Montana Field Guide

The Warbling Vireo is highly noted for its persistent singing - even from the nest. It is a small gray-olive bird with white underparts sometimes slightly washed yellow. Length 12-13 cm, body mass 10-16 g. Face with moderately distinct white supercilium contrasting indistinctly with grayish eye-line, but otherwise very plain, without additional contrasting markings. Sexes alike and plumages similar throughout year. (Gardali, Thomas, and Ballard, Grant. The Birds of North America, No. 551, 2000).

In the Bozeman area, normal migration periods are May 22 to June 10 and August 25 to September 8.

Throughout range, shows a strong association with mature mixed deciduous woodlands especially along streams, ponds, marshes, and lakes but sometimes in upland areas away from water. Also found in young deciduous stands that emerge after a clear-cut. In general, overall habitat structure consists of large trees with semi-open canopy. Other habitats include urban parks and gardens, orchards, farm fencerows, campgrounds, deciduous patches in pine forests, mixed hardwood forests, and rarely, pure coniferous forests (Gardali and Ballard 2000).

Insects, throughout the year. Some fruit in winter (Gardali and Ballard 2000).

Territory sizes of 3.4 to 5.6 acres in Douglas fir forests in western Montana have been recorded.

Builds nest in the forked limbs of trees from 1 to 40 meters above the ground. Nest is a rough and slightly rounded hanging cup, usually suspended from forks of horizontal twigs. Eggs are usually ovate in shape, white in color marked sparingly, smooth and without gloss. Clutch size ranges 1 to 5, usually 3 or 4 eggs (Gardali and Ballard 2000). Near Fortine, egg dates range from June 25 to July 15. Statewide, it nests during July and early August.