During their breeding season in North America they eat insects, seeds of grasses and herbs, and berries. In winter they eat seeds, buds, and some insects found in their tropical environment. Since many of the birds like the habitat of open fields, they have been found eating rice in rice fields. When Indigo Buntings return to the breeding grounds of North America, they usually breed a few kilometers away from their natal area. They come to the breeding grounds in late April to early June.
Indigo buntings settle on a territory in pairs a few days after arriving at the breeding grounds.
Before mating, the male flies to the female and mounts her from behind actually making vent contact for about two seconds. During copulation, the male makes a buzzing sound, flies away from the female as she calls back and quivers her wings while lifting her tail up. They repeat the copulations 4-10 times in ten minutes. The pair interacts with each other till the female bunting begins incubation. Without the male's help, the female chooses the site and builds the nest on her own.