Blue Grosbeak Life History

Habitat

Habitat Open WoodlandsBlue 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.Back to top

Food

Food InsectsAlthough 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.Back to top

Nesting

Nest Placement

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

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.

Nesting Facts
Clutch Size:3-5 eggs
Number of Broods:1-2 broods
Egg Length:0.8-0.9 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.
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Behavior

Behavior Foliage GleanerMales 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.Back to top

Conservation

Conservation Low ConcernBlue Grosbeaks are uncommon but widespread across the southern United States. Their overall population is stable, and slightly increased between 1966 and 2014, according to the North American Breeding Bird Survey. Partners in Flight estimates their global breeding population at 24 million, with 74% spending some part of the year in the U.S. and 57% in Mexico. They rate an 8 out of 20 on the Continental Concern Score and are not on the 2014 State of the Birds 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.Back to top

Backyard Tips

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

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Credits

Lowther, Peter E. and James L. Ingold. 2011. Blue Grosbeak (Passerina caerulea), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

Lutmerding, J. A. and A. S. Love. Longevity records of North American birds. Version 2015.2. Patuxent Wildlife Research Center, Bird Banding Laboratory 2015.

North American Bird Conservation Initiative. 2014. The State of the Birds 2014 Report. US Department of Interior, Washington, DC, USA.

Partners in Flight (2017). Avian Conservation Assessment Database. 2017.

Sauer, J. R., J. E. Hines, J. E. Fallon, K. L. Pardieck, Jr. Ziolkowski, D. J. and W. A. Link. The North American Breeding Bird Survey, results and analysis 1966-2013 (Version 1.30.15). USGS Patuxtent Wildlife Research Center 2014b. Available from http://www.mbr-pwrc.usgs.gov/bbs/.

Sibley, D. A. (2014). The Sibley guide to birds, second edition. Alfred A. Knopf, New York, USA.

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