The Eastern Marsh Harrier is a fairly large (M 48 cm; F 58 cm) raptor which is quite variable in plumage. Males are blackish above with white mottling, a black and white streaked head (sometimes all black), darker on the face, and whitish underparts streaked with black; the tail is gray. In flight, the wings are mostly gray above, with black outer primaries, and the rump bears a white patch. The larger female is brown overall, lighter on the head and belly, with heavy streaking. In both sexes the bill is gray and the iris and legs are yellow.
The Eastern Marsh Harrier is a bird of coastal marshes, swamps, lake edges, large reed beds and other open areas such as rice fields and grasslands. In migration it is seen over mountains. It is an opportunistic feeder, taking a wide variety of prey including rodents, small birds, disabled aquatic birds, nestlings and eggs. It hunts by gliding low over open habitats, attempting to surprise prey.
In Taiwan the Eastern Marsh Harrier is an uncommon winter resident.