Icterus graduacauda - Lesson, 1839
Audubon's Oriole
Taxonomic Status: Accepted
Related ITIS Name(s): Icterus graduacauda Lesson, 1839 (TSN 179065)
French Common Names: Oriole d'Audubon
Spanish Common Names: Bolsero Cabeza Negra
Unique Identifier: ELEMENT_GLOBAL.2.100928
Element Code: ABPBXB9180
Informal Taxonomy: Animals, Vertebrates - Birds - Perching Birds
 
Kingdom Phylum Class Order Family Genus
Animalia Craniata Aves Passeriformes Icteridae Icterus
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: Icterus graduacauda
Taxonomic Comments: Possibly closely related to I. chrysater (AOU 1998).
Conservation Status
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NatureServe Status

Global Status: G5
Global Status Last Reviewed: 02Feb2000
Global Status Last Changed: 04Dec1996
Rounded Global Status: G5 - Secure
Nation: United States
National Status: N3 (19Mar1997)

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 Texas (S4B)

Other Statuses

IUCN Red List Category: LC - Least concern

NatureServe Global Conservation Status Factors

Range Extent Comments: RESIDENT: Pacific slope from Nayarit to southern Oaxaca and Caribbean slope from southern Texas (uncommon) and Nuevo Leon to central Veracruz (AOU 1998).

Number of Occurrences: 81 to >300
Number of Occurrences Comments: Appears to presently occur within majority of range historically described from south-central Texas through Mexico. Historic occurrences as a breeding bird in the lower Rio Grande Valley were probably extirpated in the mid-1980's. The remaining Texas occurrences are estimated to be poor to good, and may not all be viable in isolated and degraded habitats. Breeding populations in Texas are regularly searched for through the BBS and the CBC, though lack of access to many private lands makes thorough surveys difficult. May be < 20 occurrences in Texas. The majority of occurrences are in Mexico in central and southern portions of range; these are estimated to be fair to excellent. However, the degree of confidence in estimated total occurrences and occurrence quality are low due to inadequate data.

Population Size: 10,000 to >1,000,000 individuals
Population Size Comments: Local and uncommon in south-central Texas. Elsewhere abundance is described as "common" to "rare" in various wooded habitat types in Oaxaca, Tamaulipas, and adjoining Mexican states (Binford 1989, Peterson and Chalif 1973). No census data is available.

Overall Threat Impact Comments: The combined effects of woodland habitat loss and parasitism by cowbirds have been assumed to be responsible for decreasing populations in southern Texas to dangerously low levels (Flood 1990, Lowther 1995, Oberholser 1974). Some populations in Mexico may be secure (Binford 1989). HABITAT: Where still breeding in Texas, populations are vulnerable to extirpation from widespread degradation of woodlands and subtropical evergreen forests, particularly through dewatering and conversion of wooded ranchlands to farmlands (Brush, pers. comm.). PARASITISM: A commonly recorded host of the bronzed cowbird (MOLOTHRUS AENEUS; Lowther 1995, Bent 1958). Though samples sizes are small, perhaps 50 percent of nests are parasitized (Bent 1958). Bronzed cowbirds seem to have had a particularly deleterious effect in the northernmost portions of the taxon's range, specifically in southern Texas, which has only recently been invaded by substantial numbers of this cowbird species (Oberholser 1974, Flood 1990). Clearing of woodlands permitted northward expansion of cowbird into the United States. Similarly, settlement and agricultural activities in Mexico have increased suitable habitat and have likely led to increased numbers of cowbirds, though regional impacts to this oriole are undocumented (Lowther 1995). Both sexes chase intruding cowbirds, but are often overwhelmed. During four hours of observation Flood (1990) observed cowbirds, often 5 to 10 at a time, approach or enter one oriole nest 10 times.

Short-term Trend Comments: Ceased breeding in the Lower Rio Grande Valley (LRGV) in the mid-1980's, though continues to breed regularly in thorn forest and oak woodland habitats further north (Brush, pers. comm.). In Mexico, described as "common" to "rare" in various wooded habitat types in the states of Oaxaca, Tamaulipas, and Chiapas (Binford 1989, Peterson and Chalif 1973). No trend information is available for Mexico.

