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.Back to top
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.Back to top
Blue Grosbeaks usually build their nests low in small trees, shrubs, tangles of vines, briars, or other vegetation, often near open areas or roads.
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.
|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.|
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.Back to top
Blue Grosbeaks are uncommon but widespread across the southern United States. Their overall population is stable, and increased over 0.7% per year between 1966 and 2019, according to the North American Breeding Bird Survey. Partners in Flight estimates their global breeding population at 35 million and rates them 8 out of 20 on the Continental Concern Score, indicating a species of low conservation concern. 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 due to the clearing of forests. 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
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. (2020). Longevity records of North American birds. Version 2020. Patuxent Wildlife Research Center, Bird Banding Laboratory 2020.
Partners in Flight. (2020). Avian Conservation Assessment Database, version 2020.
Sauer, J. R., D. K. Niven, J. E. Hines, D. J. Ziolkowski Jr., K. L. Pardieck, J. E. Fallon, and W. A. Link (2019). The North American Breeding Bird Survey, Results and Analysis 1966–2019. Version 2.07.2019. USGS Patuxent Wildlife Research Center, Laurel, MD, USA.
Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.