The Montagu's harrier is a small bird of prey, measuring 40 to 50 cm in length and weighing 220 to 300 grams. The female harrier is larger than the male and weighs 250 to 450 grams. The wingspan is 100 to 120 cm. The males and females have distinct plumage. The males have pale grey plumage. They have black primaries and black bands across secondaries feathers. In adult female harrier, the plumage is mostly pale yellow-brown on underparts and the belly has longitudinal stripes. The wing coverts are spotted. The male makes a display call of “kek..kek..kek" sound.
