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Blue-gray Gnatcatcher

Polioptila caerulea ORDER: PASSERIFORMES FAMILY: POLIOPTILIDAE

IUCN Conservation Status: Least Concern

A tiny, long-tailed bird of broadleaf forests and scrublands, the Blue-gray Gnatcatcher makes itself known by its soft but insistent calls and its constant motion. It hops and sidles in dense outer foliage, foraging for insects and spiders. As it moves, this steely blue-gray bird conspicuously flicks its white-edged tail from side to side, scaring up insects and chasing after them. Pairs use spiderweb and lichens to build small, neat nests, which sit on top of branches and look like tree knots.

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At a GlanceHelp

Measurements
Both Sexes
Length
3.9–4.3 in
10–11 cm
Wingspan
6.3 in
16 cm
Weight
0.2–0.2 oz
5–7 g
Relative Size
Slightly larger than a Ruby-throated Hummingbird, Slightly smaller than a House Wren.
Other Names
  • Gobemoucherons Gris-bleu (French)
  • Perlita Común, Perlita Grisilla (Spanish)

Cool Facts

  • The Blue-gray Gnatcatcher's grayish coloring and long tail, as well as the way it mixes snippets of other birds' repertoires into its own high, nasal songs, have earned it the nickname "Little Mockingbird."
  • The Blue-gray Gnatcatcher is the northernmost-occurring species of gnatcatcher, and the only truly migratory one. Most members of its genus are resident in Central and South America.
  • The nesting range of Blue-gray Gnatcatchers has been shifting northward since the early twentieth century. Over the last quarter of that century, the shift was about 200 miles, in concert with increasing average temperatures.
  • A pair of Blue-gray Gnatcatchers can build up to seven nests in a breeding season. They often re-use nest material from previous nests, which speeds re-nesting. This can be essential to breeding success, since predation, nest parasitism, or mite infestations frequently cause nest loss and brood failure.
  • Occasionally, significant numbers of Blue-gray Gnatcatchers "overshoot" on their spring migrations and end up much further north than usual. They may be carried past their target by strong southwest winds in warm regions, and by strong northerly winds on the west side of high pressure systems. Most probably make their way back south before nesting.
  • In spite of their name, gnats do not form a significant part of the Blue-gray Gnatcatcher's diet.
  • Fiercely territorial Blue-gray Gnatcatchers may use vocal displays and postures to chase a rival as far as 70 feet. Further resistance by an intruder may provoke midair confrontations, with the two birds climbing steeply, breast-to-breast, snapping at each other.
  • The oldest known Blue-Gray Gnatcatcher was at least 3 years and 3 months old, and estimated to be at least 4 years, 2 months old, when it was caught at a banding station in Pennsylvania and rereleased.

Habitat


Forest

Blue-gray Gnatcatchers nest and forage in a broad range of wooded habitats across their extensive breeding range. Although they shun coniferous forests lacking rich understory growth, they use a range of broadleaf and mixed woodlands from chaparral to mature forests. They prefer moist areas, often near habitat edges. In the northernmost parts of their range, they nest along rivers and streams or near lakes, particularly in ash, maple, and oak forests. In the Southwest, oak and pinon-juniper woodlands, chaparral, and willow and cottonwood woodlands near water all provide habitat. Throughout the south-central and mid-Altantic states, they claim territories in upland broadleaf and mixed forests as well as along streams and rivers. Farther south, they add swamp forests and pine flatwoods with oak understory. They favor the edges of forest gaps, so extensive patch-cut logging can provide abundant habitat. Their winter habitats are similarly various from region to region, and may include cypress swamps, citrus orchards, mangroves, savannah with scattered groves, and a range of woodlands from sea level swamp forests to highland oaks.

Food


Insects

Blue-gray Gnatcatchers eat small insects, spiders, and other invertebrates. Prey species vary across their extensive range. In the Southwest, for example, prey include treehoppers, froghoppers, leaf hoppers, plant bugs, tree bugs, leaf beetles, weevils, wolf spiders, caterpillars, and grasshoppers. In the Northeast, adult and larval moths can provide up to half of prey taken. The smallest prey are swallowed alive. The wings are torn off larger prey and their bodies beaten on a perch prior to being eaten. Parents generally feed the young these same foods, offering progressively larger whole prey as the chicks mature.

