Some recent research suggests there may be a fifth subspecies (E.t. campestris) distinct from E.t. traillii and occupying breeding areas in the northern and western portions of E.t. traillii range.
The breeding range distribution of the races of the Willow Flycatcher. Modified from Unitt (1987) and Browning (1993).
The Southwestern Willow Flycatcher breeds in dense riparian habitats along rivers, streams, or other wetlands. The vegetation can be dominated by dense growths of willows (Salix sp.), seepwillow (Baccharis sp.), or other shrubs and medium-sized trees. There may be an overstory of cottonwood (Populus sp.), tamarisk (Tamarix sp.), or other large trees, but this is not always the case. In some areas, the flycatcher will nest in habitats dominated by tamarisk and Russian olive (Eleagnus angustifolia). One of the most important characteristics of the habitat appears to be the presence of dense vegetation, usually throughout all vegetation layers present.
Almost all Southwestern Willow Flycatcher breeding habitats are within close proximity (less than 20 yards) of water or very saturated soil. This water may be in the form of large rivers, smaller streams, springs, or marshes. At some sites, surface water is present early in the nesting season, but gradually dries up as the season progresses. Ultimately, the breeding site must have a water table high enough to support riparian vegetation.
Photographs of a few known Southwestern Willow Flycatcher breeding areas are shown below. These examples are presented to show the wide diversity of sites where flycatchers have been found to breed.
Alpine, AZ, near the San Franciso River. Elevation approximately 8000 feet. Habitat is composed of a matrix of dense Geyer's Willow, approximately 3-4 m high. Soil is saturated most of the breeding season, but no open water nearby.
Roosevelt Lake, AZ, near the Salt River inflow. Elevation approximately 4000 feet. Habitat is composed of an extremely dense tamarisk monoculture, approximately 25-30 feet high. The vegetation is rooted in standing water some years, but in other years the soil has dried by the late breeding season.
Verde River, AZ, along the Verde River. Elevation approximately 4500 feet. Habitat is composed of a dense multi-storied mixture of tamarisk and native vegetation, ranging from 20-40 feet high. The overstory is dominated by tall cottonwoods. The patch is adjacent to the Verde River, and has a small spring-fed stream running throughout.
San Marcial, NM, along the Rio Grande. Elevation approximately 3000 feet. Habitat is composed of a dense multi-storied mixture of tamarisk and native vegetation, ranging from 20-30 feet high. The patch is adjacent to the Rio Grande, and may be flooded during high water years but dry later in the season.
The Southwestern Willow Flycatcher has declined during the last 100 years, primarily due to the loss, fragmentation, and modification of riparian habitats. In 1993, the U.S. Fish and Wildlife Service formally proposed to list the flycatcher as a federal endangered species, and to designate critical habitat (Federal Register 58:pages 39495-39522, July 23, 1993). In a 1995 ruling, the Service found that the flycatcher population was currently very low and faced a significant threat of extinction unless protected. Therefore, the flycatcher was listed as endangered, but designation of critical habitat was postponed (Federal Register 60:10694-10715, February 27, 1995).
Based on recent surveys coordinated by various state and federal agencies, fewer than 500 breeding pairs of the Southwestern Willow Flycatcher remain throughout its range. Surveys have also shown that the breeding sites are widely scattered and isolated, and most sites include fewer than five breeding pairs.
There are four or five recognized subspecies (races) of the Willow Flycatcher (Empidonax traillii). These subspecies are distinguished primarily by subtle differences in color and morphology (size and shape). The Southwestern Willow Flycatcher is somewhat paler, and has slightly different wing and tail length ratios. Each of the four subspecies occupy distinct breeding ranges.
The flycatcher population has clearly declined, and is currently very small and fragmented. However, with effective protection of the flycatcher and its remaining breeding habitat, combined with restoration and enhancement of southwestern riparian systems, the Southwestern Willow Flycatcher may recover and continue as a valuable component of our riparian ecosystems.
Lend your support to the protection and enhancement of riparian habitats, particularly in the arid southwest. If you know of a site where Southwestern Willow Flycatchers are breeding, contact your state or federal wildlife agency contacts.Let your local, State, and Federal officials know your position regarding conservation of the Willow Flycatcher and other neotropical migrants and their riparian habitats.
Keep informed through local and regional conservation groups about activities that may affect neotropical migratory birds and their habitats.
