Empidonax occidentalis - Nelson, 1897
Cordilleran Flycatcher
Other English Common Names: Cordilleran flycatcher
Taxonomic Status: Accepted
Related ITIS Name(s): Empidonax occidentalis Nelson, 1897 (TSN 554255)
French Common Names: Moucherolle des ravins
Spanish Common Names: Mosquero Barranqueño
Unique Identifier: ELEMENT_GLOBAL.2.100103
Element Code: ABPAE33160
Informal Taxonomy: Animals, Vertebrates - Birds - Perching Birds
 
Kingdom Phylum Class Order Family Genus
Animalia Craniata Aves Passeriformes Tyrannidae Empidonax
Genus Size: C - Small genus (6-20 species)
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Concept Reference
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Concept Reference: American Ornithologists' Union (AOU). 1998. Check-list of North American birds. Seventh edition. American Ornithologists' Union, Washington, D.C. [as modified by subsequent supplements and corrections published in The Auk]. Also available online: http://www.aou.org/.
Concept Reference Code: B98AOU01NAUS
Name Used in Concept Reference: Empidonax occidentalis
Taxonomic Comments: Formerly considered conspecific with E. difficilis (AOU 1989, 1998). Referred to as E. D. hellmayri by Johnson and Martin (1988). Johnson and Marten (1988) examined variation in the E. difficilis group and concluded that E. difficilis and E. occidentalis are distinct species. Phillips (1994) argued that existing information does not justify the recognition of E. occidentalis and E. difficilis as distinct species. Johnson (1994) provided additional analyses indicating that E. difficilis and E. occidentalis warrant separate-species status. Constitutes a superspecies with E. difficilis and E. flavescens (AOU 1998).
Conservation Status
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NatureServe Status

Global Status: G5
Global Status Last Reviewed: 07Apr2016
Global Status Last Changed: 02Dec1996
Ranking Methodology Used: Ranked by inspection
Rounded Global Status: G5 - Secure
Nation: United States
National Status: N5B (19Mar1997)
Nation: Canada
National Status: N4B,NUM (08Jan2018)

U.S. & Canada State/Province Status
Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
United States Arizona (S2S4B), California (SNR), Colorado (S5B), Idaho (S5B), Kansas (SNA), Montana (S4B), Navajo Nation (S4S5B), Nebraska (S1), Nevada (S5B), New Mexico (S5B,S4N), Oregon (S3?B), South Dakota (S5B), Texas (S3B), Utah (S3S4B), Washington (S3?B), Wyoming (S4B)
Canada Alberta (SUB), British Columbia (SU)

Other Statuses

IUCN Red List Category: LC - Least concern

NatureServe Global Conservation Status Factors

Range Extent Comments: BREEDING: southeastern Washington, southwestern Alberta, northern Idaho, western Montana, Wyoming, and western South Dakota south (generally east of Cascades and Sierra Nevada) to northern California, Nevada, and central and southeastern Arizona, and in Mexican highlands to Oaxaca (west of Isthmus of Tehuantepec), Puebla, and west-central Veracruz, and east to western Nebraska (rarely), central Colorado, central New Mexico, and western Texas (AOU 1989). Centers of abundance occur in Arizona, New Mexico, Colorado, central Utah, the Black Hills region of South Dakota, and northern Idaho (Sauer et al. 1997). NON-BREEDING: southern Baja California, and northern Mexico (casually to central California and southern Arizona) south through breeding range, occurring also in lowland areas south to Isthmus of Tehuantepec; reports from Chiapas, Guatemala, and Honduras are based on E. FLAVESCENS (AOU 1989). Casual in migration in Tres Marias Islands (off Nayarit), eastern New Mexico, and southwestern Kansas (AOU 1989).

Overall Threat Impact Comments: Threats to the species are largely unstudied. Habitat degradation from timber harvesting, heavy grazing, or development are possible threats. Relatively tolerant of human presence around nests, but may be vulnerable to disturbance just prior to fledging (USDA Forest Service 1994). BROOD PARASITISM: Considered a rare host for brown-headed cowbirds (MOLOTHRUS ATER; Ehrlich et al. 1988), but may be more vulnerable to parasitism if habitat is fragmented and edge that favors cowbirds is increased (USDA Forest Service 1994). In Montana, 5 of 12 nests observed were parasitized; eggs were damaged, most likely by pecking by the cowbird chick (Dolan and Wright 1984).

