If you see a small hawk with a white rump hunting in the marsh grasses, it’s a Northern Harrier.
Cornell:
“A long-winged, long-tailed hawk of open grassland and marshes, the Northern Harrier forages by flying slowly low above the ground looking for small rodents. It is one of the few raptors in which the sexes look quite different: the male is white below with a light gray back and hood, the female is mottled in browns.”