Increase our understanding of the status and distribution of all neotropical migratory birds in Arizona by participating in the Arizona Breeding Bird Atlas Project.
One of the goals of the APIF Master Plan is to "identify and set priorities for research needs and facilitate research for neotropical migratory birds and their habitats in Arizona" (Sferra et al. 1994). In partial fulfillment of this goal the following list has been developed for the southwestern willow flycatcher. This list was compiled from conversations with agency resource managers and biologists, agency and private researchers currently working on the flycatcher, and from recommendations in reports or published literature on the flycatcher. This draft list is constantly evolving as new data or management actions raise new questions. Priority or rankings have not been assigned. Future additions are likely, all comments are welcome.
2. Need: Southwestern willow flycatcher breeding sites are widely scattered across the regional landscape. Given the large amount of area surveyed, as well as the
large number of people and agencies conducting surveys, it is critical that a system be developed to record and track known flycatcher breeding sites, unoccupied
areas that have been surveyed, and areas that should be surveyed. Such a system will enable managers and researchers to (1) understand the ecosystem and
landscape aspects of flycatcher distribution and habitat use, (2) effectively monitor what sites have been surveyed (to avoid duplication of effort), (3) determine
where future efforts should be directed, and (4) develop a management tool for evaluating and implementing habitat conservation.
Task: Database/GIS of survey
data and potential habitat (e.g., all sites surveyed; historic locations, extant locations, breeding status).
Scale: Rangewide (consolidate data from all states).
Target Initiation Date: 1996.
Duration of Study: One year initial focused effort with annual or biennial updates as population distribution changes.
4. Need: Research, inventory, and conservation efforts undertaken for the southwestern willow flycatcher must be based on a quantitative understanding of
flycatcher habitat. Currently, flycatcher habitat is measured and quantified differently by various researchers and agencies, making detection of general patterns and
comparisons among sites difficult.
Task: Develop and implement quantitative habitat descriptions of riparian patches, territories, and nest sites occupied by
flycatchers (e.g., vegetation characteristics, topographical setting, hydrological characteristics, environmental characteristics of nest sites).
Scale: Local,
site-specific, regional, and rangewide incorporating mixed riparian, monotypic native, and monotypic exotic habitats.
Target Initiation Date: 1996.
Duration of Study: In conjunction with ongoing survey/monitoring for a minimum of five years.
6. Need: Patterns of population demography (birth, death, productivity, survivorship, etc.) are the factors that govern flycatcher population size and trend.
Knowledge of demography patterns in combination with dispersal and emigration/immigration data are critical for identifying populations that should receive priority
for management.
Task: Population demography of adult and immature flycatchers including productivity of females and survivorship of adults and immatures.
Scale: Local monitoring at sites throughout range.
Target Initiation Date: 1996.
Duration of Study: Minimum 3 to 5 years.
7. Need: As a suboscine, willow flycatcher vocal behaviors are more likely influenced by genetics rather than learning, as is the case for oscine songbirds. The
southwestern willow flycatcher appears to have a primary song that is distinguishable from other flycatcher subspecies. If confirmed, song could be used to
distinguish birds in the field eliminating the need to capture birds for positive identification. In addition, subspecific song patterns may yield important data relative to
the distribution of and degree of differentiation between flycatcher subspecies.
Task: Expand current flycatcher vocalization study to determine local/population
and/or sub-specific differences in primary song throughout range.
Scale: Throughout range of Empidonax traillii extimus, E.t. brewsteri, E.t. adastus, E.t.
campestris.
Target Initiation Date: 1996.
Duration of Study: 2 years.
8. Need: Southwestern willow flycatcher breeding populations are extremely small and widely-separated. Some breeding populations may be isolated. Species
with these characteristics often have low genetic diversity, with potential for low productivity and survivorship. Management and recovery of the flycatcher should
be guided, in part, by an understanding of current population genetics at local and regional scales in order to preserve maximum genetic diversity.
Task: Determine
current genetic variability for E.t. extimus rangewide.
Scale: Rangewide sampling including small and large populations, isolated (e.g. Big Sandy, Grand Canyon)
and non-isolated populations (e.g., San Pedro River, Kern river, Rio Grande in NM).
Target Initiation Date: 1996.
Duration of Study: 2 years.