Short-term Trend Comments: Range-wide, populations appear to be relatively stable, but data are limited. North American Breeding Bird Survey (BBS) data show a non-significant survey-wide population increase from 1966 to 1996 (0.6 percent average annual increase; P = 0.67; N = 116 routes) and a non-significant decline from 1980 to 1996 (-0.4 percent average annual decline; P = 0.81; N = 106 routes). Thirty-year trend estimates for state and physiographic regions are not statistically significant, although possible declines occurred in Utah, the Southern Rockies and Central Rockies. Mapped 30-year trends show declines in the central Rockies, and increases in the southern and northern Rockies. Trend estimates for the more recent period of 1980 to 1996 show significant declines in the Southern Rockies and Pinyon-Juniper Woodland physiographic regions (-4.2 percent, P = 0.12, N = 29; and -1.4 percent, P = 0.10, N = 25 respectively). Although relative abundances average 0.49 to 1.82 birds per 25-mile survey route, the species is not detected on enough survey routes to provide a strong data set for trend analysis.

Other NatureServe Conservation Status Information

Distribution
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Global Range: BREEDING: southeastern Washington, southwestern Alberta, northern Idaho, western Montana, Wyoming, and western South Dakota south (generally east of Cascades and Sierra Nevada) to northern California, Nevada, and central and southeastern Arizona, and in Mexican highlands to Oaxaca (west of Isthmus of Tehuantepec), Puebla, and west-central Veracruz, and east to western Nebraska (rarely), central Colorado, central New Mexico, and western Texas (AOU 1989). Centers of abundance occur in Arizona, New Mexico, Colorado, central Utah, the Black Hills region of South Dakota, and northern Idaho (Sauer et al. 1997). NON-BREEDING: southern Baja California, and northern Mexico (casually to central California and southern Arizona) south through breeding range, occurring also in lowland areas south to Isthmus of Tehuantepec; reports from Chiapas, Guatemala, and Honduras are based on E. FLAVESCENS (AOU 1989). Casual in migration in Tres Marias Islands (off Nayarit), eastern New Mexico, and southwestern Kansas (AOU 1989).

U.S. States and Canadian Provinces

Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
Color legend for Distribution Map
NOTE: The maps for birds represent the breeding status by state and province. In some jurisdictions, the subnational statuses for common species have not been assessed and the status is shown as not-assessed (SNR). In some jurisdictions, the subnational status refers to the status as a non-breeder; these errors will be corrected in future versions of these maps. A species is not shown in a jurisdiction if it is not known to breed in the jurisdiction or if it occurs only accidentally or casually in the jurisdiction. Thus, the species may occur in a jurisdiction as a seasonal non-breeding resident or as a migratory transient but this will not be indicated on these maps. See other maps on this web site that depict the Western Hemisphere ranges of these species at all seasons of the year.
Endemism: occurs (regularly, as a native taxon) in multiple nations

U.S. & Canada State/Province Distribution
United States AZ, CA, CO, ID, KS, MT, NE, NM, NN, NV, OR, SD, TX, UT, WA, WY
Canada AB, BC

Range Map
Note: Range depicted for New World only. The scale of the maps may cause narrow coastal ranges or ranges on small islands not to appear. Not all vagrant or small disjunct occurrences are depicted. For migratory birds, some individuals occur outside of the passage migrant range depicted. For information on how to obtain shapefiles of species ranges see our Species Mapping pages at www.natureserve.org/conservation-tools/data-maps-tools.

