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Scientific Name: Dolichonyx oryzivorus
Common Name:

(Information for this species page was gathered in part by Ms. Emily Bolewitz for Biology 220M at Penn State New Kensington in Spring 2013)

The bobolink (Dolichonyx oryzivorous) is a small (seven inches long and an ounce in weight) blackbird formerly found in great numbers across the northern United States and southern Canada. Loss of natural grassland habitats in its northern breeding range along with the loss of both grassland and marshland habitats in its southern, over-wintering range has seriously reduced the population density of this species.

male bobolink - Image credit: Steve Maslowski, US Fish and Wildlife Service Digital LibraryThe bobolink has two plumage and coloration patterns. The first, seen in breeding males, is the extremely distinctive solid black underside coloration with a pattern of white above and a straw colored patch on the nape of his neck (Image: Steve Maslowski, retrieved from US Fish and Wildlife Service Digital Library). The breeding male bobolink is the only song bird that is all black below. The females (and the non-breeding males) are a rich yellow-brown color with dark brown stripes on their heads and backs. They have short, conical, “sparrow-like” bills that are darker (nearly black) in the male.

Bobolinks are omnivorous and will eat a mix of available insect and plant foods. In the summer they consume slightly more insects than plant foods, while in the winter they eat abundant plant seeds. They have a common name of the “rice bird” because of the tendency of large, migrating flocks of bobolinks to descend on rice fields and consume great quantities of the grain. Nestlings are fed caterpillars almost exclusively by the parental birds.

Migration and Territory
The bobolink is a long distance migrator and typically covers at least ten thousand miles in its yearly round trip flight. Summer ranges are natural grasslands and/or pastures and hayfields of the northern United States and southern Canada, and winter ranges are grasslands and wetlands of South America (including Chile, Bolivia, Argentina, and Brazil). Males arrive first at their northern breeding ranges in mid to late April and vigorously compete with each other for territory. The territories are quite varied in size (average is about an acre) but an optimal territory will include both a variety of perches on which the male can display himself and sing and abundant herbaceous plants which will be the source of caterpillars for the nestlings. Males attempt to have as large a territory as possible so that they might possibly support and mate with more than one female. This allows the male to pass along his genes to a larger number of offspring. Females, however, tend to preferentially mate with males who have smaller territories that will support just one female. This female preferred monogamy insures the full energy and attention of the male on the nest of her young.

Mating and Reproduction
Males go through an energetically demanding set of displays of both singing and flying in order to attract a female. The duration and energy of these displays are directly related to the male’s reproductive success. Males have two versions of their distinctive song. One is designed to attract females and the other is designed to aggressively repel intruding males. Once a female has selected a male, she builds her shallow, ground nest of loosely woven grasses and weeds typically in a slight depression among the dense ground vegetation. Nests are located away from trees or shrubs possibly to prevent potential nest predators from obtaining an easy view of its location. Everything about the nest and its location is designed to make it as inconspicuous as possible. Predation, though, results in a very high rate of nest failures.

Bobolink eggs are also highly camouflaged. They are a light brown with dark brown blotches and and tend to fade into the background of the soil and litter system very well. Females typically only lay one clutch of four to six eggs in a breeding season. They can, however, in the event of a nest failure lay a second clutch of eggs. The female incubates the eggs for twelve days. Nestlings will fledge after ten more days. Both parents gather caterpillars to feed the voracious nestlings, and the full attention of the monogamous male significantly increases the chances for nestling survival.

Ground based nests are very vulnerable to predators. Many of the “usual suspects” of egg and nestling predators affect bobolink nests (including skunks, raccoons, foxes, and snakes). A surprising bobolink nestling predator is the white-tailed deer. It is not known how many nestlings are eaten by deer each year, but up to 70% of bobolink eggs and nestlings are lost to predation each breeding season.

The brown-headed cow bird is a common nest parasite for bobolinks. Not only do the female cowbirds lay their eggs in the bobolink nests, but they may also actively destroy nests in order to stimulate new nest building (and, thus, new opportunities for nest parasitism).

Bobolinks require large, open, grassland spaces in order to breed and nest. They avoid forest edges and also road edges. Habitat fragmentation may be a more significant force causing their population declines than pure habitat loss.

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