This is an interesting combination. The male on the left is a Greater Scaup, but the female is a Lesser Scaup. The shape of the head is the primary marker. There were several individuals of both species in the water so this is likely just a coincidental meeting and not a “rendezvous”. Both species are in the process of migrating to their summer breeding grounds. Greater Scaup are headed for Alaska and across the very northern portion of Canada. Lesser Scaup breeding grounds extend from Montana, Wyoming and Idaho through the western Canadian provinces into Alaska.
Birds in My Viewfinder 
Finally photographs where you can clearly see the difference by the shape of the head.
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