Range Map Compilers: NatureServe, 2002


U.S. Distribution by County Help
State County Name (FIPS Code)
NE Dawes (31045), Sioux (31165)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
10 Hat (10120108)+, Upper White (10140201)+
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
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Basic Description: A small bird (flycatcher).
Reproduction Comments: Egg dates: June-July in Colorado, July in Montana (Johnsgard 1986). Incubation 14-15 days, by female along; young fledge after 14-18 days, fed by parents another 10-11 days (Baicich and Harrison 1997).
Ecology Comments: Rich (1999) found significant correlations between the relative abundance of cordilleran flycatcher and the abundance of warbling vireo (VIREO GILVUS), red-naped sapsucker (SPHYRAPICUS NUCHALIS), and Lincoln's sparrow (MELOSPIZA LINCOLNII), which tend to occur in similar habitats. There were weaker but significant associations with blue grosbeak (GUIRACA CAERULEA), house wren (TROGLODYTES AEDON), Bell's vireo (VIREO BELLII), and Lucy's warbler (VERMIVORA LUCIAE).
Non-Migrant: N
Locally Migrant: N
Long Distance Migrant: Y
Mobility and Migration Comments: Most arrive in central Colorado late in May (some as early as April), depart by late September; present in Montana usually late May-August (Niedrach and Rockwell 1939, Johnsgard 1986).
Palustrine Habitat(s): Riparian
Terrestrial Habitat(s): Cliff, Forest - Conifer, Forest - Hardwood, Forest - Mixed, Woodland - Conifer, Woodland - Hardwood, Woodland - Mixed
Habitat Comments: BREEDING: A riparian-dependent species that uses understory and mid-story vegetation layers (Rich 1999). Habitat is typically near a water source and well-shaded by tall trees or steep canyon walls (AOU 1989, USDA Forest Service 1994). Ranges from riparian woodlands through aspens into coniferous forest zones; extends out into sagebrush during nonbreeding season (Johnsgard 1986).

Breeds in shaded woodlands along stream corridors or moist ravines in coniferous forest, dense second-growth, aspen, and riparian woodlands, in foothills and mountain slopes; may also be found in similar types in suburban settings (Dobkin 1994, Baicich and Harrison 1997). Commonly associated with lodgepole pine (PINUS CONTORTA) forest and mixed conifer forest dominated by Douglas-fir (Hejl et al. 1995). In the Northern Rockies, depends heavily on riparian corridors and is relatively restricted to riparian bottomlands and adjacent conifer forests. It is more likely to be found in areas with greater numbers of snags, and is most frequently detected in cottonwood stands, but also in wetland, riparian shrub, Douglas-fir, cedar/grand fir (THUJA/ABIES GRANDIS), and spruce/fir (PICEA/ABIES) habitats (Hutto and Young 1999). On the Colorado Front Range, it shows a preference for Douglas-fir over other forest types; also occurs in aspen/willow (POPULUS/SALIX), ponderosa pine (PINUS PONDEROSA), and mixed forest stands (Winternitz 1976). In northern Arizona, it favors Ponderosa pine-Gambel oak stands (PINUS PONDEROSA/QUERCUS GAMBELII) over pine stands (Rosenstock 1998), and the species reaches higher densities in stands with high pine density and moderate understory oak density (Brawn and Balda 1988). In Mexico, breeds in humid to semiarid evergreen and pine-oak forest and cloud forest, often in shady arroyos; usually seen in shady understory, rarely in open areas except during migration (Howell and Webb 1995, Howell and Cannings 1992).

Constructs a cup nest in fork of a sapling or shrub, or typically against a flat surface such as in a cavity of a small tree, on a rocky ledge, in low dirt bank by stream, also among tangled tree roots, in mouths of mine tunnels, or in protected spots around buildings; nests commonly around mountain cabins (Niedrach and Rockwell 1939, Dobkin 1994, Howell and Webb 1995, Baicich and Harrison 1997).

NON-BREEDING: In winter, mostly occurs in mixed woodland and forest (Subtropical and Temperate zones). In Mexico, moves out of coniferous zones in winter (Howell and Webb 1995). In western Mexico, favors tropical deciduous forest, also occurs in second growth deciduous forest, cloud forest, and very occasionally recorded in pine-oak-fir forest (Hutto 1992).