Other NatureServe Conservation Status Information

Distribution
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Global Range: RESIDENT: Pacific slope from Nayarit to southern Oaxaca and Caribbean slope from southern Texas (uncommon) and Nuevo Leon to central Veracruz (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 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

Ecology & Life History
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Basic Description: A bird (oriole).
General Description: SONG: low whistled notes of human quality, disjointed, with halftones (Peterson and Chalif 1973).
Diagnostic Characteristics: The only black-headed oriole with a yellowish back.
Reproduction Comments: Eggs are laid in April-June. Clutch size is three to five. Pale bluish white; sometimes blotched, streaked profusely with brown, purples. Only the female incubates. Renesting may occur (Bent 1958, Harrison 1978, Terres 1980, Flood 1990). Nest woven of strands of palmetto leaves, fine wire-like grasses, lined with fine grass tops or unlined; a semipensile cup-like basket, typically about 7.6 centimeters deep, 1.8-33 meters above ground (Bent 1958, Flood 1990, Harrison 1978).
Ecology Comments: Breeds in relatively low densities of 0.1 pair per hectare (Harrell 1951). Frequently found in pairs throughout the year (Bent 1958, Oberholser 1974, Harrell 1951). Often feed in small, mixed-species flocks during the dry winter months (Harrell 1951, Sutton and Pettingill 1942). May forage close to ground (Terres 1980).
Non-Migrant: Y
Locally Migrant: N
Long Distance Migrant: N
Mobility and Migration Comments: Largely sedentary and resident. Many apparently stay on or near the breeding grounds year round (Binford 1989, Flood 1990). May wander north in late winter or early spring (Bent 1958, Oberholser 1974).
Palustrine Habitat(s): Riparian
Terrestrial Habitat(s): Forest - Hardwood, Shrubland/chaparral, Woodland - Hardwood, Woodland - Mixed
Habitat Comments: Gallery forest, pine-oak forest, tropical lowland evergreen forest, tropical deciduous forest, cloud forest, thorn forest. 0-2500 meters; upper Tropical and Subtropical zones (AOU 1998, Flood 1990). Scrub, mesquite, riparian thickets, pine-oak association, humid montane forest edge (AOU 1983). In semi-arid northern range found in dense forests along stagnant water courses, the former beds of streams, or in other wooded regions; these usually contain large specimens of mesquite (PROSOPIS spp.), hackberry (CELTIS LAEVIGATA), ebony (PITHECELLOBIUM EBANO), huisache (ACACIA FARNESIANA), willow (SALIX spp.), palmettos (SABAL spp.), and live oak (QUERCUS VIRGINIANA), with a heavy undergrowth of shrubs and vines (Bent 1958, Oberholser 1974). In Texas, Oberholser (1974) generally observed preference for use of the tallest and densest trees in the landscape.

In northeastern Tamaulipas, found in cloud forest habitat (an oak-sweet gum-beech association) at 1160 meter elevation. Also at lower-elevation characterized by cultivated fields, scattered palmettos (SABAL spp.), dense 1-2 meter high vines and thorny shrubs (ACACIA spp., LEUCAENA spp.), and woods dominated by cypress (CUPRESSUS spp.) and bamboo (BAMBUSEAE spp.; Flood 1990, Sutton and Pettingill 1942).

Ranges south to Oaxaca and Chiapas. Common from 1,800 to 2,000 meters (locally to 2,438 meters) in humid pine-oak forest and adjacent cloud forest in Pacific Region west of Isthmus, rare at unknown elevation in pine-oak forest of the interior, and very uncommon from 200-215 meters in arid pine-oak forest in the Pacific and the Atlantic Region. Winter commonly down to 275 meters into tropical semideciduous forest of Pacific Region (Binford 1989, Peterson and Chalif 1973).

Nests in dense trees, bushes, or thickets. In Texas often in mesquite and along watercourses, but in Mexico in a variety of locations and trees, both mature and saplings (Bent 1958, Flood 1990). Also observed to place nest in Spanish moss (TILLANDSIA USNEOIDES).

