Goodbye Northwestern Crow, hello Mexican Duck

The latest supplement to the American Ornithological Society's Checklist of North and Middle American Birds, published in The Auk: Ornithological Advances, includes several major updates to the organization of the continent's bird species, including the addition of the Mexican Duck and the removal of the Northwestern Crow. The official authority on the names and classification of the region's birds, the checklist is consulted by birdwatchers and professional scientists alike and has been published since 1886.

The Northwestern Crow has long been considered a close cousin of the more familiar and widespread American Crow, with a range limited to the Pacific Northwest. However, a recent study on the genetics of the two species prompted AOS's North American Classification Committee to conclude that the two species are actually one and the same. "People have speculated that the Northwestern Crow and the American Crow should be lumped for a long time, so this won't be a surprise to a lot of people," says the U.S. Geological Survey's Terry Chesser, chair of the committee. "Northwestern Crows were originally described based on size, being smaller than the American Crow, and behavior, but over the years the people who've looked at specimens or observed birds in the field have mostly come to the conclusion that the differences are inconsistent. Now the genomic data have indicated that this is really variation within a species, rather than two distinct species."

However, birdwatchers disappointed to lose the Northwestern Crow from their life lists can take solace in the addition of a new species to the official checklist: the Mexican Duck. "The checklist recognized Mexican Duck until 1973, when it was lumped with Mallard," says Chesser. "But the Mexican Duck is part of a whole complex of Mallard-like species, including Mottled Duck, American Black Duck, and Hawaiian Duck, and all of those are considered distinct species except for, until recently, the Mexican Duck. Now genomic data have been published on the complex and on the Mexican Duck and Mallard in particular, and they show that gene flow between them is limited, which was enough to convince the committee to vote for the split."

Additional changes introduced in this year's checklist supplement include a massive reorganization of a group of Central American hummingbirds known as the emeralds -- adding nine genera, deleting six others, and transferring seven additional species between already-recognized genera -- as well as an update to the criteria for adding introduced, non-native species to the list that raises the bar for introduced species to officially be considered established. The full checklist supplement is available at https://academic.oup.com/auk/article-lookup/doi/10.1093/auk/ukaa030.