Bobolink is one of only two North American bird species that go through two complete molts per year, explaining the completely different appearance of the males in spring and fall. Although placed in the blackbird family, it is quite a unique species in several respects.
Bobolinks winter in large flocks in south-central South America, where they are often known as the ricebird and can cause extensive damage to local rice crops. In spring, Bobolinks move north through the eastern Caribbean. Their main arrival is in mid-April and by early May the birds are territorial throughout much of the breeding range, singing and displaying in loose colonies from the Mid-Atlantic and New England west to the western Great Plains and northern Great Basin. These loose colonies struggle to pull off a brood of young before mowing and haying operations (or natural threats like drought or predation), but by mid-July a few birds may already be on the move back to the south.
The fall migration of Bobolink can be dramatic along the Atlantic coast, where hundreds or thousands of birds may gather in coastal meadows or marshlands. During fall they are often heard flying overhead giving their unique flight note, and experts detect the species regularly high overhead without even seeing the bird. Watch for the patterns of their southward movement fall, and especially their strong concentration on the Atlantic Coast in fall. There may be more to learn about even the broad patterns in a widespread species like this.