A few Blue Grosbeak's showed up at our feeders in April and stayed around a couple weeks. They were probably migrants, passing through on their way north. Blue Grosbeaks winter in central America and Mexico then migrate into the eastern U.S. during breeding season. Males arrive on the breeding grounds early in the season and form feeding flocks before females arrive.
I observed that the Blue Grosbeaks arrived about the same time as Indigo Buntings. Both of these groups intermingled often while feeding.
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.
Blue Grosbeaks are often easily confused with Indigo Buntings because they have similar colors. Blue Grosbeaks are also buntings, but they're larger than Indigo Buntings. The differences are noticed in the colors of their shoulders, faces and beaks. An adult, breeding Blue Grosbeak has chestnut colored wing bars, a tiny black mask in front of their eyes and a very large triangular black and silver bill that seems to cover the entire front of their face. Females are a rich, cinnamon brown with darker tones on the head and and paler on the underparts. They also have a bluish tint to their tails.
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. Most of the information here was gathered from allaboutbirds.org.