The Blue-gray Gnatcatcher is the most widespread member of its genus in North America and the only Polioptila found in cold temperate regions. It is also the only truly migratory gnatcatcher, although individuals breeding in Central America are largely resident.
These birds inhabit a wide range of wooded habitats but prefer moist areas with broad-leaved trees, often at or near habitat edges. They are active feeders that usually glean insects off foliage but also catch them by hovering and sallying after flushed prey. The calls and songs of this species are highpitched and nasal. The sexes are only weakly dimorphic and pair monogamously. Males contribute significantly to nesting attempts, including nest construction, incubation, and the feeding of nestlings and fledglings. Nests are neat and cup-like, held together with webbing and decorated with lichens, and usually built well out on side limbs and branches of trees or large shrubs. Populations of this species have increased over the past 25 years, expanding northward, most dramatically in the northeastern U.S. and southeastern Canada.
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