After overwintering in the southern hemisphere, vast, generally single-sex, flocks of bobolinks undergo an approximately 10,000 kilometre journey—one of the longest migrations of all New World passerines—to the North American nesting grounds (2). In order to navigate across such a vast distance, the birds are believed to use the magnetic field of the Earth, as well as the positions of the stars. The journey begins in early Match and may take over two months to complete, with most individuals arriving at the nesting grounds in May (2) (3).
After arriving at the nesting grounds, male bobolinks establish territories, and begin to compete for the attention of the females, a process which involves song, ritualized display, fighting, and male-male chases (2). Interestingly, male bobolinks may form breeding pairs with up to four females simultaneously, a breeding arrangement known as polygyny. The offspring produced by each pairing are not, however, attended to by the male equally. Usually, the brood produced by the female with which the male first pairs is given the most attention, while feeding and defending of young at the other nests is carried out only when time and resources permit (2) (3). The feeding of the chicks is, however, frequently assisted by another adult, often a non-breeding bird, in a behaviour termed cooperative breeding (2). The nest, which is constructed by the female bobolink, consists of interwoven coarse grass and weed stems lined with finer grasses, placed at the bottom of a slight depression at the base of a clump of grass (2) (3). A clutch of three to seven eggs is laid, which is incubated for around 11 to 13 days. The adult and juvenile bobolinks leave the breeding grounds in late July to mid August, at which point the plumage is moulted and the birds form mixed-sex, gregarious groups that fly south to the wintering grounds (2).
During the breeding season the bobolink mainly feeds on seeds, as well as a variety of larval and adult insects and arachnids. While migrating and while at the South American wintering grounds, this species consumes wild and domesticated rice, oats, other small grains, seeds and occasional insects (2).