The bird previously posted here as a presumed Yellow-billed Pintail x Marbled Teal hybrid has now been moved back to the Yellow-billed Teal x Marbled Teal page. Further input on this bird's ID suggest that this is the more likely identification. Apologies for the confusion.
Yellow-billed Pintail Anas georgica
Yellow-billed Teal Anas flavirostris
Marbled Teal Marmaronetta angustirostris