On this picture you can see the owl-like facial disk that Northern harriers wear:
Northern harriers are found in open grass and marsh lands (historically called the “marsh hawk”), and they tend to fly low over the landscape in search of small mammals, insects and lizards which are one of their main sources of prey. They have a small facial disk, similar to owls, and it is believed they use this to use focus sound when hunting in the same way that it is said that owls do.
Males and females are sexually dimorphic, meaning in this case that they have very different adult plummages. Males are white and gray with black on the wingtips of the primary feathers, while females (and sub-adults) are dark brown overall with a cinnamon or pumpkin coloring on their underside (sub-adults tend to have more of a cinnamon coloring). One of their features that is helpful for in-flight ID is their white rump patch, seen on all of them. They also tend to hold their wings in a slight dihedral (v-shape), while gliding low over the ground.
Interesting, these birds nest on the ground.
They are fun to watch, as they glide over the landscape almost like butterflies teetering in the wind.