The bobolink is the only North American bird that has light feathers above and dark feathers below, coloration that helps bobolinks hide from predators in the blowing grasslands. Male upperparts are black, with a pale, yellowish tan nape and white along the sides of the upper back, lower back and rump. Underparts are all black. Female's upperparts are buffy with dark streaks; the crown is dark with a central light streak, the eyebrow is light-colored and there is a dark eye line behind the bill; underparts are pale buff, with streaks on the flanks. In fall and winter, the male resembles the female but is darker above. Song is a bubbly series of musical gurgles and whistles, often sounding like "bob-o-link," and is frequently given during stiff-winged courtship flights. Call is a sharp "pink."