Greater Scaup

Not sure if this is a Lesser on the left and a Greater on the right, or just two Lessers or even two Greaters. If the one on the right is indeed a greater, that would be a lifer for me.

UPDATE: I'm calling the right-hand one a Greater Scaup and am leaning towards Greater on the left-hand bird as well. That's a new lifer for me.

Taken at Rocky Mountain Arsenal National Wildlife Refuge in Commerce City, Colorado on April 2, 2011.