Vireo vicinior - Coues, 1866
Gray Vireo
Other English Common Names: gray vireo
Taxonomic Status: Accepted
Related ITIS Name(s): Vireo vicinior Coues, 1866 (TSN 179008)
French Common Names: Viréo gris
Spanish Common Names: Vireo Gris
Unique Identifier: ELEMENT_GLOBAL.2.101771
Element Code: ABPBW01140
Informal Taxonomy: Animals, Vertebrates - Birds - Perching Birds
 
Kingdom Phylum Class Order Family Genus
Animalia Craniata Aves Passeriformes Vireonidae Vireo
Genus Size: D - Medium to large genus (21+ 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: Vireo vicinior
Taxonomic Comments: See Johnson et al. (1988) and Murray et al. (1994) for analyses of the phylogenetic relationships among vireos.
Conservation Status
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NatureServe Status

Global Status: G5
Global Status Last Reviewed: 12Aug2015
Global Status Last Changed: 12Aug2015
Ranking Methodology Used: Ranked by calculator
Rounded Global Status: G5 - Secure
Reasons: Fairly large range in southwestern United States and northwestern Mexico; population size estimated at around 400,000; apparently stable or perhaps slowly increasing; no major threats, but potentially/locally affected by livestock grazing, changes in fire regime, and cowbird parasitism; breeding range is projected to increase with ongoing climate change.
Nation: United States
National Status: N5B (12Aug2015)

U.S. & Canada State/Province Status
United States Arizona (S4), California (S2), Colorado (S2B), Navajo Nation (S4B), Nevada (S3B), New Mexico (S4B,S3N), Texas (S4B), Utah (S3?B)

Other Statuses

IUCN Red List Category: LC - Least concern

NatureServe Global Conservation Status Factors

Range Extent: 20,000-2,500,000 square km (about 8000-1,000,000 square miles)
Range Extent Comments: This species breeds lfrom southern California, southern Nevada, central Utah, southwestern and southeastern Colorado, and north-central New Mexico south to northwestern Baja California, southeastern Arizona, southeastern New Mexico, western Texas, and northwestern Coahuila (AOU 1998; C. Rustay, pers. comm.). Center of abundance during the breeding season, based on North American Breeding Bird Survey (BBS), is in northern Arizona and southern Utah (Sauer et al. 1997). Nonbreeding range includes central and southern Baja California, southwestern Arizona (rarely), Sonora (including Tiburón and San Esteban islands), and (rarely) western Texas (Big Bend region) (AOU 1998). Winter range extent is smaller than breeding range extent.

Number of Occurrences:  
Number of Occurrences Comments: Number of distinct occurrences has not been determined using standardized criteria, but this species is represented by a large number of recent observation sites (e.g., see eBird data) and locations (as defined by IUCN).

Population Size: 100,000 - 1,000,000 individuals
Population Size Comments: Total adult population size is uncertain but relatively large. Partners in Flight (2013) estimated global population size at 400,000.

Overall Threat Impact: Low
Overall Threat Impact Comments: Pinyon-juniper woodland habitat of this species is subject to grazing and clearing to increase grassland (livestock grazing habitat), mesquite and desert scrub habitats are grazed and cleared for development, and chaparral habitats have undergone extensive conversion in urban areas of southern California. 

Habitat fragmentation or the presence of livestock may facilitate brown-headed cowbird brood parasitism and presumably are detrimental (USDA Forest Service 1994). This species is regarded as a common host for the cowbird, but rates of parasitism and impacts on productivity are unknown. Some authors have suggested that declines in California and Arizona resulted from brood parasitism (DeSante and George 1994) as the cowbird was originally limited to the Great Plains until it expanded west with the spread of domestic livestock. However, Breeding Bird Survey data (increasing trend) suggest that gray viroes are not now being detrimentally affected by cowbird parasitism to any significant degree.

This species may be negatively affected by livestock grazing where shrub cover is diminished or removed. Wauer (1977) noted that gray vireo abundance increased after grazing ceased and woody plants gradually increased in Big Bend National Park. On the other hand, the species may benefit to some degree from increases in arid scrubland resulting from overgrazing of livestock in areas previously dominated by grasslands (Raitt and Pimm 1978).

