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Montana Animal Field Guide

Montana Field Guides

Varied Thrush - Ixoreus naevius

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Species of Concern

Global Rank: G5
State Rank: S3B
* (see State Rank Reason below)

Agency Status
USFWS:
USFS:
BLM:
FWP Conservation Tier: 3
PIF: 3


 

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Copyright by: The Macaulay Library at the Cornell Lab of Ornithology, Ithaca, NY, all rights reserved.
State Rank Reason (see State Rank above)
Species has undergone recent population declines in Montana and across the Northern Rockies and faces threats from fire, insect outbreak, and timber harvest related to climate change.
  • Details on Status Ranking and Review
    Varied Thrush (Ixoreus naevius) Conservation Status Review
    Review Date = 12/21/2011
    View State Conservation Rank Criteria
    Population Size

    ScoreG - 100,000-1,000,000 individuals

    CommentRecent Intermountain Bird Conservation Region monitoring data for 2010 estimates the statewide population at 390,594 +/- SD of 85,930.

    Range Extent

    ScoreF - 20,000-200,000 km squared (about 8,000-80,000 square miles)

    Comment139,977 square kilometers based on Natural Heritage Program range maps that appear on the Montana Field Guide.

    Area of Occupancy

    ScoreU - Unknown

    CommentUnknown.

    Long-term Trend

    ScoreE - Relatively Stable (±25% change)

    CommentSpecies favors mesic conifer forests which, in the Northern Rockies, have remained relatively stable within +/- 25% of pre European levels.

    Short-term Trend

    ScoreC - Rapidly Declining. Decline of 30-50% in population, range, area occupied, and/or number or condition of occurrences

    CommentBBS data has moderate credibility in Montana and shows an insignificant decline of -6.7% per year or 51% decline per decade. For the Northern Rockies as a wholethe data has highest credibility and shows a significant decline of -4.3% per year or 46% decline per decade. Idaho, British Columbia, Alberta, Washington, and Oregon all show declines with high credibility.

    Threats

    ScoreB - Moderate and imminent threat. Threat is moderate to severe and imminent for a significant proportion (20-60%) of the population or area.

    CommentFire, timber harvest, and insect outbreak related to climate change are the greatest threats to the species due to its reliance on mature mesic conifer forests.

    SeverityModerate - Major reduction of species population or long-term degradation or reduction of habitat in Montana, requiring 50-100 years for recovery.

    CommentLoss of unbroken stands of mature trees takes a long time to recover.

    ScopeModerate - 20-60% of total population or area affected

    CommentFire and beetle kill are drastically changing a large portion (20-60%) of the landscape.

    ImmediacyModerate - Threat is likely to be operational within 2-5 years.

    CommentOngoing but could accelerate.

    Intrinsic Vulnerability

    ScoreC - Not Intrinsically Vulnerable. Species matures quickly, reproduces frequently, and/or has high fecundity such that populations recover quickly (< 5 years or 2 generations) from decreases in abundance; or species has high dispersal capability such that extirpated populations soon become reestablished through natural recolonization (unaided by humans).

    Comment

    Environmental Specificity

    ScoreB - Narrow. Specialist. Specific habitat(s) or other abiotic and/or biotic factors (see above) are used or required by the Element, but these key requirements are common and within the generalized range of the species within the area of interest.

    CommentNarrow specialist. Relies on mature mesic forest types and riparian forests and often most abundant in areas with more closed canopy.

    Raw Conservation Status Score

    Score 3.5 + 0.25 (population size) + 0.0 (geographic distribution) - 0.5 (short-term trend) - 0.75 (threats) = 2.5
    How Scores are Calculated

 
General Description
We do not yet have descriptive information on this species.  Please try the buttons above to search for information from other sources.

