This is at the end of the range of my little Coolpix setup, but still is diagnostic for Hudsonian in flight. The black underwing with white stripe is shown only by Hudsonian, the similar Black-tailed (that WOULD have caused a stir!) has a white underwing. Jeff Wilson, who (as usual) found the bird, got a flight shot that will make your jaw drop. I'll take what I can get though.