Changes in fire regime that bring about an increase in fire extent or frequency may be detrimental by reducing or degrading habitat (USDA Forest Service 1994). Such changes potentially may result from ongoing climate change and other factors.

According to van Riper et al. (2014), the breeding range is projected to increase by 58-71 percent between 2010 and 2099 as a result of ongoing climate.

Short-term Trend: Relatively Stable (<=10% change)
Short-term Trend Comments: Breeding Bird Survey (BBS) data for 2003-2013 indicate a relatively stable or slowly increasing trend. However, the species was recorded at a low abundance level (average of fewer than 1 bird per route), so the results must be intepreted with caution.

Long-term Trend: Decline of <30% to relatively stable
Long-term Trend Comments: Long-term trend (past 200 years) is uncertain, but distribution and abundance likely declined to a small degree as a result of habitat changes. North American Breeding Bird Survey (BBS) data indicate that survey-wide trend over the past several decades was relatively stable or slowly increasing. However, the species was recorded at a low abundance level (average of fewer than 1 bird per route), so the results must be intepreted with caution.

Other NatureServe Conservation Status Information

Distribution
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Global Range: (20,000-2,500,000 square km (about 8000-1,000,000 square miles)) This species breeds lfrom southern California, southern Nevada, central Utah, southwestern and southeastern Colorado, and north-central New Mexico south to northwestern Baja California, southeastern Arizona, southeastern New Mexico, western Texas, and northwestern Coahuila (AOU 1998; C. Rustay, pers. comm.). Center of abundance during the breeding season, based on North American Breeding Bird Survey (BBS), is in northern Arizona and southern Utah (Sauer et al. 1997). Nonbreeding range includes central and southern Baja California, southwestern Arizona (rarely), Sonora (including Tiburón and San Esteban islands), and (rarely) western Texas (Big Bend region) (AOU 1998). Winter range extent is smaller than breeding range extent.

U.S. States and Canadian Provinces
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, NM, NN, NV, TX, UT

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)
AZ Apache (04001), Navajo (04017)
CA Inyo (06027)*, Kern (06029)*, San Bernardino (06071)
CO Delta (08029), Dolores (08033), Eagle (08037), Fremont (08043), Garfield (08045), Huerfano (08055)*, La Plata (08067), Las Animas (08071), Mesa (08077), Moffat (08081), Montezuma (08083), Montrose (08085), Otero (08089), Ouray (08091), Prowers (08099)*, Rio Blanco (08103), Routt (08107), San Miguel (08113)
NM Bernalillo (35001), Catron (35003), Chaves (35005), Dona Ana (35013), Eddy (35015), Hidalgo (35023)*, Mckinley (35031), Otero (35035), Rio Arriba (35039), San Juan (35045), San Miguel (35047), Sandoval (35043), Santa Fe (35049), Sierra (35051), Socorro (35053)
UT Washington (49053)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
11 Upper Arkansas (11020002)+, Upper Arkansas-Lake Meredith (11020005)+, Huerfano (11020006)+*, Upper Arkansas-John Martin (11020009)+*, Purgatoire (11020010)+, Upper Canadian (11080003)+, Upper Canadian-Ute Reservoir (11080006)+
13 Rio Grande-Santa Fe (13020201)+, Jemez (13020202)+, Rio Grande-Albuquerque (13020203)+, Rio Puerco (13020204)+, Arroyo Chico (13020205)+, Rio Salado (13020209)+, Jornada Del Muerto (13020210)+, Caballo (13030101)+, El Paso-Las Cruces (13030102)+, Tularosa Valley (13050003)+, Salt Basin (13050004)+, Pecos headwaters (13060001)+*, Rio Penasco (13060010)+, Upper Pecos-Black (13060011)+
14 Colorado headwaters (14010001)+, Colorado headwaters-Plateau (14010005)+, Lower Gunnison (14020005)+, Uncompahange (14020006)+, Westwater Canyon (14030001)+, Upper Dolores (14030002)+, San Miguel (14030003)+, Lower Dolores (14030004)+, Upper Green-Flaming Gorge Reservoir (14040106)+, Lower White (14050007)+, Upper San Juan (14080101)+, Animas (14080104)+, Middle San Juan (14080105)+, Mancos (14080107)+, Lower San Juan-Four Corners (14080201)+, Mcelmo (14080202)+, Montezuma (14080203)+, Chinle (14080204)+, Lower San Juan (14080205)+
15 Upper Virgin (15010008)+, Carrizo Wash (15020003)+, Polacca Wash (15020013)+, Jadito Wash (15020014)+, Moenkopi Wash (15020018)+, Piute Wash (15030102)+, Animas Valley (15040003)+*, San Francisco (15040004)+, San Bernardino Valley (15080302)+*
16 Ivanpah-Pahrump Valleys (16060015)+*
18 South Fork Kern (18030002)+*, Owens Lake (18090103)+*, Eureka-Saline Valleys (18090201)+*, Upper Amargosa (18090202)+*, Death Valley-Lower Amargosa (18090203)+*, Antelope-Fremont Valleys (18090206)+*, Mojave (18090208)+*, Southern Mojave (18100100)+*
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
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Basic Description: A small bird (vireo).
Reproduction Comments: Clutch size is 3-5 (usually 4; Bailey 1928; Terres 1980). Both sexes incubate and tend young; incubation takes 13-14 days; young fledge in 13-14 days (Ehrlich et al. 1988).
Ecology Comments: Territories observed by Barlow (1977) ranged from 2.4 to 8 hectares in the northern Chihuahuan Desert and in Yavapai County, central Arizona. Barlow (1997) noted a singing male every 300 meters over a distance of 15 kilometers.

