I'd guess the area has a large population of Townsend's Vole. They are the
food of choice here on Whidbey for Red-tailed Hawks and Northern Harriers.
You should see all the holes and runs they create in Smith Prairie, an
area near Coupeville. They also thrive in weedy/grassy ditches leading to
collisions between vehicles and raptors.
There are lots of other things for raptors to eat on the Samish Flats
including shorebirds and waterfowl.
Steve Ellis Coupeville, Wa
sellis at coup.wednet.edu