Adult Food Habits: Invertivore
Immature Food Habits: Invertivore
Food Comments: Feeds on insects, also berries and occasionally seeds (Ehrlich et al. 1988). Most often hawks aerial insects, but also gleans insects from foliage and off the ground (USDA Forest Service 1994). In a Colorado study, Lepidoptera made up 61 percent of diet by dry weight, also consumed Coleoptera, Diptera, and Hymenoptera (Beaver and Baldwin 1975).
Adult Phenology: Diurnal
Immature Phenology: Diurnal
Economic Attributes Not yet assessed
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Management Summary
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Stewardship Overview: A bird of moist forests, montane riparian areas, and shady ravines. Formerly considered the same species as Pacific-slope flycatcher (EMPIDONAX DIFFICILIS), and together were known as the western flycatcher. The species were split in 1989 based on voice, allozyme differences, and lack of interbreeding where ranges overlap (Johnson and Marten 1988, AOU 1989, Johnson 1994). Differences in life history between the two species have not been explored. Cordilleran populations appear generally stable, although recent declines are evident in southern parts of range. Further monitoring and study are needed to better understand its status.
Restoration Potential: Still a relatively common species. Should benefit from forest and riparian management that maintains stands with shrub and sapling understories, snags, and intact streambanks.
Preserve Selection & Design Considerations: There is little known about landscape relationships. In a study in a northwestern California Douglas-fir forest, western flycatcher (EMPIDONAX DIFFICILIS) avoided edges, yet did not respond negatively to forest fragmentation. Positive association to the proximity and length of clearcut edges and positively correlated with stands that were more insular, or contained more clearcuts and total edge (Rosenberg and Raphael 1986). Given cordilleran's association with riparian habitats throughout most of its range, the species may be adapted to patchier habitats, but its relationships to area, surrounding landscapes, and types of edge need to be further studied.
Management Requirements: Should benefit from maintaining moist montane riparian and forest habitats with moderate to dense canopies, shrub or sapling understories, snags, and intact streambanks, especially in mountain ravines and canyons. Overall, there is little specific information available on the effects of human activities and habitat alterations on this species. Until recently, many management studies overlooked EMPIDONAX flycatchers or lumped them together due to the difficulty of distinguishing this suite of species. Recent breeding bird studies that use trained observers more often detect cordilleran flycatcher, but information on management requirements for the species is still slim. There is a large body of literature, however, on human impacts on riparian habitats which can provide direction for maintaining the integrity of these ecosystems. For example, see Ohmart (1994) or Ohmart and Anderson (1986) for general overviews, and Idaho Partners in Flight (1998) for riparian habitat management guidelines.

TIMBER HARVEST: Harvesting in riparian corridors could be detrimental, and leaving a buffer between riparian habitats and harvest units would likely benefit the species. A summary of silvicultural studies suggests that abundances are similar in partially cut forests and in uncut forests (Hejl et al. 1995). A number of studies, however, show declines with more extensive timber harvest. In an Arizona mixed coniferous forest, for example, density declined 50 percent four years after timber harvest (most noticeably on south aspects) where the prescription included a mix of individual tree selection, group selection to reduce basal area 30 percent, and clearcut patches, but left steep slopes unharvested (Scott and Gottfried 1983). In northern Arizona ponderosa pine, uncut stands or moderately thinned stands over severely thinned stands (Szaro and Balda 1979, Brawn and Balda 1988). In the Northern Rockies, it is more likely to occur in areas with greater numbers of snags (Hutto and Young 1999). In northwestern California, observations of western flycatcher (E. DIFFICILIS or OCCIDENTALIS unknown) in a mixed forest dominated by Douglas-fir (PSEUDOTSUGA MENZIESII) and ponderosa pine (PINUS PONDEROSA) showed that density declined an average 80 percent where overstory removal reduced total tree density by 75 percent and basal area by 80 percent (Franzreb and Ohmart 1978). In western Mexico tropical deciduous forest, abundance was significantly and dramatically less in short second-growth that had been deforested for livestock production than in undisturbed forest, and somewhat less abundant in tall second-growth than in undisturbed forest (Hutto 1992).

Studies of Pacific-slope flycatcher (EMPIDONAX DIFFICILIS) show the species prefers old forests over younger stands (Raphael et al. 1988, Carey et al. 1991, Manuwal 1991). In an Oregon Cascades study, the species favored old stands and areas with decayed logs, fern and deciduous shrub cover, western hemlocks (TSUGA HETEROPHYLLA) and very large western redcedar (THUJA PLICATA); the authors suggested that older stands probably best meet the species need for open flying space for feeding (Gilbert and Allwine 1991). In mature, unmanaged forest stands, average abundances are slightly higher along streamsides than in upslope stands, but not significantly so (McGarigal and McComb 1992). These associations need to be examined for the cordilleran flycatcher as well.

GRAZING: Overgrazing can cause heavy damage to the understory of riparian habitats and delay regeneration (Ohmart 1994), which would eliminate the habitat. Often nests in low streambanks, so nesting habitat can be destroyed when livestock are allowed to break down streambanks and nests may be vulnerable to trampling (Hutto and Young 1999). Livestock presence may also encourage brown-headed cowbirds (MOLOTHRUS ATER), a brood parasite.

