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Blue Grosbeak

Passerina caerulea ORDER: PASSERIFORMES FAMILY: CARDINALIDAE

IUCN Conservation Status: Least Concern

A large, vibrantly blue bunting with an enormous silver bill and chestnut wingbars, the male Blue Grosbeak sings a rich, warbling song from trees and roadside wires. He and his cinnamon-colored mate often raise two broods of nestlings in a single breeding season. A bird of shrubby habitats, these richly colored birds can be hard to spot unless you hear them singing first. They are widespread but not abundant across the southern U.S., and are expanding their range.

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At a GlanceHelp

Measurements
Both Sexes
Length
5.9–6.3 in
15–16 cm
Wingspan
11 in
28 cm
Weight
0.9–1.1 oz
26–31 g
Relative Size
Larger than an Indigo Bunting; slightly smaller than a Brown-headed Cowbird.
Other Names
  • Guiraca bleue (French)
  • Piquirgrueso azul, Ruiz azul grande (Spanish)

Cool Facts

  • According to genetic evidence, the Lazuli Bunting is the Blue Grosbeak’s closest relative.
  • In the southern part of the Blue Grosbeak’s breeding range, each mated pair may raise two broods of nestlings per year.
  • Many Blue Grosbeaks migrate directly southward from their breeding areas to their wintering grounds. Western birds head over land and eastern birds cross the Gulf of Mexico. Migrating grosbeaks pass through the Caribbean Islands including Puerto Rico, the Bahamas, the Turks and Caicos Islands, the Antilles, the Swan Islands, the Cayman Islands, and the Virgin Islands.
  • Blue Grosbeaks breed along roads and open areas, building their nests low in small trees, shrubs, tangles of vines, or briars. At least one pair of grosbeaks has nested in a bluebird nest box.
  • Blue Grosbeaks have expanded northward in the United States in the past century or two, possibly taking advantage of forest clearing.
  • The oldest Blue Grosbeak on record was 6 years, 1 month old when it was captured and released by a Maryland bird bander in 2010.

Habitat


Open Woodland

Blue Grosbeaks breed in tangled vine and shrub habitats across southern North America—as far north as New Jersey in the east, central California in the west, and North Dakota in the interior United States. These habitats may be in old fields, forest edges, transmission-line corridors, hedgerows, stream edges, deserts, mesquite savannas, saltcedar forests, and southern pine forests. Their habitat requirements seem to include a small number of tree species, little canopy coverage, and low shrub density. Blue Grosbeaks spend the winter in shrubby habitats of Mexico and Central America as far south as central Panama.

Food


Insects

Although they feed mostly on insects (especially grasshoppers and crickets), Blue Grosbeaks also eat other invertebrates such as snails, along with the seeds of wild and cultivated grains. Their insect diet includes beetles, bugs, cicadas, treehoppers, and caterpillars. The grain portion of their diet includes seeds of bristlegrass, panicgrass, wheat, oats, rice, corn, and alfalfa. They hover and glean food from foliage, sally out for flying insects from a perch, and even hunt for insects on the ground. Before feeding an insect to their nestlings, they remove the head, wings, and most of the legs.

Nesting

Nesting Facts
Clutch Size
3–5 eggs
Number of Broods
1-2 broods
Egg Length
0.7–0.9 in
1.9–2.4 cm
Egg Width
0.6–0.7 in
1.6–1.7 cm
Incubation Period
12–13 days
Nestling Period
9–10 days
Egg Description
Pale blue to white, and on rare occasions spotted with brown.
Condition at Hatching
Helpless, with brownish gray down and closed eyes.
Nest Description

The female probably does most of the construction, but males sometimes build nests as well. The compact, cup-shaped nest is woven from twigs, bark strips, rootlets, cotton, rags, newspaper, string cellophane, snakeskin, dead leaves, or other materials. The inner cup measures 2–3 inches across and about 2 inches deep, and is often lined with rootlets, hair, and fine grasses.

Nest Placement

Shrub

Blue Grosbeaks usually build their nests low in small trees, shrubs, tangles of vines, briars, or other vegetation, often near open areas or roads.

Behavior


Ground Forager

Males arrive on the breeding grounds early in the season and form feeding flocks before females arrive. Each breeding pair defends a territory 2-20 acres in size during nest building and incubation, allowing the territory to shrink once the nestlings hatch. They are probably monogamous, and each pair may raise two broods together in a single breeding season. Blue Grosbeaks are heavily parasitized by cowbirds, which lay their own eggs in the grosbeak’s nests. Young birds and adults gather in large flocks to feed in grain fields, grasslands, and rice fields before migrating to their wintering grounds.

Conservation

status via IUCN

Least Concern

Blue Grosbeaks are uncommon but widespread across the southern United States. Their overall population grew by about 1 percent per year from 1966–2010, according to the North American Breeding Bird Survey. Partners in Flight estimates their global breeding population at 24 million, with 74 percent breeding in the U.S. and 57 percent spending some part of the year in Mexico. They rate an 8 out of 20 on the Continental Concern Score and are not on the 2012 Watch List. Even in the nineteenth century, naturalists reported that Blue Grosbeaks lived in low densities. The breeding range expanded northward in the late nineteenth and early twentieth century, possibly because of forest cutting. Blue Grosbeaks live at the greatest densities (about 80 breeding males per square mile) in mature longleaf pine forests of Florida and mixed loblolly-shortleaf pine forests in eastern Texas. The effects of agriculture and deforestation on their wintering grounds are unknown. On their breeding grounds, they may benefit from some current land-use trends but not others: they thrive in abandoned agricultural land, for instance, but avoid suburban habitats.

Credits

Range Map Help

Blue Grosbeak Range Map
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Migration

Long-distance migrant. Most individuals that nest in the eastern United States probably fly across the Caribbean to reach their wintering grounds, while western individuals may migrate over land.

Backyard Tips

Blue Grosbeaks may be attracted to grains and seeds at feeders in shrubby backyards.

Find This Bird

Though never common during summer and despite its generally retiring habits, the openness of Blue Grosbeak habitat and the males’ propensity for singing from high, exposed perches should enable you to locate it in most of its range. Learning and listening for their burry, warbling songs makes locating Blue Grosbeaks much easier. Be sure to continue to check likely looking shrubby or old-field habitat, even if they seem to be absent in early summer—many individuals arrive quite late, even deep into July, when Blue Grosbeak can be one of the few singing birds in such habitats.