The sage thrasher (Oreoscoptes montanus) is a medium-sized passerine bird in the family Mimidae. It is the only species in the genus Oreoscoptes and the smallest of the thrashers. It is found in the regions of western North America, breeding from the Great Basin to southern British Columbia, and migrates south to southern United States and northern Mexico for winter. Sage thrashers are commonly found in shrubsteppe habitat and are strongly associated with sagebrush (Artemisia spp.) for which it relies on for nesting.

Description

The sage thrasher is a medium-sized passerine, measuring 20.0-23.0 cm in length and weighing 39.6-50.3g. Its eyes are distinctive ranging from lemon-yellow to amber coloration. Juveniles have paler upperparts and lightly streaked underparts compare to the adults. Adults display brownish-gray upperparts and white underparts marked with dark streaks. Plumage remains relatively similar throughout the year. Sage thrasher can be distinguished from other thrashers by its shorter and less curved bill, shorter tail and smaller size.alt=Sage Thrasher|left|thumb|309x309px|Sage Thrasher wintering in [[Woodland, California. February 2017.]]

Taxonomy

The species was first described by the ornithologist John Kirk Townsend in 1837 and was given the name of "mountain mockingbird", but was later changed to its current name "sage thrasher" for looking more similar to thrasher than mockingbirds and based on their habitat. Just like the sage thrasher, "sage" has been used to name other birds species that are strongly associated with sagebrush such as Greater sage-grouse and the Sagebrush sparrow. The genus name Oreoscoptes comes from the Greek oreos, "mountain", and skōptō, "mocker". Montanus in Latin means "from the mountains".

The species is more closely related to the genus Mimus, which includes the typical mockingbirds, than to Toxostoma, the genus that includes the typical thrashers. As a results, thrashers are consider a phenetic assemblage, a group classified based on morphological similarities rather than by shared ancestry, as members of the group are paraphyletic. The genus Oreoscoptes is monotypic, containing only the sage thrasher.

Habitat and Distribution

The sage thrasher breeds in shrubsteppe habitats dominated by big sagebrush (Artemisia tridentata) across the western United States and southern Canada. Sagebrush are essential for nesting and provides protection from the heat and from predators. The abundance of sage thrasher is positively correlated with the amount of sagebrush cover in an area as well as with woody vegetation and bare ground, and negatively with grass cover.

The northern limit of the sage thrasher for breeding extends into south-central British Columbia, Canada, in Similkameen and Okanagan valleys. In the United States, the species breeds from central Washington southward through eastern Oregon and the northerneastern part of California. Its range extaends eastward across Nevada, Utah, western Colorado, southern Idaho, Wyoming, southern Montana, and into northern Arizona and New Mexico. During winter, the sage thrasher occurs from souther from southern Nevada through central and southern Arizona, central and southern New Mexico, and west-central Texas. In Mexico, its wintering range includes northern Baja California, northwestern and central Sonora, northern Chihauahua, and Nuevo León, extending south to south to Durango. Sage thrasher are short-distance migrant and migrate towards their breeding range in early spring and leave for their wintering range in early fall.

Behaviour and ecology

Vocalization

Sage thrashers sing to attract mates and establish territories. During migration to their breeding grounds, silent individuals travel ahead of occupied territories by others until they reach an unoccupied one, where they begin to sing they are established. Singing is most frequent during territory establishment and pair formation, and stop when nest building starts. Singing typically occurs when perch on top of surrounding vegetation. Like some of its relatives, the sage thrasher is capable of vocal mimicry and may include imitations of other bird species in its song such as the Western Meadowlark, Brewer's Sparrow and Horned Lark. Nests are either build in the sagebrush or under it where the nest is covered by the shrub. Their breeding habitat is characterized by an extreme temperature fluctuation between day and night, and several studies suggest that sage thrashers construct their nests to buffer against temperature variations. They often place their nest in the densest parts of the vegetation, sometimes beneath old nest for additional shading, and at optimal height to take advantage of cooler air near the ground and wind that helps dissipate heat. This placement may also aid to conceal nest from aerial predators.

The nest is cup-shaped, about 10 cm in height and 18–20 cm in diameter and is built with parts of sagebrush such as twigs, bark strips, rootlets and can also contains cowhairs and feathers. Characteristics that supports the species ability to reject cowbird eggs include visual distinctiveness between sage thrasher and cowbird eggs, the species practice of nest sanitation, large and accessible nests that attracts parasitism, and has a large enough bill to eject eggs.

Diet

thumb|Sage thrasher at Seedskadee National Wildlife Refuge eating a berry

Sage thrashers primarily forage on the ground feeding, feeding mainly on terrestrial insects. They are opportunistic feeders, and their diet reflects the prey availability in their environment. Food items include ants, ground beetles, true bugs, grasshoppers, and crickets. Shrubsteppe habitats converted into urban development or agricultural land have historically caused local extirpation of the species in some of its range. Annual grass cover such as cheatgrass (Bromus tectorum) in shrubsteppe seems to also be negatively associated with occurrence of sage thrasher for nesting. The presence of loggerhead shrikes appears to reduce the density of nesting passerines, including the sage thrasher, in sagebrush habitat over time.

