Montagu’s harrier – Circus pygargus
is a migratory bird of prey of the harrier family. Adult males are characterized by their overall pale grey plumage contrasting with black wingtips. Compared with other harriers this species has characteristic black bands along the secondaries, both above and below the wing and rusty streaks on belly and flanks. Adult females have a broadly similar plumage to that of pallid and hen harriers. The underparts are mostly pale yellow-brown, the belly with longitudinal stripes and the wing coverts spotted. The upper parts are uniform dark brown except for the white upper tail coverts (“rump”), and the sightly paler central wing coverts.

The juvenile plumage resembles that of the female, but differs by the belly and under wing coverts which are not spotted, but uniformly red brown in colour.

A melanistic form occurs regularly in this species. In this form the male is much darker than usual, with a black head, brownish black above and grey underparts. The melanistic female is entirely chocolate brown except for grey flight feathers. Partially melanistic morphs can also be found.

The Montagu’s harrier can be confused with several species that exist within the same range. The most similar are the hen harrier and the pallid harrier. The male is easily distinguished from other species as its plumage is distinctly darker and more mottled than in the males of hen or pallid harriers. However, distinguishing females and juveniles is more difficult. Usually the Montagu’s harrier appears more slender in flight than the hen harrier with a longer tail, longer and narrower wings and more pointed “hands”. Also its flight is more elegant than the hen harrier, with more elastic, almost tern-like wingbeats. The distinction between female pallid and Montagu’s harriers is the most delicate and can only be made in good conditions as the proportions are similar. The best recognition character is the pale collar around the neck of female and juvenile pallid harriers which is not present in the Montagu’s.

It sounds like this
Recording by José Carlos Sires from xeno canto