May be a principle seed disperser for B. MICROPHYLLA, and the close overlap between their ranges suggests a possible mutualism (Bates 1992a). Feeds on its fruit which are available in quantity from September through April. Both males and females defend territories in winter, and individuals will return to the same winter territory in successive years; nine territories were 0.3-1.4 hectares (mean 0.9 hectares; Bates 1992b).

Non-Migrant: N
Locally Migrant: Y
Long Distance Migrant: Y
Mobility and Migration Comments: This species is mostly a short-distance migrant that cavates most of its breeding range for winter. It arrives in nesting areas in California in March; in Arizona and Texas usually in April (Terres 1980); moves out of northern Arizona by mid to late September; may arrive on wintering grounds as early as August 25 (Phillips et al. 1964). Winters from southwestern Arizona mountains into Mexico to southern Sonora and southern Baja California (Phillips et al. 1964). Several wintering individuals also confirmed in the Big Bend region, Texas (Barlow and Wauer 1971).
Terrestrial Habitat(s): Desert, Shrubland/chaparral, Woodland - Conifer, Woodland - Hardwood, Woodland - Mixed
Habitat Comments: Breeding habitats include warm/hot, semi-arid, shrubby habitats, especially mesquite and brushy pinyon-juniper woodlands; also chaparral and desert scrub. Thorn scrub, oak-juniper woodland, pinyon-juniper, juniper-cholla, mesquite, dry chaparral (Bent 1950, AOU 1983). Builds cup nest suspended from forked twig in a shrub or tree 0.5 to 2 meters tall (Ehrlich et al. 1988); nest usually 0.5-3.5 meters above ground.

In New Mexico, breeding occurs in rocky hills covered with sparse bushes and scrub, in juniper, hackberry (Celtis spp.) and Grave's oak (Q. gravesi; Bailey 1935, Barlow 1977). In northwestern New Mexico, found at elevations from 5800 - 7200 feet in broad-bottomed canyons (flat or gently sloped valleys) below or near ridge-top/rock outcrop/cliff head walls of canyons or gently sloped bowls in pinyon-juniper woodland (Reeves 1998). The pinyon-juniper is sometimes dense canopied woods and at other times widely-spaced trees creating parkland. Trees are generally mature ranging from 12 to 25 feett in height. Other shrubs species include Utah Serviceberry (Amelanchier utahensis) and Antelope brittlebrush (Purshia tridentata). There is often considerable bare soil between herbaceous plants forming ground cover. At the upper elevation, ponderosa pine (Pinus ponderosa) is sparsely situated among pinyons and junipers (Reeves 1998).

