Recently while walking in Ash Creek Wildlife Area (Lassen County CA) a “hawk” was perched on a directional sign. I moved toward the bird and it did not fly away, so I continued to approach. Surprisingly I got within about ten feet before the bird flew off. Usually raptors do not let me get that close.
When the bird flew, Leonard and I saw its distinctive white rump patch and knew the “hawk” was a northern harrier (Circus hudsonius). Male northern harriers are grey and black in color while females (and immatures) are brown. This was a female and/or immature. When I looked at the photographs, the dark brown eye further identified the harrier as an immature female since adults have yellow eyes, immature male eyes are greenish yellow and immature females have brown eyes.
Northern harriers are unlike many other raptors in that they rely on both vision AND hearing to locate prey. The face of a northern harrier resembles the disk-shaped face of an owl and functions in similar manner to an owl, although harriers are not related to owls. Stiff feathers in a parabola arrangement direct sound to the ears and aid in hearing. This adaptation is probably helpful to the northern harrier as it flies over tall, thick grass searching for its main prey, small rodents. In the photograph the stiff facial hairs are visible, although they have not yet matured into a smooth disk.
Marsh hawk was formerly the common name of C hudsonius. I tend to still call this bird a marsh hawk since that was the name I first learned. Circus cyaneus is a synonym.
More information about marsh hawks can be found in my earlier post: Northern Harrier on 04-05-12.