Adult Food Habits: Frugivore, Invertivore
Immature Food Habits: Frugivore, Invertivore
Food Comments: Eats insects and fruit, including beetles, moths, hackberries, and mesquite beans (Bent 1958, Oberholser 1974). Takes insects on cactus (OPUNTIA LINDHEIMERI) and mimosa (Bent 1958, Terres 1980). Nestlings fed various invertebrates, including spiders, and a variety of insects, particularly larval forms (Flood 1990).
Adult Phenology: Diurnal
Immature Phenology: Diurnal
Length: 24 centimeters
Weight: 42 grams
Economic Attributes Not yet assessed
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Management Summary
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Stewardship Overview: Among the least-known of orioles. Already extirpated as a breeding bird in Lower Rio Grande Valley (LRGV) of Texas where once common. Still breeds elsewhere in Texas primarily on extensive wooded ranchlands, but continued presence must be considered tenuous given small number of protected habitats and conversion of woodlands to farmlands. Related factors such as cowbird parasitism are contributing to its present scarcity. Restoration of the LRGV population will be most promising where water and land management maintains or restores mature closed-canopy riparian woodlands and subtropical evergreen forests. In Mexico probably secure in a variety of forest habitats. Close monitoring of breeding populations in Texas and baseline monitoring in Mexico is warranted.
Restoration Potential: Maintaining and expanding suitable habitat is critical towards its conservation as a breeding bird in the U.S. Large oak and thornforest woodlands found in areas such as the Kenedy Ranch are critical population centers. Would likely respond positively to restoration of mature riparian woodland and subtropical evergreen forest habitats in arid portions of its range. Water management, in which water is pumped into floodplain forests, has shown promising early effects on germination of tree seedlings, and may be needed to restore suitable riparian habitat (Brush 1998, Castillo 1997). Control of cowbird populations may enhance nesting success in areas where high rates of nest parasitism are documented.
Preserve Selection & Design Considerations: Optimum patch size and many other aspects of landscape ecology are largely unknown. An "edge" species, although it frequents densely vegetated areas more often than other members of the genus (Bent 1958, Flood 1990). Found most commonly near forest edges, or in trees bordering rivers or fields. Often enters natural or man-made clearings to feed (Flood 1990). Preserves comprised of mature gallery forest, oak woodlands, or thorn forest may be suitable, particularly if breeding populations are already present.
Management Requirements: Conservation of various woodland types is critical. Taxon utilizes a variety of landscapes and habitats including forest openings and edges of cultivated areas. The acceptable frequency and magnitude of forest disturbance, however, is not well documented. Rangeland practices which conserve woodlands and dense understory are preferable to conversion to farmland. During drought, riparian woodland can be maintained by supplemental irrigation (Brush 1999).

Brood parasitism by bronzed cowbirds (MOLOTHRUS AENEUS) has been assumed to reduce reproductive success and may be a factor responsible for declining populations in southern Texas (Flood 1990, Oberholser 1974). Reduction of cowbird subsidies or cowbird population control may improve host reproductive success. Cowbird management, however, is not currently occurring or proposed.

Monitoring Requirements: Detected by both sight and sound. Both sexes sing year round, especially near nest, but primarily near dawn and dusk making detection difficult. Tape playback is one method that has been used to locate the species (Brush, pers. comm.). Nest very difficult to locate (more so than those of other orioles); often concealed among abundant twigs at the central portion of limbs (Flood 1990). Male does not incubate, but often less than 50 meters from nest (15-40 percent time; Flood 1990). Close monitoring of the population is warranted throughout its range in Texas and northern Mexico; baseline distribution and population monitoring elsewhere in Mexico needed.
Management Research Needs: Considerable research is necessary; it is among the least-known of the 25 species of New World orioles (Flood 1990). Much of the life history is poorly documented, especially for Middle America. Information needed on habitat relationships during breeding and winter, reproductive success, home range, habitat fragmentation, sensitivity to different livestock grazing regimes and other land management activities (Brush, pers. comm.).

Parasitism by bronzed cowbirds (MOLOTHRUS AENEUS) deserves special attention. Determining what criteria, if any, are used by cowbirds in selection of nests to parasitize could potentially be helpful to guiding management decisions for rare hosts like this one (Lowther 1995). Reducing key anthropogenic subsidies, such as agricultural wastes, may reduce cowbird parasitism rates or local impacts to host species.

Biological Research Needs: Subspecies need revision, especially in regard to the validity of the races DICKEYAE, NAYARITENSIS, and RICHARDSONI (Binford 1989).
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: 02Feb2000
NatureServe Conservation Status Factors Author: Deeble, B.; revisions by M. Koenen and D.W. Mehlman
Management Information Edition Date: 31Jan2000
Management Information Edition Author: DEEBLE, B.; REVISIONS BY M. KOENEN AND D.W. MEHLMAN
Management Information Acknowledgments: The author thanks David Sarkozi of Birds of the Upper Texas Coast (http://texasbirding.simplenet.com/index.html) for suggesting additional data resources, and Tim Brush for providing recent manuscripts and additional observation on the species. Funding for the preparation of this abstract was made possible by the U.S. Fish and Wildlife Service, Division of Endangered Species.
Element Ecology & Life History Edition Date: 02Feb2000
Element Ecology & Life History Author(s): DEEBLE, B.; REVISIONS BY M. KOENEN AND D.W. MEHLMAN

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

  • Bent, A.C. 1958. Life histories of North American blackbirds, orioles, tanagers, and their allies. U.S. National Museum Bulletin 211. Washington, DC.