Nesting

Nesting Facts
Clutch Size
3–5 eggs
Number of Broods
1-2 broods
Egg Length
0.5–0.6 in
1.3–1.6 cm
Egg Width
0.4–0.5 in
1.1–1.2 cm
Incubation Period
11–15 days
Nestling Period
10–15 days
Egg Description
Pale blue spotted with reddish to dark brown.
Condition at Hatching
Born naked and helpless, with eyes closed and little movement.
Nest Description

Both sexes cooperate in building the neat, open, cuplike nest. They take up to two weeks to build the 2–3-inch wide nest, which is held together and attached to its branch with spider webbing and decorated with lichen. The nest's high walls are built in flexible layers. The main structural layer is built of fibrous materials like plant stems, bark strips, and grasses, all held together by spiderweb or caterpillar silk. Inner layers become progressively finer, and the roughly 1.5-inch-wide cup is lined with plant down, paper, cocoons, hair, or feathers. The outside is covered with webbing or silk decorated with bits of lichen or bark flakes. They often build a series of nests during a summer to counteract the effects of predation, mite infestations, or cowbird parasitism. Materials from earlier nests are frequently recycled to build later nests, which may be why they are usually completed more quickly than first nests. The male often builds second nests nearly solo, with the female finishing the inside of the first nest with softer materials.

Nest Placement

Tree

Male and female jointly choose a nest site, usually in a live broadleaf tree in a less dense bit of their territory. Nests are built well out on side limbs, often saddled against a side branch or around a twig or knot for support. Nests tend to be higher than the midpoint of the tree.

Behavior


Foliage Gleaner

The Blue-gray Gnatcatcher is a busy forager. It flits through dense outer foliage, hops and sidles along branches, peering with quick head movements to glean small insects and spiders. Flashing the white edges of their long tail may help them flush prey, which they then snap up while the gnatcatcher is perched, hovering, or sallying into the air after them. Pairs bond quickly on the breeding ground, with the male's initial aggression toward intruders softening as he leads the female around the territory. They explore possible nesting sites together, with one or the other occasionally mimicking nest-building. These gnatcatchers are pugnacious defenders of their territories, attacking much larger birds as well as intruding neighbors. Adults mob potential predators with other small birds. The male and female of a pair often cooperate in challenging an interloper. The male's soft territorial songs and the female's aggressive calls quickly turning to extended chase, usually by the male. More intense aggression involves soaring aerial confrontation and bill snapping, and even prolonged grappling on the ground. Although the female does most of the brooding, the male shares nest-building, incubation, and the feeding of nestlings and fledglings. While there seems to be little predation on adults, nestlings and eggs are taken by jays, magpies, and woodpeckers, and probably by snakes, crows, grackles, raccoons, squirrels, and chipmunks.

Conservation

status via IUCN

Least Concern

Blue-gray Gnatcatchers are numerous and their overall populations have been growing at almost 1 percent per year since 1966, according to the North American Breeding Bird Survey. Growth appears to have been particularly strong in the West. Partners in Flight estimates a global breeding population of 160 million, with 74 percent breeding in the U.S. and 65 percent spending some part of the year in Mexico. They rate a 7 out of 10 on the Continental Concern Score and are not on the 2012 Watch List. The largest populations are in the southeastern U.S. Despite their high numbers, nests are very vulnerable to cowbird parasitism. Adult gnatcatchers attack intruding cowbirds, but once a cowbird has laid an egg in their nest, these tiny birds have no ability to eject or puncture it.

Credits

Range Map Help

Blue-gray Gnatcatcher Range Map
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Migration

Resident to long-distance migrant. Northern breeders are long distance migrants. Most southerly birds are short distance migrants, and some are year-round residents.

Find This Bird

Blue-gray Gnatcatchers are widespread but not abundant. The nasal, wheezy, rambling song and insistent, squeaky calls are great first clues to finding them, particularly as these tiny birds can get lost in the generally taller habitats used in the eastern part of their range. It’s a bit easier to find gnatcatchers in the West because they tend to occur in shorter, more open habitat. During fall migration, eastern Blue-gray Gnatcatchers can accumulate on the Gulf Coast, particularly the Texas coast, in huge numbers.