Identification Challenge: Lesser v. Greater Scaup
Winter in Arizona is the season to search for and study the many northern-breeding ducks that overwinter in this region. At this time of year, most ducks are readily identified based on size, plumage, behavior, voice, and/or habitat. This is, however, often not the case for Lesser and Greater Scaups (Aythya affinis and A. marila) because these species resemble each other, behave similarly, rarely vocalize, and can use the same habitats and be found together. As a result, distinguishing them in the field has long posed a challenge. The two scaup species winter regularly in Arizona, but in vastly different numbers (Monson and Phillips 1981): Lesser Scaup is widespread, whereas Greater Scaup is scarce outside the lower Colorado River region. Acknowledging the scarcity of the Greater Scaup, it is listed as a Sketch Details Species, whose occurrence outside the lower Colorado River region should be documented through notes or photos. As many Arizona birders may have limited first-hand experience with Greater Scaup, learning to separate this taxon from the Lesser Scaup is essential in order to identify it correctly.