Adult Female (Olive drab to orange bill): Left
Adult Male (Bright Yellow Bill): Right
Distinguished from the American Black Duck (A. rubripes) by black spot on gape.
This species is closely related to the Mallard Duck (A. platyrhynchos)
It is in danger of being displaced to introduced Mallards,
primarily due to hybridization.
Aransas National Wildlife Refuge
Port Aransas, Texas