Southwestern Willow Flycatcher Research Needs
Research and Data Needs for the Endangered
Southwestern Willow Flycatcher (Empidonax traillii extimus)
Rob Marshall
Research Committee Chair
Arizona Partners In Flight
U.S. Fish and Wildlife Service
Phoenix, Arizona
602-640-2720
November 1995
The Arizona Partners in Flight (APIF) Master Plan (Sferra et al. 1994) outlines a set of goals and objectives for inventory and monitoring, research, information and education, management, and international issues involving neotropical migratory bird species. A major focus of APIF has been a three-year survey and monitoring effort for the southwestern willow flycatcher, listed as endangered by the U.S. Fish and Wildlife Service on March 29, 1995. This effort has greatly enhanced our knowledge of the status and distribution of the flycatcher in Arizona. An additional result of this effort has been the formulation and refinement of research and data needs that bear directly on the management and overall recovery of this species.
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.
SURVEY/MONITORING
1. Need: Recent surveys have been conducted in many riparian areas region-wide and have increased our knowledge of the southwestern willow flycatcher's distribution and status. However, many areas of suitable or potential habitat remain unsurveyed. Given the low population and patchy distribution of this species, it is important to intensify efforts to find and verify all breeding sites. Task: Expand ground survey efforts to determine status/distribution in: CA - Santa Margarita River and tributaries, Santa Ynez River, Otai River, Sweetwater River; AZ - lower Colorado River, Bill Williams River, Gila River, Little Colorado River and tributaries; NM - Rio Grande; TX - Rio Grande, Pecos; CO -Dolores River; UT - Virgin River, Green River, San Juan River, Santa Clara River, Escalante River. Scale: Local, site-specific to regional. Target Initiation Date: 1996. Duration of Study: 3 - 4 years.
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.
HABITAT USE
3. Need: We are only beginning to understand how habitat patch size, shape, and proximity to water and other resources affects the suitability of habitat and the way in which flycatchers will use a site. Habitat patch characteristics of this scale can only be determined using high resolution aerial photographs. Aerial photographs are invaluable for mapping the distribution of territories at a breeding site and for aiding in estimating population size. Task: Obtain low-level aerial photos of habitat for extant breeding locations. Scale: All breeding locations rangewide. Target Initiation Date: 1996. Duration of Study: In conjunction with ongoing survey/monitoring efforts.
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.
POPULATION AND DEMOGRAPHIC STUDIES
5. Need: Of the approximately 40 currently known breeding sites rangewide, we have detailed data on breeding biology and population dynamics from only one site (Kern River in CA). Critical to the development of a conservation strategy or recovery plan is an understanding of flycatcher movement among breeding sites. Data on immigration/emigration rates and dispersal patterns are critical for understanding this species' dynamics across the entire range. Task: Determine patterns of philopatry/site fidelity, natal dispersal, and adult dispersal through banding studies and extensive regional presence/absence surveys. Scale: All local studies integrated at a regional level. Duration of Study: Minimum 3 to 5 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.
NON-BREEDING SEASON
11. Need: The southwestern willow flycatcher is a neotropical migrant wintering in Mexico, Central America, and northern South America. Therefore, it spends less than half of the year on its breeding grounds in the American Southwest. Conservation and management of the flycatcher requires knowledge of historic patterns of distribution to provide baseline information for an evaluation of current status, habitat use, and threats on its migration and wintering grounds (see # 12 below). Task: By locating historic specimens and records of willow flycatchers in the non-breeding season, determine historic distribution of southwestern willow flycatchers during the non-breeding season. This can also help identify areas that should be surveyed for current wintering habitat. Scale: Regional to rangewide dependent on availability of specimens. Target Initiation Date: 1996. Time Frame: Comparison of museum specimens 6 months - 1 year.
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.
BEHAVIORAL
13. Need: Food resources are a vital component of willow flycatcher habitat, both for maintenance of breeding individuals and for provisioning of young. The willow flycatcher is an aerial insectivore. Its use of habitat may be strongly influenced by availability of prey. Invertebrate composition is influenced by the vegetation and hydrologic characteristics of local habitat. Currently, we know very little about the composition of willow flycatcher prey nor patterns of prey availability. Task: Determine prey selection by flycatchers and prey abundance including seasonal patterns. Scale: Multiple sites within region or throughout range. Target Initiation Date: 1997. Duration of Study: At least 1 to 2 years per site.
MANAGEMENT
14. Need: Management of southwestern willow flycatcher populations requires and understanding of real and potential threats, particularly to flycatcher productivity. If productivity falls below a certain threshold, the population will not be maintained over time. In many areas, nest failure is one of the major factors influencing productivity of breeding songbirds. Causes and patterns of nest failure vary spatially and temporally, and long-term patterns may be important. Data on predation is needed from a larger sample of breeding populations in order to assess its effects on productivity rangewide. Task: Determine causes of nest failure to evaluate spatial and temporal patterns of predation and their effects on productivity. Scale: All data collected locally and aggregated at regional scales. Target Initiation Date: on-going. Duration of Study: 2 to 5 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.
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