In Arizona, gray vireos frequent juniper (Juniperus spp.) habitats of Upper Sonoran Zone, also mesquite (Prosopis spp.); usually they prefer large juniper or chaparral with scattered trees (Phillips 1964). In southern Nevada, these birds occur in pinyon, juniper and sagebrush (Artemisia spp.) with additions of mountain mahogany (Cercocarpus ledifolius), Gambel oak (Quercus gambelii), Mexican manzanita (Arctostaphylos pungens), squaw apple (PERAPHYLLUM RAMOSISSIMUM), and cliffrose (COWANIA STANSBURYANA; Johnson 1972, cited in USDA Forest Service 1994). In Big Bend National Park, Texas, gray vireos occur in lower chaparral between 1219 and 1676 meters (4000 to 5500 feet elevation); they nest in Gregg's ash (FRAXINUS GREGGII) and evergreen sumac (RHUS VIRENS; Barlow 1977, Wauer 1977). In Joshua Tree National Monument and eastern Mojave Desert, California, they occurred in pinyon-juniper or pinyon-juniper mixed with sagebrush. In southern California (San Jacinto area), habitat includes chaparral dominated by chamise (ADENOSTOMA FASCICULATUM) or redshanks (A. SPARSIFOLIUM); also scrub oak, manzanita (ARCTOSTAPHYLOS spp.), CEONOTHUS, pinyon, and sagebrush. In Laguna Mountains, California, gray viroes were recorded in chamise and CEONOTHUS GREGGII (USDA Forest Service 1994).

In migration and winter, gray vireos occur in habitats to those used during the breeding season; also desert and arid scrub, chaparral, brushy scrub in pinyon-juniper woodland, semi-open areas with scattered scrub and semi-open arid brushland (AOU 1983, Terborgh 1989, Howell and Webb 1995). Winter range closely overlaps the range of one species of elephant tree, BURSERA MICROPHYLLA, throughout the coastal deserts surrounding the Gulf of California. A study in Sonora, Mexico, found heavy dependence on B. MICROPHYLLA fruits, which are available in quantity from September through April. Only one disjunct wintering population occurs outside the range of B. MICROPHYLLA (Bates 1992a), in the Chisos Mountains, Big Bend National Park, Texas, in habitat dominated by Texas persimmon (DIOSPYROS TEXANA) mixed with honey mesquite (PROSOPIS JULIFLORA), whitethorn acacia (ACACIA CONSTRICTA) and other shrubs (Barlow and Wauer 1971).

