Toxostoma curvirostre - (Swainson, 1827)
Curve-billed Thrasher
Other English Common Names: curve-billed thrasher
Taxonomic Status: Accepted
Related ITIS Name(s): Toxostoma curvirostre (Swainson, 1827) (TSN 178637)
French Common Names: Moqueur ā bec courbe
Spanish Common Names: Cuitlacoche Pico Curvo
Unique Identifier: ELEMENT_GLOBAL.2.100883
Element Code: ABPBK06070
Informal Taxonomy: Animals, Vertebrates - Birds - Perching Birds
Image 11245

© Larry Master

 
Kingdom Phylum Class Order Family Genus
Animalia Craniata Aves Passeriformes Mimidae Toxostoma
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: Toxostoma curvirostre
Taxonomic Comments: May be comprised of more than one species (Tweit 1996). Mitochondrial DNA analysis by Zink et al. (2001) show a genetic division between populations of the Sonoran and Chihuahuan deserts. Monroe and Sibley (1990) suggest that this taxon appears to constitute a superspecies with T. OCELLATUM, but this hypothesis is not supported by phylogenetic analysis of Zink et al. (1999), who state that "The relationships of T. CURVIVROSTRE and T. OCELLATUM are problematic, and the two taxa do not appear to be sister species." Placed in Sturnidae in Sibley and Ahlquist (1984).
Conservation Status
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NatureServe Status

Global Status: G5
Global Status Last Reviewed: 03Dec1996
Global Status Last Changed: 03Dec1996
Rounded Global Status: G5 - Secure
Nation: United States
National Status: N5 (05Jan1997)

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 (S5), Colorado (S3), Kansas (S1B), New Mexico (S5B,S5N), Oklahoma (S3), Texas (S4B)

Other Statuses

IUCN Red List Category: LC - Least concern

NatureServe Global Conservation Status Factors

Range Extent Comments: RESIDENT: northwestern Arizona, northeastern New Mexico, southeastern Colorado, western Oklahoma, southwestern Kansas, and central Texas south to northwestern Nayarit, through Mexican Plateau to central Oaxaca and Veracruz, and central Tamaulipas (Tweit 1996, AOU 1998).

Overall Threat Impact Comments: PREDATION: Suspected predators of eggs, nestlings, and fledglings include striped whipsnakes (MASTICOPHIS TAENIATUS), Texas patchnosed snakes (SALVADORA GRAHAMIAE), western diamondback rattlesnakes (CROTALUS ATROX), and ants (Formicidae). Confirmed nest predators include coachwhips (MASTICOPHIS FLAGELLUM), bullsnakes (PITUOPHIS MELANOLEUCUS), kingsnakes (LAMPROPELTIS GETULA), desert spiny lizards (SCELOPORUS MAGISTER), roadrunners (GEOCCOCYX CALIFORNIANUS), round-tailed ground squirrels (CITELLUS TERETICAUDUS), Harris' antelope ground squirrels (AMMOSPERMOPHILUS HARRIS), and Harris' hawk (PARABUTEO UNICINCTUS; Fischer 1980, Tweit 1996). PARASITISM: Brood parasitism by cowbirds (MOLOTHRUS spp.) is rare (Tweit 1996). HABITAT: Its preferred U.S. habitats, the Texas brushlands and the Sonoran Desert in Arizona, are being lost to development and conversion to grassland monocultures (especially buffel grass, PENNISETUM CITUARE; Tweit 1996).

Short-term Trend Comments: North American Breeding Bird Survey (BBS) data indicate a statistically significant decline (-3.6 percent per year) for the U.S., 1966 through 1996. The most significant declines have occurred in Texas (-4.35 percent per year; Sauer et al. 1997). Declines in Texas have also been corroborated by the Christmas Bird Count (CBC; -2.5 percent per year from 1959-1988; Sauer et al. 1996).

Other NatureServe Conservation Status Information

Distribution
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Global Range: RESIDENT: northwestern Arizona, northeastern New Mexico, southeastern Colorado, western Oklahoma, southwestern Kansas, and central Texas south to northwestern Nayarit, through Mexican Plateau to central Oaxaca and Veracruz, and central Tamaulipas (Tweit 1996, AOU 1998).

