food by the flycatcher, support a diversity of plant species, provide a dense multilayered canopy, support multiple seral stages, and provide substantial areas of edge habitat. Created habitat, thus, will be similar to the condition of the species' native habitat that was historically present along the LCR. The relative suitability and carrying capacity of saltcedar and cottonwood-willow habitats for nesting southwestern willow flycatchers are difficult to measure under current conditions because saltcedar now dominates most riparian areas along the LCR. Based on historical accounts, however, cottonwood-willow forests of the LCR once supported a high diversity and density of nesting birds, including willow flycatchers (Grinnell 1914; Garrett and Dunn 1981; Rosenberg et al. 1991). Thus, it is reasonable to assume that the successful replacement of the current saltcedar-dominated habitats by the species' historical, native habitat would provide highly favorable conditions for long-term maintenance and enhancement of southwestern willow flycatcher populations on the LCR.

To ensure that high quality and fully functioning southwestern willow flycatcher breeding habitat is created, the following design and management criteria, subject to adjustment through the LCR MSCP adaptive management process, will be applied to created cottonwood-willow land cover dedicated as replacement southwestern willow flycatcher habitat:

  • Southwestern willow flycatcher habitat will be created in patches of at least 10 acres, with an objective of creating larger patches of habitat.
  • Created-habitat patches will be close to each other or existing tracts of riparian forest that provide southwestern willow flycatcher habitat in a manner that will maximize continuity with other riparian habitats.
  • Designs of created habitats will emphasize creation of nesting habitat within 200 feet of standing or slow-moving water or moist surface soils (suitable insect-productive foraging habitats) and will include creation of suitable habitat edges that are preferred by this species.
  • Created habitat will include provisions for supporting moist surface soils and standing or slow-moving water required by the species within their territories during the breeding season (may extend from late April to August along the LCR). Maintaining these conditions could involve creation of canals and shallow swales that permanently or seasonally maintain surface water or moist surface soil conditions. Because the actual period that moist soils or ponded or slow-moving water conditions must be present to support successful reproduction is not well understood, watering of created habitat will be managed adaptively to determine periods when water must be present to support flycatcher reproduction.
  • Canals and shallow swales may need to be created to dissect blocks of created cottonwood-willow that will be wide enough (estimated to be at least 25 feet) to create interior forest-edge conditions necessary to support southwestern willow flycatcher habitat, create the microrelief and soil moisture conditions necessary to support a diversity of understory plant species, and supply irrigation water.
  • Created habitat will be designed and actively managed to support a vigorous plant community that will support multiple layers, seral stages, and age cohorts of trees.
  • Mounds and depressions, to the extent necessary, will be created in habitat created on conservation areas to establish some topographic diversity that will also provide habitat diversity by increasing plant and insect prey species diversity.
WIFL2—Maintain existing important habitat areas
The Applicants, under agreements with cooperating land management agencies, will provide funding to those agencies to maintain a portion of existing southwestern willow flycatcher habitat within the LCR MSCP planning area (Section 5.4.2 in the HCP). Maintaining important existing habitat areas is necessary to ensure the continued existence of the southwestern willow flycatcher in the LCR MSCP planning area, provide for the production of individuals that could disperse to and nest in LCR MSCP–created habitats, and support future recovery of the species.
MRM1—Conduct surveys and research to better identify covered and evaluation species habitat requirements
Conduct surveys and research, as appropriate, to collect information necessary to better define the species habitat requirements and to design and manage fully functioning created covered and evaluation species habitats. This conservation measure applies to those species for which comparable measures are not subsumed under species-specific conservation measures (Section 5.7 in the HCP)). They are not applicable to species for which habitat would not be created under the LCR MSCP Conservation Plan, such as the desert tortoise, relict leopard frog, humpback chub, and threecorner milkvetch.
MRM2—Monitor and adaptively manage created covered and evaluation species habitats
Created species habitats will be managed to maintain their functions as species habitat over the term of the LCR MSCP. Created habitat will be monitored and adaptively managed over time to determine the types and frequency of management activities that may be required to maintain created cottonwood-willow, honey mesquite, marsh, and backwater land cover as habitat for covered species. This conservation measure applies to those species for which comparable measures are not subsumed under species-specific conservation measures (Section 5.7 in the HCP). They are not applicable to species for which habitat would not be created under the LCR MSCP Conservation Plan, such as the desert tortoise, relict leopard frog, humpback chub, and threecorner milkvetch.
MRM4—Conduct research to determine and address the effects of brown-headed cowbird nest parasitism on reproduction of covered species
Research will be undertaken to determine whether brown-headed cowbird nest parasitism is a substantial factor limiting the reproductive success of the southwestern willow flycatcher, vermilion flycatcher, Arizona Bell's vireo, Sonoran yellow warbler, and summer tanager in the LCR MSCP planning area. If so, studies will be implemented to identify effective and practical methods for controlling brown-headed cowbirds. If cowbirds are adversely affecting breeding success and effective control measures are developed, a program will be implemented to monitor the effects of cowbirds on nesting success in LCR MSCP–created habitats to determine the need for cowbird control and to implement cowbird control measures in locations where cowbird control is needed to improve reproductive success.
CMM1—Reduce risk of loss of created habitat to wildfire
Management of LCR MSCP conservation areas will include contributing to and integrating with local, state, and Federal agency fire management plans. Conservation areas will be designed to contain wildfire and facilitate rapid response to suppress fires (e.g., fire management plans will be an element of each conservation area management plan).
CMM2—Replace created habitat affected by wildfire
In the event of created-habitat degradation or loss as a result of wildfire, land management and habitat creation measures to support the reestablishment of native vegetation will be identified and implemented.
AMM1—To the extent practicable, avoid and minimize impacts of implementing the LCR MSCP on existing covered species habitats
To the extent practicable, establishment and management of LCR MSCP–created habitats will avoid removal of existing cottonwood-willow stands, honey mesquite bosques, marsh, and backwaters to avoid and minimize impacts on habitat they provide for covered species. Temporary disturbance of covered species habitats, however, may be associated with habitat creation and subsequent maintenance activities (e.g., controlled burning in marshes and removal of trees to maintain succession objectives). LCR MSCP conservation measures that could result in such temporary disturbances will, to the extent practicable, be designed and implemented to avoid or minimize the potential for disturbance. In addition to implementing AMM3 and AMM4 below, these measures could include conducting preconstruction surveys to determine if covered species are present and, if present, implementing habitat establishment and management activities during periods when the species would be least sensitive to those activities; or redesigning the activities to avoid the need to disturb sensitive habitat use areas; staging construction activities away from sensitive habitat use areas; and implementing BMPs to control erosion when implementing ground disturbing activities.
AMM2—Avoid impacts of flow-related covered activities on covered species habitats at Topock Marsh