Conservation

The species in Canada has been classified as an Endangered species by COSEWIC, found in southern British Columbia and Alberta. Reasons for designation are that it is very small population of an estimated 7 to 36 adults, low level of immigration from Washington and Montana, and reduction of sage-brush habitat due to anthropogenic development and fires.

In Washington, the Washington Department of Fish & Wildlife (WDFW) consider the sage thrasher as a Species of Greatest Conservation Need under the State Wildlife Action Plan and identified as a Priority Species under the WDFW's Priority Habitat and Species Program. Conservation concerns include declining population and range reduction occupied by the species.

References

  • Sage Thrasher Species Account - Cornell Lab of Ornithology
  • Sage Thrasher Bird Sound - Xeno-canto
  • Sage Thrasher Oreoscoptes montanus - USGS Patuxent Bird Identification InfoCenter
  • Sage Thrasher photo gallery VIREO
  • Sage Thrasher videos on the Internet Bird Collection
  • Photo and description - Utah Division of Wildlife Resources

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Further reading

Book

  • Reynolds, T. D., T. D. Rich, and D. A. Stephens. 1999. Sage Thrasher (Oreoscoptes montanus). In The Birds of North America, No. 463 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.

Thesis

  • Castrale JS. Ph.D. (1981). USE OF MANAGED SAGEBRUSH GRASSLANDS BY BIRD POPULATIONS. Brigham Young University, United States -- Utah.
  • Howe FP. Ph.D. (1993). Effects of an experimental food reduction on nesting shrubsteppe passerines. Colorado State University, United States -- Colorado.
  • Johnson E. M.S. (2005). Bird and small mammal communities of sagebrush-dominated mountain meadows: An examination of meadow characteristics as part of a hierarchical, multi-level study of the Wasatch-Cache National Forest. Utah State University, United States -- Utah.
  • McIntyre KK. M.S. (2003). Species composition and beta diversity of avian communities along a burned/unburned gradient in sagebrush steppe habitat at Sheldon National Wildlife Refuge, Nevada. Sul Ross State University, United States -- Texas.
  • Petersen KL. Ph.D. (1986). AVIAN ECOLOGICAL STUDIES IN A SAGEBRUSH COMMUNITY: BIRD RESPONSES TO FIRE AND TERRITORY DYNAMICS IN A SPARROW POPULATION (IDAHO). Iowa State University, United States -- Iowa.

