The Northern Harrier is distinctive from a long distance away: a slim, long-tailed hawk gliding low over a marsh or grassland, holding its wings in a V-shape and sporting a white patch at the base of its tail. Up close it has an owlish face that helps it hear mice and voles beneath the vegetation. Each gray-and-white male may mate with several females, which are larger and brown. These unusual raptors have a broad distribution across North America and Eurasia. Photographed in the Sacramento National Wildlife Refuge and Yolo Wildlife Basin in California.

Links:
All About Birds - Cornell Lab
https://www.allaboutbirds.org/guide/Northern_Harrier/id

Audubon
https://www.audubon.org/field-guide/bird/northern-harrier