Adult Food Habits: Invertivore
Immature Food Habits: Invertivore
Food Comments: When breeding, feeds on insects (e.g., Orthoptera, Coleoptera; Terres 1980). Will sometimes scratch on ground like a towhee. Contents of two stomachs examined included caterpillars, a moth, a stink-bug (PRIONOSOMA PODOPIOIDES), a tree-hopper (PLATYCENTRUS ACUTICORNIS), a tree cricket (OECANTHUS), dobson flies (CHAULIODES), a cicada (TIBICINOIDES HESPERIUS), and a long-horned grasshopper (Chapin 1925, cited in Bent 1950). In winter in the coastal desert of Sonora, Mexico, feeds almost entirely on the fruit of one species of elephant tree (BURSERA MICROPHYLLA), although insects were also found in stomach contents (Bates 1992a).
Adult Phenology: Diurnal
Immature Phenology: Diurnal
Length: 14 centimeters
Weight: 13 grams
Economic Attributes Not yet assessed
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Management Summary
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Stewardship Overview: Poorly known, providing ample opportunity for amateur and professional naturalists to contribute to a better understanding of ecology and management needs. Has a relatively limited distribution and low abundance in the semi-arid shrublands of southwest uplands. It has apparently declined in California and Arizona, possibly due to cowbird brood parasitism. Loss of chaparral to development, clearing or grazing in pinyon-juniper woodlands, or other habitat changes on breeding or wintering grounds could be affecting the species, but impacts are entirely unstudied. Heavily dependent on the fruit of elephant trees (BURSERA MICROPHYLLA) during the winter.
Species Impacts: Impacts of the species are unknown. Elephant trees (B. MICROPHYLLA) may depend on gray vireo and only one or a few other bird species to disperse seeds.
Restoration Potential: The vireo and its principal habitats are still widely distributed throughout the southwest, so there is opportunity to conserve the species while it still occurs throughout most of its historic range. However, without better understanding the causes of decline, restoration solely though habitat protection may be fruitless, particularly if brood parasitism or large-scale cumulative changes are at play.
Preserve Selection & Design Considerations: Landscape use has not been examined, although in California it shows a preference for unbroken chaparral and does not favor edges (USDA Forest Service 1994). Barlow (1977) suggests that large tracts of undisturbed habitat are required to support individual pairs, given the size of territories he observed in Texas and Arizona. In addition, habitat fragmentation increases vulnerability to cowbird brood parasitism.
Management Requirements: Very little is known about management requirements or sensitivity to land management activities. Not all seemingly suitable habitat is occupied, and the details of habitat preferences are unstudied. Requires semi-arid shrub habitats, either extensive shrubland or scattered shrubs among pinyon-juniper woodlands. May prefer shrublands that are mature or late in post-fire succession (USDA Forest Service 1994). Shrub cover that creates a continuous layer of twig growth from 0.3 to 1.5 meters above the ground is a common habitat factor (Grinnell and Miller 1944, cited in USDA Forest Service 1994). In Arizona and Texas, territories were near a water supply available during at least part of the breeding season (Barlow 1977). However, in New Mexico, several populations are not near water sources and do not seem to require water (C. Rustay, pers. comm.). On wintering grounds in Sonora, Mexico, depends heavily on the fruits of elephant trees (BURSERA MICROPHYLLA; Bates 1992a) and could be affected by changes to this habitat. Prolonged drought and habitat clearing (e.g., for development or to increase pasture land) are detrimental (Barlow 1977).
Monitoring Requirements: A diurnal songbird with a distinctive and persistent song that can be monitored by standard point count or transect monitoring methods. Call note is unusual: a clear chatter (Phillips et al. 1964). The loud and persistent song, however, may cause observers to overestimate abundance (Grinnell and Swarth 1913, cited in USDA Forest Service 1994). May be more often heard than seen, preferring to remain at mid-levels in dense brush. Preference for steep slopes and dense, shrubby vegetation presents problems for access and can make sampling difficult, and it may not be accurately sampled from roads or trails (USDA Forest Service 1994). Its distribution is generally patchy and random sampling may not provide accurate information about abundance (USDA Forest Service 1994).
Management Research Needs: Information is needed on brood parasitism rates, behavioral response to parasitism, and its effects on productivity. Need more information on habitat use and an understanding of landscape relationships and effects of habitat fragmentation. Also need investigation of the effects of grazing, off-road recreation, and changes in fire regime, climate, or environmental contaminants. The species wintering ecology and threats or changes to BURSERA MICROPHYLLA habitats on winter grounds need study.
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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NatureServe Conservation Status Factors Edition Date: 12Aug2015
NatureServe Conservation Status Factors Author: Hammerson, G.
Management Information Edition Date: 30Sep1999
Management Information Edition Author: PAIGE, C.; REVISIONS BY M. KOENEN AND D.W. MEHLMAN
Management Information Acknowledgments: A critical and helpful review of this abstract was supplied by Chris Rustay. 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: 12Aug2015
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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  • American Ornithologists' Union (AOU). 1983. Check-list of North American Birds, 6th edition. Allen Press, Inc., Lawrence, Kansas. 877 pp.

  • 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/.

  • Bailey, F. M. 1935. Handbook of birds of the western United States. Houghton Mifflin Company, Boston and New York.

  • Bailey, F.M. 1928. Birds of New Mexico. New Mexico Department of Game and Fish.

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

  • Barlow, J. C. 1977. Effects of habitat attrition on vireo distribution and population density in the northern Chihuahuan Desert. Pages 591-596 in R. H. Wauer and D. H. Riskind, editors. Trans. Symposium on the Biological Resources of the Chihuahuan Desert, United States and Mexico, Proceedings of a USDI National Park Service Transaction Series No. 3. 658 pp.

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