General Distribution
Montana Range



Western Hemisphere Range

 


Summary of Observations Submitted for Montana
Number of Observations: 3608

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density

Recency

Breeding
(direct evidence "B")


Breeding
(indirect evidence "b")


No evidence of Breeding
(transient "t")


Overwintering
(regular observations "W")


Overwintering
(at least one obs. "w")



 

(Records associated with a range of dates are excluded from time charts)



Ecological Systems Associated with this Species
  • Details on Creation and Suggested Uses and Limitations
    How Associations Were Made
    We associated the use and habitat quality (high, medium, or low) of each of the 82 ecological systems mapped in Montana for vertebrate animal species that regularly breed, overwinter, or migrate through the state by:
    1. Using personal observations and reviewing literature that summarize the breeding, overwintering, or migratory habitat requirements of each species (Dobkin 1992, Hart et al. 1998, Hutto and Young 1999, Maxell 2000, Foresman 2001, Adams 2003, and Werner et al. 2004);
    2. Evaluating structural characteristics and distribution of each ecological system relative to the species’ range and habitat requirements;
    3. Examining the observation records for each species in the state-wide point database associated with each ecological system;
    4. Calculating the percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system to get a measure of “observations versus availability of habitat”.
    Species that breed in Montana were only evaluated for breeding habitat use, species that only overwinter in Montana were only evaluated for overwintering habitat use, and species that only migrate through Montana were only evaluated for migratory habitat use.  In general, species were associated as using an ecological system if structural characteristics of used habitat documented in the literature were present in the ecological system or large numbers of point observations were associated with the ecological system.  However, species were not associated with an ecological system if there was no support in the literature for use of structural characteristics in an ecological system, even if point observations were associated with that system.  High, medium, and low habitat quality was assigned based on the degree to which the structural characteristics of an ecological system matched the preferred structural habitat characteristics for each species in the literature.  The percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system was also used to guide assignments of habitat quality.  If you have any questions or comments on species associations with ecological systems, please contact Bryce Maxell at bmaxell@mt.gov or (406) 444-3655.

    Suggested Uses and Limitations
    Species associations with ecological systems should be used to generate potential lists of species that may occupy broader landscapes for the purposes of landscape-level planning.  These potential lists of species should not be used in place of documented occurrences of species (this information can be requested at: http://mtnhp.org/requests/default.asp) or systematic surveys for species and evaluations of habitat at a local site level by trained biologists.  Users of this information should be aware that the land cover data used to generate species associations is based on imagery from the late 1990s and early 2000s and was only intended to be used at broader landscape scales.  Land cover mapping accuracy is particularly problematic when the systems occur as small patches or where the land cover types have been altered over the past decade.  Thus, particular caution should be used when using the associations in assessments of smaller areas (e.g., evaluations of public land survey sections).  Finally, although a species may be associated with a particular ecological system within its known geographic range, portions of that ecological system may occur outside of the species’ known geographic range.

    Literature Cited
    • Adams, R.A.  2003.  Bats of the Rocky Mountain West; natural history, ecology, and conservation.  Boulder, CO: University Press of Colorado.  289 p.
    • Dobkin, D. S.  1992.  Neotropical migrant land birds in the Northern Rockies and Great Plains. USDA Forest Service, Northern Region. Publication No. R1-93-34.  Missoula, MT.
    • Foresman, K.R.  2001.  The wild mammals of Montana.  Special Publication No. 12.  Lawrence, KS: The American Society of Mammalogists.  278 p.
    • Hart, M.M., W.A. Williams, P.C. Thornton, K.P. McLaughlin, C.M. Tobalske, B.A. Maxell, D.P. Hendricks, C.R. Peterson, and R.L. Redmond. 1998.  Montana atlas of terrestrial vertebrates.  Montana Cooperative Wildlife Research Unit, University of Montana, Missoula, MT.  1302 p.
    • Hutto, R.L. and J.S. Young.  1999.  Habitat relationships of landbirds in the Northern Region, USDA Forest Service, Rocky Mountain Research Station RMRS-GTR-32.  72 p.
    • Maxell, B.A.  2000.  Management of Montana’s amphibians: a review of factors that may present a risk to population viability and accounts on the identification, distribution, taxonomy, habitat use, natural history, and the status and conservation of individual species.  Report to U.S. Forest Service Region 1.  Missoula, MT: Wildlife Biology Program, University of Montana.  161 p.
    • Werner, J.K., B.A. Maxell, P. Hendricks, and D. Flath.  2004.  Amphibians and reptiles of Montana.  Missoula, MT: Mountain Press Publishing Company. 262 p.

