Small, 13 to 15.2 cm, 9.3 to 11.4 g. Sexually monomorphic. Upperparts grayish olive to grayish brown; underparts mostly whitish with a varying amount of yellow wash; throat whitish; outer tail feathers have whitish edges. Conspicuous eye-ring which may extend forward to the lores, appearing almost as spectacles in some. Wing bars usually whitish and fairly narrow. Bill is mostly dusky in adults (pale orangish at base of lower mandible) (Sedgwick 1993).
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.
Western Hemisphere Range
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The Bozeman area migration periods are from May 16 to June 10 and August 15 to September 15, with no spring peak. The fall peak is September 5 (Skaar 1969).
Inhabits open coniferous forest, mountain chaparral, aspen groves, streamside willow thickets and brushy open areas (Sedgwick 1993). In Montana, brushy, logged over slopes seem to be favored habitat (Johnsgard 1986).
Primarily an aerial forager - a sit and wait predator. It eats flying insects, occasionally pounces on prey on the ground (Sedgwick 1993).
Western Montana territory size in Douglas-fir forests is 4.0 to 4.3 acres. Nests have been found parasitized by Brown-headed Cowbirds. 46% and 31% of singing and non-singing perches were in the upper 1/3 of mature conifers.
In western Montana nests were in small bush crotches; the average nest height was 5 feet; the nestling period was 16 to 17 days; 40% of the eggs survived to fledging; an average of 2.7 young were reared per successful nest, and nest dates were mid-June to late July (Davis 1961). Fortine egg dates are June 14 to July 20.