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

  • Brush, T. 1998. Recent nesting and current status of Red-billed Pigeon along the lower Rio Grande in southern Texas. Bulletin of the Texas Ornithological Society 31(1):22-26.

  • Brush, T. 1999. Current status of Northern Beardless-Tyrannulet and Tropical Parula in Bentsen-Rio Grande Valley State Park and Santa Ana National Wildlife Refuge, southern Texas. Bulletin of the Texas Ornithological Society 32(1):3-12.

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  • Castillo, C.D. 1997. Effects of artificial flooding on the vegetation and avifauna of riparian woodlands at Santa Ana National Wildlife Refuge, Hidalgo Co., Texas. Unpublished master's thesis, Univ. of Texas-Pan American, Edinburg, 55 pp.

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  • Ehrlich, P. R., D. S. Dobkin, and D. Wheye. 1992. Birds in Jeopardy: the Imperiled and Extinct Birds of the United States and Canada, Including Hawaii and Puerto Rico. Stanford University Press, Stanford, California. 259 pp.

  • Flood, N. J. 1990. Aspects of the breeding biology of Audubons oriole. Journal of Field Ornithology 61(3):290-302.

  • Harrell, B.C. 1951. The birds of Rancho del Cielo, an ecological investigation in the oak-sweet gum forests of Tamaulipas, Mexico. M.A. thesis, University of Minnesota, Minneapolis, Minnesota.

  • Harrison, C. 1978. A Field Guide to the Nests, Eggs and Nestlings of North American Birds. Collins, Cleveland, Ohio.

  • Harrison, H. H. 1979. A field guide to western birds' nests. Houghton Mifflin Company, Boston. 279 pp.

  • Horn, H. S. 1968. The adaptive significance of colonial nesting in the Brewer's Blackbird. Ecology 49:682-694.

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Ridgely, R.S., T.F. Allnutt, T. Brooks, D.K. McNicol, D.W. Mehlman, B.E. Young, and J.R. Zook. 2003. Digital Distribution Maps of the Birds of the Western Hemisphere, version 1.0. NatureServe, Arlington, Virginia, USA.

Acknowledgement Statement for Bird Range Maps of North America:
"Data provided by NatureServe in collaboration with Robert Ridgely, James Zook, The Nature Conservancy - Migratory Bird Program, Conservation International - CABS, World Wildlife Fund - US, and Environment Canada - WILDSPACE."

Citation for Mammal Range Maps of North America:
Patterson, B.D., G. Ceballos, W. Sechrest, M.F. Tognelli, T. Brooks, L. Luna, P. Ortega, I. Salazar, and B.E. Young. 2003. Digital Distribution Maps of the Mammals of the Western Hemisphere, version 1.0. NatureServe, Arlington, Virginia, USA.

Acknowledgement Statement for Mammal Range Maps of North America:
"Data provided by NatureServe in collaboration with Bruce Patterson, Wes Sechrest, Marcelo Tognelli, Gerardo Ceballos, The Nature Conservancy-Migratory Bird Program, Conservation International-CABS, World Wildlife Fund-US, and Environment Canada-WILDSPACE."

Citation for Amphibian Range Maps of the Western Hemisphere:
IUCN, Conservation International, and NatureServe. 2004. Global Amphibian Assessment. IUCN, Conservation International, and NatureServe, Washington, DC and Arlington, Virginia, USA.

Acknowledgement Statement for Amphibian Range Maps of the Western Hemisphere:
"Data developed as part of the Global Amphibian Assessment and provided by IUCN-World Conservation Union, Conservation International and NatureServe."

NOTE: Full metadata for the Bird Range Maps of North America is available at:
http://www.natureserve.org/library/birdDistributionmapsmetadatav1.pdf.

Full metadata for the Mammal Range Maps of North America is available at:
http://www.natureserve.org/library/mammalsDistributionmetadatav1.pdf.

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