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Montana Field Guide

Montana Field Guides

Cassin's Vireo - Vireo cassinii

Native Species

Global Rank: G5
State Rank: S4B
(see State Rank Reason below)


Agency Status
USFWS: MBTA
USFS:
BLM:
FWP SWAP: SGCN
PIF: 3


 

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Copyright by Borror Laboratory of Bioacoustics, Department of Evolution, Ecology, and Organismal Biology, Ohio State University, Columbus, OH, all rights reserved.
State Rank Reason (see State Rank above)
Species is found in forested habitats across western Montana. Populations appear stable. It faces moderate threats from nest parasitism by Brown-headed Cowbird.
Cassin's Vireo (Vireo cassinii) Conservation Status Summary
State Rank: S4B
Review Date = 10/16/2025
See the complete Conservation Status Rank Report
How we calculate Conservation Status Ranks
 
General Description
Sexes monomorphic by plumage and size, although females tend to be slightly duller. Upperparts dull olive-green becoming brownish gray on crown and auriculars. Brownish-gray face contrasts with bold, white “spectacles,” formed by supraloral stripe and eye-ring, the latter interrupted by dusky loral streak. Wings and tail brownish black; 2 broad yellowish-white wing-bars. Remiges and rectrices finely edged olive-yellow or grayish olive; outer rectrix finely edged white. Rump brighter olive-green than mantle. Underparts dingy white with sides of breast smudged dull olive-green, and paler, yellowish-olive flanks. Iris brown; bill black with bluish-gray base; legs grayish blue (Goguen and Curson 2002).

For a comprehensive review of the conservation status, habitat use, and ecology of this and other Montana bird species, please see Marks et al. 2016, Birds of Montana.

Species Range
Montana Range Range Descriptions

All Ranges
Summer
Migratory
(Click legend blocks to view individual ranges)

Western Hemisphere Range

 


Observations in Montana Natural Heritage Program Database
Number of Observations: 12757

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

Recency

SUMMER (Feb 16 - Dec 14)
Direct Evidence of Breeding

Indirect Evidence of Breeding

No Evidence of Breeding

WINTER (Dec 15 - Feb 15)
Regularly Observed

Not Regularly Observed


 

(Observations spanning multiple months or years are excluded from time charts)



Habitat
Species tends to prefer dry, open forests. Occupies coniferous, mixed-coniferous/deciduous, and deciduous forests in mountains and foothills.

National Vegetation Classification System Groups Associated with this Species

Food Habits
Diet consists almost exclusively of arthropods, spring through autumn. Winter diets consists of fleshy fruits.

Reproductive Characteristics
Clutch size of three to five eggs (usually four). Incubation period 13 to 14 days.


References
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Citation for data on this website:
Cassin's Vireo — Vireo cassinii.  Montana Field Guide.  .  Retrieved on , from