9. Need: The southwestern willow flycatcher was formerly more common and widespread, and breeding populations were less isolated. Consequently, it is
assumed that genetic diversity was higher at both local and regional scales. A large number of museum specimens were collected at the turn of the century across
the species' range, and provide material for determining historic levels and patterns of genetic diversity. These can be compared with current patterns (see # 8
above) and used to evaluate genetic and conservation consequences of population fragmentation and decline.
Task: Determine historic genetic variability from
museum specimens used in Unitt's (1987) status and distribution paper.
Scale: Range-wide contingent upon availability of museum specimens.
Target Initiation Date: 1997.
Duration of Study: 2 years.
10. Need: There are currently four or five recognized subspecies of the willow flycatcher in North America. Taxonomic evaluations have been based on subtle
differences in plumage coloration and body measurements. These characteristics are more difficult to distinguish in areas where putative subspecies intergrade, such
as in central Utah and southwestern Colorado where E.t. adastus may occur. Although genetic studies have been undertaken to support separation of the willow
and alder flycatchers, genetic studies on the validity of currently accepted flycatcher subspecies have not been conducted.
Task: Determine genetic basis for
subspecies of willow flycatcher.
Scale: Rangewide for all putative subspecies.
Target Initiation Date: 1996.
Duration of Study: 2 years.
12. Need: Conservation and management of this neotropical migratory species should include an understanding of its non-breeding season habitat use and ecology,
as reflected in current patterns of distribution. In addition, we need to determine critical winter and migration habitats so that an assessment of their conservation
needs can be made.
Task: By conducting intensive, standardized flycatcher surveys on potential wintering grounds, determine current distribution of southwestern
willow flycatchers during non-breeding season.
Scale: Begin by surveying historic locations rangewide as determined by above museum work and expand to
include other potential wintering areas as funding and effort allow.
Target Initiation Date: 1997.
Duration of Study: 3 - 4 years.
15. Need: A significant number of flycatcher breeding sites are near roads, bridges, recreation areas, or areas of anticipated road maintenance or construction.
Several studies suggest that roads and other disturbances may have a negative affect on locally breeding birds, both through direct collision impact and by reducing
local breeding productivity. Given the small size and number of flycatcher breeding populations, it is important to understand how a breeding area may be affected
by human activities noted above.
Task: Determine effects of ambient noise levels resulting from potential sources of disturbances (e.g. traffic, construction) on
breeding behavior of flycatchers.
Scale: Project specific locations plus control sites.
Target Initiation Date: 1996.
Duration of Study: Agency action-driven, at
least one year per site.
16. Need: Willow flycatcher populations experiencing brood parasitism by the brown-headed cowbird have declined or, at a minimum, have had reduced
productivity. Cowbird control programs have stabilized flycatcher populations in some areas, and may be an effective tool for minimizing cowbird impacts.
Cowbird control can be effective if implemented at cowbird concentration sites, if these sites can be determined. An understanding of daily and seasonal cowbird
movement patterns is important in effectively evaluating and managing the cowbird threat. We currently know little of cowbird population size and movement
patterns at the vast majority of flycatcher breeding sites.
Task: Utilize banding and radio-telemetry studies to determine local cowbird population characteristics
and movement patters.
Scale: Local, emphasizing areas with known cowbird parasitism.
Target Initiation Date: 1996.
Duration of Study: At least one year
per site.
Although widely distributed in the southwest, this bird is restricted to isolated tracts of breeding habitat and may be susceptible to habitat loss and climate change due to the owl¹s dependence on certain microhabitats that mimic mature forests. Dramatic climate change could profoundly alter the distribution and breeding density of spotted owls in the southwest United States through alterations in the extent of suitable habitat. In response to perceived threats by timber harvest, habitat loss due to fire, increased predation due to habitat fragmentation, and lack of adequate protective regulations, the Mexican spotted owl was listed as a threatened species in 1993.
Many aspects of the ecology of Mexican spotted owls have been documented in the southwest, particularly Arizona and New Mexico. In this region the owl is found associated with mixed conifer forest and uses mature stands more frequently than managed stands. In Utah, the owl primarily is associated with steep sandstone canyons with small patches of woodland habitat. Two studies in Utah described prey species found in regurgitated pellets and identified bushy-tailed woodrats (Neotoma cinerea), desert woodrats (Neotoma lepida) as the primary prey. The strong dependence on wood rats and the association with rocky canyonlands, suggests that spotted owls nest and forage primarily within non-forested areas in the state.