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, CO, KS, NM, OK, TX

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)
KS Gray (20069), Morton (20129)
NM Socorro (35053)*
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
11 Arkansas-Dodge City (11030003)+, Upper Cimarron (11040002)+, Upper Cimarron-Liberal (11040006)+, Crooked (11040007)+
13 Jornada Del Muerto (13020210)+*, Tularosa Valley (13050003)+*
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
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Basic Description: A bird (thrasher).
Diagnostic Characteristics: See Kaufman and Bowers (1990) for detailed information on identification.
Reproduction Comments: Phenology of breeding season is influenced by temperature and timing and amount of rainfall. Although most eggs are laid between March and May in Arizona, egg laying can begin as early as late January (Tweit 1996). The nesting season recorded during a two-year period in southern Texas ranged from 13 April through 20 July (Fischer 1980). Nesting in the Rio Grande Valley of Texas begins in March (Bent 1948). Normally two clutches are produced in south Texas, but up to three can be produced if the first two clutches fail (Fischer 1980). In Arizona, an average of 2.2 (maximum of four) clutches are laid (Anderson and Anderson 1973). Average clutch size is 3.8 eggs (range = 3-5) in south Texas; 2.8 eggs (range = 2-4) in Sonora, Mexico; and 3.2, 2.5, and 2.7 eggs for three studies in Arizona (Fischer 1980, Tweit 1996). Larger average clutch size in Texas may correlate with a more reliable food supply (R. Tweit, pers. comm.).

Incubation is initiated before all eggs are laid. Both sexes incubate the eggs an average of 14 days (range = 12-15), but females incubate for longer periods than males (Fischer 1980, Hensley 1959). Hatching success varies from 54.5 percent-71 percent across the range (Tweit 1996). Nesting success is 44 percent in south Texas, with predation accounting for 40 percent of the loss of eggs/young. Nests constructed in yucca are significantly more successful than those placed in other vegetation, and shaded nests are more successful than unshaded nests (Fischer 1980, Tweit 1996).

In Arizona, nesting success ranges from 21-44.5 percent (Anderson and Anderson 1973, Edwards and Stacy 1968 cited in Tweit 1996). Parent birds preferentially feed larger, older nestlings during food shortages resulting in brood reduction by starvation of younger nestlings (Ricklefs 1965). Both sexes feed the young (Fischer 1980, Hensley 1959). Sexually matures in one year (Tweit 1996).

Ecology Comments: Population density varies with habitat disturbance. In Arizona, an average of 63 thrashers per square kilometer inhabit undisturbed to moderately disturbed palo verde-saguaro habitat; only 6.5 individuals per square kilometer inhabit disturbed palo verde-saguaro habitat dominated by exotic vegetation (Tweit and Tweit 1986). In south Texas brushland, Emlen (1972) estimated a density of 5-10 thrashers per square kilometer. Abundances for three BBS routes range from an average of 9.3-39 individuals per route (Price et al 1995).

Each pair maintains a permanent, year-round territory. Territory size ranges from 2 hectares in south Texas brushland to 2.5-4.5 hectares in palo verde-saguaro habitat in Arizona (Fischer 1980, Tweit 1996). In south Texas, six pairs renested within 30 meters of where they nested the previous year; two pairs nested within 60 and 75 meters of previous nests; and one remated female nested within 100 meters of her previous nest (Fischer 1980). In Arizona, two males nested in their respective territories annually for six years (Anderson and Anderson 1973).

Oldest, known-age wild bird lived 10 years, 9 months. The recapture of only 6 percent of 345 young banded from one month-one year earlier in Arizona suggests high juvenile mortality and/or dispersal (Tweit 1996). In south Texas, 94 percent of adults survived from one breeding season to the next (Fischer 1980). Average annual survival of adults in Arizona was 79 percent (Anderson and Anderson 1973). The sex ratio approximates unity, but quantitative data are unavailable (Tweit 1996).

Non-Migrant: Y
Locally Migrant: N
Long Distance Migrant: N
Mobility and Migration Comments: Considered partly migratory; however, juvenile dispersal may be mistaken for migration (Tweit 1996).
Terrestrial Habitat(s): Desert, Shrubland/chaparral
Habitat Comments: Inhabits arid thornscrub, chaparral, cholla (OPUNTIA) grasslands, and other brushy areas (Terres 1991, Tweit 1996). Typical woody vegetation of occupied Texas chaparral includes mesquite (PROSOPIS GLANDULOSA), colima (ZANTHOXYLUM FAGARA), acacia (ACACIA RIGIDULA), agarito (BERBERIS TRIFOLIATA), brasil (CONDALIA HOOKERI), and granjeno (CELTIS PALLIDA; Fischer 1980, 1981). Inhabits creosote bush (LARREA TRIDENTATA) communities, the palo verde-saguaro community, cholla grasslands, and thornscrub in Arizona; cholla grasslands in Colorado and adjacent states; and thornscrub and brushy field edges in Mexico. Also inhabits meadows and fields adjacent to pine (PINUS)-oak (QUERCUS) woodlands in Arizona and New Mexico (Marshall 1957, Phillips et al. 1964, Terres 1991, Tweit 1996). Inhabits cities in Arizona (Bent 1948, Phillips et al. 1964).

