Montana Field Guide

The Bobolink is approximately 18 centimeters long with a stout, relatively short, pointed bill and sharply pointed tail feathers. The breeding male is black below, with a buff to whitish hind-neck, white scapulars, and white rump; early in spring the male has pale feather edgings. The breeding female is buffy with dark streaks on the back, rump, sides, and head. The juvenile resembles the breeding female but lacks streaks below. Fall adults and immatures resemble breeding female but are darker above and richer buff below (NGS 1983). Boboklinks are strongly sexually and seasonally dimorphic with respect to body mass. Mean body weights for breeding females, 29.1 grams; breeding males, 33.9 grams; migrating females, 39.9 grams; migrating males, 51 graams (Martin and Gavin 1995).

In the Bozeman area, normal migration periods are May 20 to June 5 and August 15 to September 1.

Nests built in tall grass and mixed-grass prairies. Prefers "old" hay fields with high grass-to-legume ratios.

During the breeding season, diet consists of weed seeds and a large variety of larvae and insects. During the winter, diet consists of wild and domesticated rice, oats, other small grains, corn, tassels, weed seeds, and occasional insects.

Single brooded species with five to six eggs per brood. Incubation period 10-13 days. Young able to fly after ten to fourteen days.