The Mexican Spotted Owl relies on cool and shady habitats in the southwest. The birds forage primarily on small rodents. Any climatic disturbance that would alter the distribution and phenology of plants within the forests, could alter the landscape in a negative way for both spotted owls and their small mammal prey. Changes in plant distribution and density could eliminate important nest and roost sites and cause extirpation of the small mammal prey. In addition, it is thought that spotted owls are heat intolerant and occupy dense forest in order to avoid high temperatures. Increases in ambient temperatures during the nest season could lead to nest failure and territorial abandonment. Ecologically, the owl appears to exhibit patterns of distribution strongly tied to dense and cool conifer forests. The majority of spotted owl nest sites that have been found in the southwest are located in mature forests. Owls that occupy the driest (or xeric) portions of their range will be threatened first, which could result in higher population fragmentation and genetic isolation. Given the threatened status of the owl, monitoring effects of climate change are highly warranted. It is critical that we continue to monitor habitat associations and vegetation, as well as spotted owl distributional patterns in the southwestern U. S., as climatologists document global warming patterns.
Aerial censuses found that wintering Bald Eagles were present each year along the Colorado River corridor from late fall (October -November) through early spring (March-April) (van Riper et al. 1995). Bald Eagles were generally distributed evenly along the river corridor except in January-February when conditions were suitable and rainbow trout were spawning (Leibfried and Montgomery 1993). During these 2 months birds concentrated at the small tributaries, such as Nankaweap Creek. The trend of Bald Eagle numbers at Nankaweap Creek closely followed numbers of spawning trout that were recorded in the creek. During 1990-91 van Riper and Sogge (1996) recorded the highest known Bald Eagle concentration in the southwest at Nankaweap Creek, with up to 26 eagles present on a peak day. Approximately 70 to 100 individual eagles were documented during the eagle concentration (that time when at least 10 eagles were present each day) from 8 February to 8 March 1990. The previous high of 18 wintering eagles was present at Nankoweap in February 1988 (Brown et al. 1989).
Bald Eagle numbers are greatly influenced by spawning fish, which are in turn greatly influenced by stream water levels. In those years of lower precipitation spawning does not occur (Leibfried and Montgomery 1993). With the onset of global warming, the precipitation pattern is predicted toward reduced levels in the southwest, which would mean fewer numbers of trout and birds. For example, in 1993 when spawning was extremely low in Nankaweap Creek, there were concomitantly low numbers of eagles. This bird does, however, have the ability to make long seasonal movements in search of food. During 1992-1994, with low wintering Bald Eagle numbers along the Colorado River, there were reported concentrations of Bald Eagles at other locations on the southern Colorado Plateau. During 1993 Arizona Game and Fish (pers comm) reported up to 20 eagles at Lake Mary, just east of Flagstaff, Arizona. These birds were feeding on the thousands of rainbow trout that the agency had stocked into the lake during the winter. In 1994, another year of low Bald Eagle numbers along the Colorado River corridor, there were numerous reports from state and federal agency biologists of small eagle concentrations at elk and deer carcasses over the southern Colorado Plateau.
The status of Bald Eagles (Haliaeetus leucocephalus) in the southwestern U.S., especially along portions of the Colorado River, could be greatly influenced by climatic changes. This is especially true as impacts of reduced precipitation negatively influence numbers fish in streams and lakes. For example, at Nankaweap Creek the trend went upward from a few birds starting in the mid 1980s, to peak numbers in 1990-1991. In following years (1992-1994), lower precipation patterns resulted in poor rainbow trout spawning and lower numbers of bald eagles frequenting this location. Creek morphology and flow conditions varied among years and influenced the availability of trout, and thus eagle numbers. However, the Bald Eagle concentration at Nankoweap can be the largest such concentration in the southwestern United States. The 70 to 100 individual eagles recorded during the 1990 concentration represent what is believed to be one-fourth of the entire population of Bald Eagles wintering to the south of the Grand Canyon (in Arizona and northern Mexico). Concentrations of Bald Eagles noted in other areas of the southern Colorado Plateau, when lower numbers were recorded along the Colorado River, suggest widespread eagle movements over the region. Bald Eagles appear to be concentrating in areas that have the most abundant and available food resources, and these locations would be reduced as precipitation declined from global warming.
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