Monitoring Requirements: Can be detected with standard monitoring methods. Specialized monitoring may be needed for adequate samples. Is recorded on BBS, but more targeted monitoring for the species would provide more accurate information (Saab and Rich 1997, Hutto and Young 1999). See Rich (1999) for guidelines on assessing the occurrence of breeding birds in riparian habitats.
Management Research Needs: More study is needed of the effects of timber harvest, grazing, and other habitat alterations, particularly in relationship to productivity and survivorship. Winter ecology, habitat preferences, and threats need investigation. Examination of area requirements, effects of fragmentation, spatial juxtaposition of habitat other aspects of landscape ecology are needed. Further study of brood parasitism rates in relation to human alterations of habitat and behavioral response to parasitism is needed.
Biological Research Needs: Most aspects of demographics, life history, and ecology need better study given the recent split between cordilleran and Pacific-slope flycatcher. Need information on details of habitat relationships; wintering ecology; migratory patterns and location of wintering grounds for migratory populations; survivorship; diet, nutrition and energetics; disease, nest predation and other sources of mortality; rates of and response to brood parasitism; site fidelity; territory size; limiting factors. Need information on breeding biology; wintering ecology; migratory patterns and location of wintering grounds for migratory populations; life span and survivorship; physiology; diet, nutrition and energetics; disease, nest predation and other sources of mortality; rates of and response to brood parasitism; philopatry, territory size; details of habitat relationships; limiting factors.
Population/Occurrence Delineation
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Group Name: Passerines

Use Class: Breeding
Subtype(s): Foraging Area, Nest Site, Nesting Colony
Minimum Criteria for an Occurrence: Evidence of historical breeding, or current and likely recurring breeding, at a given location, minimally a reliable observation of one or more breeding pairs in appropriate habitat. Be cautious about creating EOs for observations that may represent single breeding events outside the normal breeding distribution.

Mapping Guidance: Breeding occurrences include nesting areas as well as foraging areas.

For swallows and other species that have separate nesting and foraging areas, separations are based on nest sites or nesting areas, not to locations of foraging individuals. For example, nesting areas separated by a gap larger than the separation distance are different occurrences, regardless of the foraging locations of individuals from those nesting areas. This separation procedure is appropriate because nesting areas are the critical aspect of swallow breeding occurrences, tend to be relatively stable or at least somwhat predictable in general location, and so are the basis for effective conservation; foraging areas are much more flexible and not necessarily static.

Separation Distance for Unsuitable Habitat: 5 km
Separation Distance for Suitable Habitat: 5 km
Separation Justification: Significant dispersal and associated high potential for gene flow among populations of birds separated by tens of kilometers (e.g., Moore and Dolbeer 1989), and increasing evidence that individuals leave their usual home range to engage in extrapair copulations, as well as long foraging excursions of some species, make it difficult to circumscribe occurrences on the basis of meaningful population units without occurrences becoming too large. Hence, a moderate, standardized separation distance has been adopted for songbirds and flycatchers; it should yield occurrences that are not too spatially expansive while also accounting for the likelihood of gene flow among populations within a few kilometers of each other.

Be careful not to separate a population's nesting areas and foraging areas as different occurrences; include them in the same occurrence even if they are more than 5 km apart. Mean foraging radius (from nesting area) of Brown-headed Cowbird females was 4.0 kilometers in California, 1.2 kilometers in Illinois-Missouri (Thompson 1994). Yellow-headed Blackbirds, Brewer's Blackbirds, and probably Red-winged Blackbirds all forage up to 1.6 kilometers away from breeding colony (Willson 1966, Horn 1968). In one study, Brewer's Blackbirds were found as far as 10 kilometers from nesting area (Williams 1952), but this may be unusual.

For swallows and other parrerines with similar behavioral ecology, separation distance pertains to nest sites or nesting colonies, not to locations of foraging individuals. For example, nesting areas separated by a gap of more than 5 km are different occurrences, regardless of the foraging locations of individuals from those nesting areas. This separation procedure is appropriate because nesting areas are the critical aspect of swallow breeding occurrences, tend to be relatively stable or at least somwhat predictable in general location, and so are the basis for effective conservation; foraging areas are much more flexible and not necessarily static.

Be cautious about creating EOs for observations that may represent single breeding events outside the normal breeding distribution.

