When I think of blackbirds, I think of the red-winged and yellow-headed species that spend their summers in wetlands defending territory and weaving their nests in the reeds close to water. Bobolinks are a different subset of the blackbird family in that they defend territories and site their nests on the upland ground of grasslands.
According to All About Birds:
Bobolinks breed in open areas across the northern United States and southern Canada, preferring large fields with a mixture of grasses and broad-leaved plants like legumes and dandelions. They formerly nested mainly in tallgrass and mixed prairie of the midwestern United States and south-central Canada. They now also nest in eastern hayfields and meadows, which became available as eastern forests were cleared, and west of the Great Plains in recently irrigated habitats. After breeding, Bobolinks move to freshwater marshes and coastal areas to molt before migrating. Their main wintering area is in the southern interior of South America, where they spend their time in grasslands, marshes, rice fields, and sorghum fields.
What is incredible about these birds is how far they migrate in the winter - from All About Birds:
The Bobolink is one of the world’s most impressive songbird migrants, traveling some 12,500 miles (20,000 kilometers) to and from southern South America every year. Throughout its lifetime, it may travel the equivalent of 4 or 5 times around the circumference of the earth.
The Bobolink’s distinctive flight separates them from the red-winged when they are neighbors in adjoining habitats. The Bobolink has a weak flight that helicopters around in the air often singing its babbling song versus the Red-winged’s piercing call and direct flight to its destination.
Bobolink’s song from the xeno-canto.org website:
Bobolinks are endearing summer birds to those who have grown up in pastured farmland. They are plentiful with a breeding population of 10 million but have been declining rapidly like all grassland birds due to losses in large acres of undisturbed meadows, prairies and hay fields. One farming technique that is being promoted is to delay cutting hay fields during their nesting period. In Minnesota that is approximately from mid-May until the end of June.
Just saw my first Bobolink last week, sure enough sitting on a fence post of a grassy field.