Impacts on groundwater levels that support covered species habitat at Topock Marsh will be avoided by maintaining water deliveries for maintenance of water levels and existing conditions. At times, flow-related activities could lower river elevations to levels that could disrupt diversion of water from the river to the marsh.  Improvements to intake structures that allow water to continue to be diverted or other measures to maintain the water surface elevation will avoid effects on groundwater elevation. Avoidance of effects could be accomplished with the purchase, installation, and operation of two electric pumps sized to the current inflow at the Topock Marsh diversion inlet. The pumps would most likely need to be operated during summer to make up for the lower flow periods.

Implementation of this conservation measure would maintain existing habitat at Topock Marsh for the Yuma clapper rail, southwestern willow flycatcher, Colorado River cotton rat, western least bittern, California black rail, yellow-billed cuckoo, gilded flicker, vermilion flycatcher, Arizona Bell's vireo, and Sonoran yellow warbler. The extent of covered species habitat impacts that will be avoided by maintaining water deliveries to Topock Marsh are presented in Table 4-2 in the HCP. Maintaining water deliveries to Topock Marsh will also maintain razorback sucker and bonytail habitat associated with disconnected backwaters managed for these species.
AMM3—To the extent practicable, avoid and minimize disturbance of covered bird species during the breeding season

To the extent practicable, to avoid and minimize potential impacts on covered bird species, vegetation management activities (e.g., periodic removal of emergent vegetation to maintain canals and drains) associated with implementation of covered activities and the LCR MSCP that could result in disturbance to covered bird species will not be implemented during the breeding season to prevent injury or mortality of eggs and young birds unable to avoid these activities. Table 5-9 in the HCP describes the breeding period for each of the covered species during which, to the extent practicable, vegetation management activities in each species' habitat will be avoided.

AMM5—Avoid impacts of operation, maintenance, and replacement of hydroelectric generation and transmission facilities on covered species in the LCR MSCP planning area

To the extent practicable, before implementing activities associated with OM&R of hydroelectric generation and transmission facilities, measures will be identified and implemented that are necessary to avoid take of covered species where such activities could otherwise result in take. These measures could include conducting surveys to determine if covered species are present and, if so, deferring the implementation of activities to avoid disturbance during the breeding season; redesigning the activities to avoid the need to disturb covered species habitat use areas; staging of equipment outside of covered species habitats; delineating the limits of vegetation control activities to ensure that only the vegetation that needs to be removed to maintain infrastructure is removed; stockpiling and disposing of removed vegetation in a manner that minimizes the risk of fire; and implementing BMPs to control erosion when implementing ground disturbing activities.

AMM6—Avoid or minimize impacts on covered species habitats during dredging, bank stabilization activities and other river management activities

To the extent practicable, before initiating activities involved with river maintenance projects, measures will be identified and implemented that avoid or minimize take of covered species where such activities could otherwise result in take. Such measures could include alternative methods to achieve project goals, timing of activities, pre-activity surveys, and minimizing the area of effect, including offsite direct and indirect effects (e.g., avoiding or minimizing the need to place dredge spoil and discharge lines in covered species habitats; placing dredge spoils in a manner that will not affect covered species habitats).

Research and Monitoring Activities

LCR MSCP conduct a variety of research and monitoring activities along the LCR encompassing both MSCP and non-MSCP species. For a complete list of all activities, please see the Research and Monitoring Activities web page.

This gallery includes photos of this species. If you require larger photos, please contact our webmaster Michelle Reilly at mreilly@usbr.gov.

Banded southwestern willow flycatcher at Mesquite West, near Mesquite, NV - Photo by Reclamation Southwestern willow flycatcher nest - Photo by Reclamation Southwestern willow flycatcher nestling on the lower Colorado River - Photo by Reclamation Southwestern willow flycatcher nestlings at Planet Ranch, on the Bill Williams River, near Parker, AZ - Photo by Reclamation Migrating willow flycatcher at Beal Restoration Site, in Havasu National Wildlife Refuge, near Needles, CA - Photo by Reclamation