What specialized physical feature, similar to owls, does the Northern Harrier possess to aid in hunting?

Answer

A facial disc or ruff of feathers

Harriers possess a ruff of feathers around their face, known as a facial disc, which helps direct sound to their ears, pointing toward specialization in hunting by sound and sight close to the ground.

What specialized physical feature, similar to owls, does the Northern Harrier possess to aid in hunting?
birdraptorhawkFalconNorthern Harrier