Unsuitable habitat: Habitat not normally used for breeding/feeding by a particular species. For example, unsuitable habitat for grassland and shrubland birds includes forest/woodland, urban/suburban, and aquatic habitats. Most habitats would be suitable for birds with versatile foraging habits (e.g., most corvids).

Date: 10Sep2004
Author: Hammerson, G.

Use Class: Migratory stopover
Subtype(s): Foraging Area, Roost Site
Minimum Criteria for an Occurrence: For most passerines: Evidence of recurring presence of migrating individuals (including historical) and potential recurring presence at a given location; minimally a reliable observation of 25 birds in appropriate habitat.

For swallows: Evidence of recurring presence of migrating flocks (including historical) and potential recurring presence at a given location; minimally a reliable observation of 100 birds in appropriate habitat (e.g., traditional roost sites).

Occurrences should be locations where the species is resident for some time during the appropriate season; it is preferable to have observations documenting presence over at least 7 days annually.

EOs should not be described for species that are nomadic during nonbreeding season: e.g., Lark Bunting.

Be cautious about creating EOs for observations that may represent single events.

Separation Distance for Unsuitable Habitat: 5 km
Separation Distance for Suitable Habitat: 5 km
Separation Justification: Separation distance somewhat arbitrary but intended to define occurrences of managable size for conservation purposes. Occurrences defined primarily on the basis of areas supporting concentrations of birds, rather than on the basis of distinct populations.

For swallows and other species with similar behavioral ecology, the separation distance pertains to communal roost sites rather than to foraging areas; the former tend to be more stable and specific over time than the latter.

Date: 03Sep2004
Author: Hammerson, G., and S. Cannings

Use Class: Nonbreeding
Subtype(s): Foraging Area, Roost Site
Minimum Criteria for an Occurrence: Any area used traditionally in the nonbreeding season (used for populations that are not resident in a location year-round). Minimally, reliable observations of 10 or more individuals in appropriate habitat for 20 or more days at a time. For G1-G3 species, observations of fewer individuals could constitute an occurrence of conservation value. Sites used during migration should be documented under the 'migratory stopover' location use class.

Separation Distance for Unsuitable Habitat: 5 km
Separation Distance for Suitable Habitat: 5 km
Separation Justification: Separation distance is necessarily arbitrary but attempts to balance the high mobility of birds with the need for occurrences of reasonable spatial scope. Note that a population's roost sites and foraging areas are parts of the same occurrence, even if they are more than 5 km apart.

For swallows and other species with similar behavioral ecology, the separation distance pertains to communal roost sites rather than to foraging areas; the former tend to be more stable and specific over time than the latter.

Date: 03Sep2004
Author: Hammerson, G.

Use Class: Nonmigratory
Minimum Criteria for an Occurrence: Occurrences are based on evidence of historical presence, or current and likely recurring presence, at a particular location. Such evidence minimally includes collection or reliable observation and documentation of one or more individuals in or near appropriate habitat.

These occurrence specifications are used for nonmigratory populations of passerine birds.

Separation Barriers: None.
Separation Distance for Unsuitable Habitat: 5 km
Separation Distance for Suitable Habitat: 5 km
Separation Justification: Significant dispersal and associated high potential for gene flow among populations of birds separated by tens of kilometers (e.g., Moore and Dolbeer 1989), and increasing evidence that individuals leave their usual home range to engage in extrapair copulations, as well as long foraging excursions of some species, make it difficult to circumscribe occurrences on the basis of meaningful population units without occurrences becoming too large. Hence, a moderate, standardized separation distance has been adopted for songbirds and flycatchers; it should yield occurrences that are not too spatially expansive while also accounting for the likelihood of gene flow among populations within a few kilometers of each other.

Be careful not to separate a population's nesting areas and breeding-season foraging areas as different occurrences; include them in the same occurrence even if they are more than 5 km apart. Blue jays have small summer home ranges but fly up to 4 kilometers to harvest mast (Tarvin and Woolfenden 1999). Flocks of pinyon jays range over 21-29 square kilometers (Ligon 1971, Balda and Bateman 1971); nesting and foraging areas may be widely separated. Tricolored blackbirds forage in flocks that range widely to more than 15 kilometers from the nesting colony (Beedy and Hamilton 1999).

