However, it's also worth noticing the relatively large head and short tail, and the black area that extends from the base of the bill back around the eye. Although Blue Grosbeak is found mainly in the South and Indigo Bunting mainly in the East, both occur so widely that observers in many regions will encounter them, either as expected species or as rarities. Birders who see both species regularly may be able to distinguish them at a glance. For others, though, a review of their field marks is worthwhile, especially since some of their standard field marks can be misleading. However, buntings of both sexes may bend this rule.
Male indigos are blue only in breeding plumage and mostly rich brown during the winter.
When they are molting from one plumage to another, they may be mostly blue with some brown in the wings, sometimes enough to suggest the grosbeak's wing bars. Female Indigo Buntings usually show some fine streaking or mottling on the chest. If chest streaking is noticed, it provides a good distinction from female Blue Grosbeaks. With practice, the key to separating these species is seeing the difference in their shapes. Blue Grosbeaks are much more interesting in shape.