Reproductive Characteristics
Active nests are seen as early as mid-June, and fledged young as early as June 25.

References
  • Additional ReferencesLegend:   View WorldCat Record   View Online Publication
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    • American Ornithologists' Union. 1998. Check-list of North American birds. 7th edition. American Ornithologists' Union, Washington, D.C. 829 pp.
    • Casey, D. 2000. Partners in Flight Draft Bird Conservation Plan Montana. Version 1.0. 287 pp.
    • Ehrlich, P., D. Dobkin, and D. Wheye. 1988. The birder’s handbook: a field guide to the natural history of North American birds. Simon and Schuster Inc. New York. 785 pp.
    • George, T. Luke. 2000. Varied Thrush (Ixoreus naevius). Species Account Number 541. The Birds of North America Online (A. Poole, Ed.). Ithaca, NY: Cornell Laboratory of Ornithology; Retrieved 3/25/2008 from The Birds of North America Online database
    • Hejl, S.J., R.L. Hutto, C.R. Preston, and D.M. Finch. 1995. Effects of silvicultural treatments in the Rocky Mountains. In: T. E. Martin and D. M. Finch, eds. Ecology and Management of Neotropical Migratory Birds. Oxford Univ. Press, New York. pp.220-244.
    • Hutto, R. L. 1995. Composition of bird communities following stand-replacement fires in Northern Rocky Mountain (U.S.A.) conifer forests. Conservation Biology 9: 1041-1058.
    • Hutto, R. L. and J. S. Young. 1999. Habitat relationships of landbirds in the Northern Region, USDA Forest Service. General Technical Report RMRS-GTR-32. U. S. Department of Agriculture, Forest Service, and Rocky Mountain Research Station, Ogden, UT. 72 pp.
    • Johnsgard, P. A. 1992. Birds of the Rocky Mountains with particular reference to national parks in the northern Rocky Mountain region. Lincoln: University of Nebraska Press. xi + 504 pp.
    • Lenard, S., J. Carlson, J. Ellis, C. Jones, and C. Tilly. 2003. P. D. Skaar's Montana Bird Distribution, 6th Edition. Montana Audubon: Helena, MT, 144 pp.
    • Mannan, R.W. and E.C. Meslow. 1984. Bird populations and vegetation characteristics in managed and old-growth forests, northeastern Oregon. J. Wildl. Manage. 48(4): 1219-1238.
    • Montana Bird Distribution Committee. 2012. P.D. Skaar's Montana bird distribution. 7th Edition. Montana Audubon, Helena, Montana. 208 pp. + foldout map.
    • Salt, W.R. and J.R. Salt. 1976. The birds of Alberta. Hurtig Publishers, Edmonton, Alberta. xv + 498 pp.
    • Terres, J.K. 1980. The Audubon Society encyclopedia of North American birds. Alfred A. Knopf, New York. 1109 pp.
    • Tobalske, B.W., R.C. Shearer, and R.L. Hutto. 1991. Bird populations in logged and unlogged western larch/Douglas-fir forest in northwestern Montana. Res. Pap. INT-442. Ogden, UT: U.S.D.A. Forest Service, Intermountain Research Station. 12pp.
    • U.S. Forest Service. 1991. Forest and rangeland birds of the United States: Natural history and habitat use. U.S. Department of Agriculture, Forest Service Agricultural Handbook 688. 625 pages.
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Citation for data on this website:
Varied Thrush — Ixoreus naevius.  Montana Field Guide.  Montana Natural Heritage Program and Montana Fish, Wildlife and Parks.  Retrieved on September 29, 2014, from http://FieldGuide.mt.gov/speciesDetail.aspx?elcode=ABPBJ22010
 
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