Nests in a wide variety of cacti, shrubs and small trees throughout its range. In south Texas, nests are located most often in yucca (YUCCA TRECULEANA), oak (QUERCUS VIRGINIA), and colima (Fischer 1980). Nests in tree cholla (OPUNTIA IMBRICATA) and mesquite in Oklahoma; jumping cholla (O. FULGIDA), soaptree yucca (Y. ELATA), jujube (ZIZIPHUS JUJUBA), mistletoe (PHORADENDRON), LYCIUM, mesquite, and occasionally, in woodpecker holes in saguaro and sycamore (PLANTANUS WRIGHTII) in Arizona; and in cholla cactus, nopalo cactus (O. FICUS-INDICA), acacia (A. GREGGII), prickly pear (OPUNTIA spp.), organ pipe cactus (CEREUS THURBERI), mesquite, and oak in Mexico (Clark 1904; Gilman 1909; Hensley 1959; Tweit 1996; R. Tweit, pers. comm.). Nest height ranges from 0.7-6.0 meters above the ground, but the majority are built 1-2 meters high (Anderson and Anderson 1973, Clark 1904, Gilman 1909, Hensley 1959, Tweit 1996).

Adult Food Habits: Frugivore, Granivore, Invertivore
Immature Food Habits: Frugivore, Granivore, Invertivore
Food Comments: Forages primarily on the ground, using beak to probe soil and leaf litter and sweep leaf litter aside. Also digs into soil and moves cover objects (woody debris, cow and horse manure) to expose invertebrate prey beneath (Bent 1948, Marshall 1957, Fischer 1981). Will ascend shrubs and trees to forage on berries (Fischer 1981). Where sympatric, curve-billed thrashers forage in more open areas than long-billed (TOXOSTOMA LONGIROSTRE) or brown thrashers (T. RUFUM; Fischer 1981). Omnivorous and opportunistic feeder; diet includes a wide variety of animal and plant matter. Stomach contents vary among location and temporally in the same location (R. Tweit, pers. comm.). Nine stomachs examined by Marshall (1957) contained (in order of decreasing frequency) plant bulbs, rocks, seeds, insects, green plant material and a large grub. Fischer (1981) found 73 percent arthropod matter and 28 percent plant matter in seven stomachs collected in October, and 94 percent arthropod matter and 6 percent plant matter in three stomachs collected in March. Beetles (Coleoptera) dominated the arthropod portion of the diet, whereas fruits of hackberry (CELTIS LAEVIGATA) and brasil comprised most of the plant material. Eight stomachs collected in spring and 10 collected in summer contained 44 percent:56 percent and 29 percent:71 percent Plant:animal matter, respectively (Martin et al. 1951). Plant foods include prickly pear, wheat (TRITICUM), corn (ZEA MAYS), brasil, chufa (CYPERUS), barley (HORDEUM VULGARE), nightshade (SOLANUM), hackberry, and bristlegrass (SETARIA). In south Texas, terrestrial arthropods comprised 97 percent of the diet of nestlings; principal prey groups included orthopterans (60.4 percent), coleopterans (16.4 percent), lepidopterans (12.4 percent), and arachnids (7 percent; Fischer 1983). Probes the deep flowers of saguaros, apparently for nectar (Anderson and Anderson 1973). Will feed at feeders. Water is obtained from fleshy fruit of cacti, water holes, dripping faucets and bird baths (Bent 1948).
Adult Phenology: Diurnal
Immature Phenology: Diurnal
Length: 28 centimeters
Weight: 79 grams
Economic Attributes Not yet assessed
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Management Summary
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Stewardship Overview: Although capable of inhabiting urban and suburban environments when native vegetation is maintained, populations have declined 61.8 percent from 1966-1993 as detected by North American Breeding Bird Survey (BBS; Price et al. 1995). The decline is attributable to loss of habitat, principally as a result of development. Conversion of shrubland to grassland has also contributed to habitat loss. BBS and Christmas Bird Counts provide valuable data on population trends.
Restoration Potential: Could probably be restored to areas of former occurrence following restoration of native vegetation.
Management Requirements: When native vegetation is maintained, residential development in the palo verde (CERCIDIUM MICROPHYLLUM)-saguaro (CARNEGIA GIGANTEA) community of Arizona at a density of two houses per hectare does not reduce thrasher density (Tweit and Tweit 1986).
Management Research Needs: Need to generate and enforce standards for compatible development to avoid further reductions in population densities.
Biological Research Needs: Taxonomic studies needed to understand subspecies relationships; preliminary mitochondrial DNA evidence suggests the thrasher may actually be more than one species. Studies of juvenile dispersal are needed to resolve questions about migration. Identification of and ecological relationship to parasites needed (Tweit 1996).
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: 30Nov1999
Management Information Edition Author: PALIS, J.; REVISIONS BY M. KOENEN AND D.W. MEHLMAN
Management Information Acknowledgments: The author thanks Dr. Robert Tweit for his thoughtful review of a draft of this abstract. Funding for the preparation of this abstract was provided through the Great Plains Bird Conservation Planning Team, supported by The Nature Conservancy's Wings of the Americas, Ecoregional Conservation, and Great Plains Programs.
Element Ecology & Life History Edition Date: 30Nov1999
Element Ecology & Life History Author(s): PALIS, J., AND G. HAMMERSON

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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