With summer upon us, some of the brightest colored birds in North America are nesting all across the country including the Midwest. Two of these birds that can be somewhat difficult to tell apart without knowing the field markings are the Blue Grosbeak and the Indigo Bunting. Both of these species are bright blue, frequently overlap in geographic range, and can be found around the same habitat. This means birders are likely to encounter both at some point. The good news is that there are some surefire ways to differentiate the two.
Size
As far as size is concerned, there is a discernible difference between a Blue Grosbeak and an Indigo Bunting. Blue Grosbeaks typically range between 15 and 16 cm while Indigo Buntings are between 12 and 13 cm. This means that in theory, an Indigo Bunting should never be as large as even a relatively small Blue Grosbeak. While it is hard to tell size on a single bird by itself, a side by side comparison shows this difference distinctly.
Range
The range of these two species differs slightly with much of it overlapping.
Blue Grosbeaks general range is as far south as Central America during the winter months and as far north as North Dakota in summer. They span from the west coast to the east coast and can be found readily in the southern states. While the Blue Grosbeak is widespread in the United States, their basic range does not typically go north of Colorado and Indiana with only a few individuals spotted annually during summer in states like Wisconsin. They do however appear farther north in the central part of the United States as they also summer in Oklahoma and the Dakotas.
Much like the Blue Grosbeak, Indigo Buntings winter as far south as Central America. This bright blue bird also inhabits most of the southern United States with the exception of parts of Arizona and Texas. It is also notable to note that the Indigo Buntings range seems to skip over western Mexico. Unlike Blue Grosbeaks, Indigo Buntings make their way much farther north in summer as they are found in every state east of Montana and even southern parts of Canada.
Bill
Bill size is a solid way to differentiate between these two species. The indigo Bunting has a relatively small, conical bill while the Blue Grosbeak has a comparatively larger bill. In addition, The Indigo Bunting has a completely one colored gray/silver bill. The Blue Grosbeak often sports a two colored bill with a darker gray on the upper mandible and lighter gray on the bottom mandible.
Field Markings
Though both of these birds are a very similar shade of blue, there are some differences in pattern and coloration that go a long way in identification.
The Blue Grosbeak has a small black mask near the base of the bill going over the eye that the Indigo Bunting lacks. They also have very distinctive rusty wing bars that serve as an extremely reliable field marking. Female Blue Grosbeaks lack the deep blue of the males (instead they are a dark tan/light brown color) but still have the same rust colored wing bars.
Indigo Buntings are almost entirely blue with some of their only other coloring being a varied gray to black on their wings. They do have a very small amount of black near the base of the bill but not nearly to the degree that the Blue Grosbeak does. Females are a lighter shade of tan than the Blue Grosbeak and lack the wing bars of the Blue Grosbeak females.
These two species often co-exist in the same habitat and overlap readily in the United States and Mexico. Even in ranges where only one of these species would be expected. It is good to know the ways to tell them apart just in case.
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