This species has increased markedly in the San Francisco Bay region at the expense of the formerly more common Lesser Scaup. Greater Scaup is the only circumpolar member of the Aythyini tribe. This is an adult male showing greenish face and rounded head. Two subspecies are usually recognized, this being the North American "A. m. nearctica." They differ from Eurasian birds in that North American males are more coarsely marked above. Some sources (e.g. IOC) attribute "nearctica" to East Asia apparently based on a misinterpretation of Banks (Wilson Bull., 98(3), 1986, pp. 433-444.)
