What visual feature causes the transformation of the Bobolink across seasons to be considered one of the most dramatic shifts among North American songbirds?

Answer

Sexual dichromatism coupled with complete seasonal reversal

The uniqueness of the Bobolink plumage lies in the profound sexual dichromatism governing the species, coupled with the complete seasonal reversal undertaken by the male, allowing the bird to essentially wear two different outfits.

What visual feature causes the transformation of the Bobolink across seasons to be considered one of the most dramatic shifts among North American songbirds?
animalPlumageBobolink