The Blue-Grey Gnatcatcher (Polioptila caerulea) is a tiny (10 cm), active songbird in the Polioptilidae family, a family found throughout much of North and Central America, closely related to the Wrens (Troglodytidae). It is the most widespread member of its genus, distributed throughout North America from southwestern Ontario to Florida, California, and south to Honduras. Blue-Grey Gnatcatchers breeding in the Great Lakes Region are migratory, wintering in along the Gulf Coast, Mexico, and Mesoamerica. Here, they are observed between late April and late September. In the southern portion of its distribution, many Gnatcatchers are year-round residents. Other gnatcatcher species found in North America include the Black-tailed Gnatcatcher (Polioptila melanura) of the southwestern North American desert areas, and the California Gnatcatcher (Polioptila californica), a threatened species of southern California’s coastal sage scrublands.
The Blue-Grey Gnatcatcher prefers open deciduous woodlands, forest edges, scrublands, shrubby wetlands, riparian areas, and urban parks, especially those with widely spaced trees or near watercourses. They are less commonly found in dense forests. While being among the smallest of all native songbirds, Gnatcatchers are relatively easy to detect in spring and summer – the males produce persistent buzzy calls and high-pitched songs consisting of a series of variable, thin, wheezy notes and whistles. Male birdsong is primarily used for both territory defense and attracting a female mate. Calls are sharp, nasal sounds, described as a soft “spee” or “zhee”.
Blue-Grey Gnatcatchers typically raise 1 or 2 broods per summer breeding season. The female Gnatcatcher builds a small, woven cup-shaped nest placed on a horizontal tree limb well above the ground. The male Gnatcatcher provides the nesting material, which consists of lichens, bark strips, and spiderwebs. Nests are often camouflaged by lichen and bark, making them difficult to spot. Each clutch contains between 3–5 pale blue eggs with reddish or brown speckles. The female incubates the eggs for around 13 days, subsequently, both parents feed the young, which fledge between 10–15 days after hatching.
As their name implies, Gnatcatchers are insectivores, primarily feeding on small flying insects and other invertebrates during the breeding season. Commonly consumed insects include gnats, mosquitoes, flies (Diptera), small caterpillars and moths (Lepidoptera), aphids and true bugs (Hemiptera), beetles (Coleoptera), and spiders (Araneae). They forage by flitting actively among leaves and branches, often hovering briefly or sallying into the air to snatch prey. During late summer and autumn migration, Blue-Grey Gnatcatchers consume small berries, such as dogwood (Cornus sp.), elderberry (Sambucus sp.), viburnum fruits (Viburnum sp.), hawberries (Crataegus sp.), cherries (Prunus sp.), and pokeweed (Phytolacca americana).
The Blue-Grey Gnatcatcher is among the most successful bird species in North America – some expert ornithologists estimate that their population is over 300 million strong. Gnatcatchers have benefited from the proliferation of open forest and mosaic habitats following the clearing of dense forests throughout their distribution. Though many of these forests have since regenerated, providing habitat for woodland species, semi-open habitats preferred by Gnatcatchers remain abundant. It is considered a common breeder and migrant in the Great Lakes region and is a welcome spring arrival, signaling the return of other small songbirds such warblers, vireos, and flycatchers.
Written by Matthew Palarchio, HBSc in Environmental Sciences, Western University
All photos are Stock photos retrieved from Canva
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