Montana Field Guide

Blue-gray Gnatcatcher - Polioptila caerulea

The Blue-gray Gnatcatcher is a very small (10.0 to 11.5 cm in length, 5 to 7 grams in weight), bluish-gray, long-tailed songbird; tail length constitutes about 45% of the total length. The bill is fine-tipped and narrow with a slight lateral flattening at the base, which is surrounded by prominent rictal bristles. Upperparts are medium plumbeous mixed with ultramarine, and there is a prominent white eye-ring. Males in alternate plumage show a narrow black line over the bill and extending over and behind the eyes. Underparts are white, and the tail is black with outer retrices edged in white. The tail is frequently fanned and waved, showing the white edging. Females appear slightly paler (grayer) overall (Ellison 1992).

Montana Range

Breeding birds in Montana migrate out of state for the winter. Over-wintering locations have not been identified for Montana breeders.

Breeding habitat in Montana is restricted to open stands of Utah juniper (Juniperus osteosperma) and limber pine (Pinus flexilis) with intermixed big sage (Artemisia tridentata). All nests found have occurrred 0.8 to 1.7 meters above ground in Utah juniper or big sage growing on the lower slopes or bottoms of canyons (P. Hendricks unpublished data).

Throughout their range Blue-gray Gnatcatchers typically inhabit deciduous forest, riparian woodland, open woodland, second-growth, scrub, brushy areas and chaparral in the east, south, and coastal west (Tropical to lower Temperate zones) (AOU 1983, Ellison 1992). In the Great Basin region of the west they also occupy open pine woodland, where (in Wyoming) they are associated with rosaceous shrubs and rock outcrops (Pavlacky and Anderson 2001).

They nest especially where tracts of brush, scrub, or chaparral are intermixed with taller vegetation (e.g., forest edge, riparian corridors); nesting often occurs near water. Nests are built on branches or forks of trees or shrubs, usually 1 to 25 meters above ground (Harrison 1978) and both sexes participate in nest construction. A broad range of brushy habitats is occupied during winter (Ellison 1992).

Blue-gray Gnatcatchers feed on adult insects as well as their larvae and eggs, and also other arthropods (spiders, etc.). They forage by darting out from a perch and catching insects in the air, or by gleaning food from twigs and branches (Ellison 1992).

Breeding pairs establish a territory that the male defends, occasionally assisted by the female. In California, breeding territories averaged 1.8 hectares (n = 9), ranging from 0.9 to 3.0 hectares. In Vermont, mean size was 0.7 hectare (n = 4), ranging from 0.5 to 1.1 hectares (Ellison 1992).

Clutch size in Montana (n = 9 nests) is 4 to 5 eggs. Nest construction begins in late May, eggs are laid in early to late June, and nestlings are present from mid-June to mid-July. Both sexes incubate eggs and tend nestlings (P. Hendricks unpublished data). Nestlings are altricial and naked at hatching. Young are brooded and fed by both parents, and leave the nest in 13 (10 to 15) days (Ellison 1992). Fledged young with adults have been observed into early September on the breeding grounds (Wright 1996, P. Hendricks personal observation).

No management activity is currently underway. Grazing may have a negative impact by directly or indirectly altering habitat for nesting and foraging. Nest parasitism by Brown-headed Cowbirds has recently been documented in Montana (P. Hendricks unpublished data).