Unsuitable habitat: Habitat not normally used for breeding/feeding by a particular species. For example, unsuitable habitat for grassland and shrubland birds includes forest/woodland, urban/suburban, and aquatic habitats. Most habitats would be suitable for birds with versatile foraging habits (e.g., most corvids).

Date: 10Sep2004
Author: Hammerson, G.
Notes: These specs pertain to nonmigratory species.
Population/Occurrence Viability
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U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
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Authors/Contributors
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Management Information Edition Date: 08Sep1999
Management Information Edition Author: PAIGE, C.; REVISIONS BY M. KOENEN AND D.W. MEHLMAN
Management Information Acknowledgments: Support for the preparation of this abstract was provided by the National Fish and Wildlife Foundation's Neotropical Migratory Bird Conservation Initiative, through challenge grant number 97-270 to The Nature Conservancy, Wings of the Americas Program. Matching funds for this grant were donated by Canon U.S.A., Inc.
Element Ecology & Life History Edition Date: 13Jan1995
Element Ecology & Life History Author(s): Hammerson, G.

Zoological data developed by NatureServe and its network of natural heritage programs (see Local Programs) and other contributors and cooperators (see Sources).

References
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  • Allen, C. R., S. Demarais, and R. S. Lutz. 1994. Red imported fire ant impact on wildlife: an overview. The Texas Journal of Science 46(1):51-59.

  • American Ornithologists' Union (AOU). 1989. Thirty-seventh supplement to the American Ornithologists' Union Checklist of North American birds. Auk 106:532-538.

  • American Ornithologists' Union (AOU). 1998. Check-list of North American birds. Seventh edition. American Ornithologists' Union, Washington, D.C. [as modified by subsequent supplements and corrections published in The Auk]. Also available online: http://www.aou.org/.

  • Andrews, R. R. and R. R. Righter. 1992. Colorado Birds. Denver Museum of Natural History, Denver. 442 pp.

  • Baicich, P. J., and C. J. O. Harrison. 1997. A guide to the nests, eggs and nestlings of North American birds. Second edition. Academic Press, New York.

  • Balda, R. P., and G. C. Bateman. 1971. Flocking and annual cycle of the piñon jay, Gymnorhinus cyanocephalus. Condor 73:287-302.

  • Beaver, D.L. and P.H. Baldwin. 1975. Ecological overlap and the problem of competition and sympatry in the western and Hammond's flycatchers. Condor 77:1-13.

  • BirdLife International. 2004b. Threatened birds of the world 2004. CD ROM. BirdLife International, Cambridge, UK.

  • Brawn, J.D., and R.P. Balda. 1988. The influence of silvicultural activity on ponderosa pine forest bird communities in the southwestern United States. Pages 3-21 in J.A. Jackson, editor. Bird Conservation 3. University of Wisconsin Press, Madison, WI.

  • Campbell, R.W., N.K. Dawe, I. McTaggart-Cowan, J.M. Cooper, G.W. Kaiser, M.C.E. McNall and G.E.J. Smith 1997. The Birds of British Columbia, Vol. 3, Passerines: Flycatchers through Vireos. UBC Press in cooperation with Environ. Can., Can. Wildl. Serv. and B.C. Minist. Environ., Lands and Parks, Wildl. Branch. 700pp.

  • Cannings, R.J. 1998. The Birds of British Columbia - a taxonomic catalogue. B.C. Minist. Environ., Lands and Parks, Wildl. Branch, Victoria, Wildl. Bull. B-86. 266pp.

  • Carey, A.B., M.M. Hardt, S.P. Horton, and B.L. Biswell. 1991. Spring bird communities in the Oregon Coast Range. Pages 123-142 in L.F. Ruggiero, K.B. Aubry, A.B. Carey, and M.H. Huff, technical coordinators. Wildlife and Vegetation of unmanaged Douglas-fir Forests. USDA Forest Service, Pacific Northwest Research Station, General Technical Report PNW-GTR-285, Portland, OR.

  • Dobkin, D.S. 1994. Conservation and management of neotropical migrant landbirds in the Northern Rockies and Great Plains. University of Idaho Press, Moscow, ID.

  • Dolan, P. M. and P. L. Wright. 1984. Damaged western flycatcher eggs in nests containing brown-headed cowbird chicks. Condor (86):483-485.

  • Dorn, Jane L. and R.D. Dorn. 1990. Wyoming Birds. Mountain West Publishing, Cheyenne.

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