Articles

  • Amin OM & Dailey MD. (1998). Description of Mediorhynchus papillosus (Acanthocephala: Gigantorhynchidae) from a Colorado, U.S.A., population, with a discussion of morphology and geographical variability. Journal of the Helminthological Society of Washington. vol 65, no 2. p. 189-200.
  • Belthoff JR, Powers LR & Reynolds TD. (1998). Breeding birds at the Idaho National Engineering and Environmental Laboratory, 1985-1991. Great Basin Naturalist. vol 58, no 2. p. 167-183.
  • Bielefeldt J. (1973). Sage Thrasher in Waukesha County. Passenger Pigeon. vol 35, no 1. p. 35-36.
  • Castrale JS. (1982). Effects of 2 Sagebrush Artemisia-Spp Control Methods on Nongame Birds. Journal of Wildlife Management. vol 46, no 4. p. 945-952.
  • Fischer DH. (1983). Growth Development and Food Habits of Nestling Mimids in South Texas USA. Wilson Bulletin. vol 95, no 1. p. 97-105.
  • Howe FP. (1992). Effects of Protocalliphora-Braueri Diptera Calliphoridae Parasitism and Inclement Weather on Nestling Sage Thrashers. Journal of Wildlife Diseases. vol 28, no 1. p. 141-143.
  • Howe FP, Knight RL, McEwen LC & George TL. (1996). Direct and indirect effects of insecticide applications on growth and survival of nestling passerines. Ecological Applications. vol 6, no 4. p. 1314-1324.
  • Howe FP, Knight RL, McEwen LC & George TL. (2000). Diet switching and food delivery by shrubsteppe passerines in response to an experimental reduction in food. Western North American Naturalist. vol 60, no 2. p. 139-154.
  • Ingelfinger F & Anderson S. (2004). Passerine response to roads associated with natural gas extraction in a sagebrush steppe habitat. Western North American Naturalist. vol 64, no 3. p. 385-395.
  • Johnston DW. (1969). Sage Thrasher and Other Unusual Birds in North-Central Florida. Auk. vol 86, no 4. p. 754-755.
  • Killpack ML. (1970). Notes on Sage Thrasher Nestlings in Colorado. Condor. vol 72, no 4. p. 486-488.
  • Knick ST & Rotenberry JT. (1995). Landscape characteristics of fragmented shrubsteppe habitats and breeding passerine birds. Conservation Biology. vol 9, no 5. p. 1059-1071.
  • Knick ST & Rotenberry JT. (2000). Ghosts of habitats past: Contribution of landscape change to current habitats used by shrubland birds. Ecology. vol 81, no 1. p. 220-227.
  • Knick ST & Rotenberry JT. (2002). Effects of habitat fragmentation on passerine birds breeding in Intermountain shrubsteppe. Studies in Avian Biology. vol 25, p. 130-140.
  • Lavers N. (1980). Sage Thrasher Oreoscoptes-Montanus New-Record Arkansas USA. Arkansas Academy of Science Proceedings. vol 34, no 122.
  • McNicholl MK. (1973). Sight Record of Sage Thrasher near Cache Creek British-Columbia. Canadian Field Naturalist. vol 87, no 4.
  • Medin DE. (1992). BIRDS OF A GREAT-BASIN SAGEBRUSH HABITAT IN EAST-CENTRAL NEVADA. Usda Forest Service Intermountain Research Station Research Paper. no 452. p. U1-U4.
  • Noson AC, Schmitz RA & Miller RF. (2006). Influence of fire and Juniper encroachment on birds in high-elevation sagebrush steppe. Western North American Naturalist. vol 66, no 3. p. 343-353.
  • Petersen KL & Best LB. (1991). Nest-Site Selection by Sage Thrashers in Southeastern Idaho. Great Basin Naturalist. vol 51, no 3. p. 261-266.
  • Reynolds TD. (1981). Nesting of the Sage Thrasher Oreoscoptes-Montanus Sage Sparrow Amphispiza-Belli and Brewers Sparrow Spizella-Breweri in Southeastern Idaho USA. Condor. vol 83, no 1. p. 61-64.
  • Reynolds TD & Rich TD. (1978). Reproductive Ecology of the Sage Thrasher Oreoscoptes-Montanus on the Snake River Plain in South Central Idaho USA. Auk. vol 95, no 3. p. 580-582.
  • Rich T. (1980). Nest Placement in Sage Thrashers Oreoscoptes-Montanus Sage Sparrows Amphispiza-Belli and Brewers Sparrows Spizella-Breweri. Wilson Bulletin. vol 92, no 3. p. 362-368.
  • Rich T. (1985). A Sage Thrasher Oreoscoptes-Montanus Nest with Constructed Shading Platform. Murrelet. vol 66, no 1. p. 18-19.
  • Rich T & Rothstein SI. (1985). Sage Thrashers Oreoscoptes-Montanus Reject Cowbird Molothrus-Ater Eggs. Condor. vol 87, no 4. p. 561-562.
  • Rich TDG. (1980). Bilateral Wing Display in the Sage Thrasher Oreoscoptes-Montanus. Wilson Bulletin. vol 94, no 4. p. 512-513.
  • Rose BJ. (1969). Sage Thrasher in Pennington County. South Dakota Bird Notes. vol 21, no 4.
  • Rotenberry JT & Wiens JA. (1989). Reproductive Biology of Shrubsteppe Passerine Birds Geographical and Temporal Variation in Clutch Size Brood Size and Fledging Success. Condor. vol 91, no 1. p. 1-14.
  • Rowlett RA. (1972). 1st Sage Thrasher for Maryland. Atlantic Naturalist. vol 27, no 2. p. 85-86.
  • Vander Haegen WM, Schroeder MA & Degraaf RM. (2002). Predation on real and artificial nests in shrubsteppe landscapes fragmented by agriculture. Condor. vol 104, no 3. p. 496-506.
  • Weber JW & Larrison EJ. (1976). Status of the Sage Thrasher in Asotin County Washington and Adjacent Idaho. Murrelet. vol 57, no 3.
  • Wiens JA & Rotenberry JT. (1980). Patterns of Morphology and Ecology in Grassland and Shrub Steppe Bird Populations. Ecological Monographs. vol 50, no 3. p. 287-308.
  • Wiens JA, Rotenberry JT & Van Horne B. (1987). Habitat Occupancy Patterns of North American Shrubsteppe Birds the Effects of Spatial Scale. Oikos. vol 48, no 2. p. 132-147.
  • Williams NS. (1983). 3 New Species of Brueelia Mallophaga Philopteridae from the Mimidae Aves Passeriformes. Proceedings of the Biological Society of Washington. vol 96, no 4. p. 599-604.
  • Wilson Ornithol Soc Conserv C. (1976). Conservation Committee Report on Effects of Alteration of Sagebrush Communities on the Associated Avi Fauna. Wilson Bulletin. vol 88, no 1. p. 165-171.

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