There is a rare goose wintering with Canada and Cackling Geese at the Nestucca NWR in Tillamook Co. this season. It was discovered by an alert refuge volunteer on 9 November and has since been observed by (probably) 100’s of bird-watchers. The goose is an Asian stray called a Tundra Bean Goose (Anser serrirostris). It is the fifth occurrence of this species in North America away from Alaska, if you believe the American Ornithologists’ Union (AOU) and Dutch taxonomists…
There are many taxonomists who lump the Tundra Bean Goose with the very closely related Taiga Bean Goose (A. fabalis), in fact, the AOU considered them conspecific until 2007 when they made the split based primarily on work done by Dutch researchers. Using established differences in plumage, bill measurements, vocalizations and behavior, birds could be sorted with high reliability to one or the other of the two forms.
When these forms were banded and followed to their breeding grounds, it was found that they positively assorted to different breeding locations east and west of the Ural Mountains. The two types were recognizable forms and were reproductively isolated, which is pretty good evidence that they are different species (Sangster and Oreel 1996). But the Dutch research did not include any DNA work.
That work has since been done, but not by the Dutch. Ruokonen, et al. (2008) sampled mtDNA from multiple Bean Goose forms and Pink-footed Geese on their breeding grounds. Their data supports the distinction between Taiga and Tundra Bean Geese, but their interpretation of the distinction is that the differences do not rise to the level of species and conclude that the two types should be demoted to (or remain) subspecies within a single species complex.
On the other hand, they do recommend the elevation of Middendoff’s Bean Goose, which is currently considered a subspecies of Taiga Bean Goose, to full species status.
Does this mean that the AOU will be lumping Bean Geese sometime soon? I don’t know, but I have my doubts. The two forms are clearly on separate evolutionary trajectories, show reliably recognizable difference at the phenotypic and mtDNA levels and are reproductively isolated. Defining species solely based on degree of mtDNA differentiation is controversial.
Washington State has a record for Taiga Bean Goose from 2002, so there are some birders who might be sweating a lumping scenario relative life-list countability. Then again, it may be determined that the Washington bird was a Middendorf’s form (odds are good that it was), in which case the AOU giveth, the AOU taketh away and then they giveth, again…
Banks, R.C., R.T. Cheeser, C. Cicero, J.L. Dunn, A. W. Kratter, I.J. Lovette, P.C. Rassussen, J.V. Remsen, J.D. Rising and D.F. Stotz. 2007. Forty-eighth supplement to the American Onithologists’ Union Check-list of North American Birds. Auk 124(3):1109-1115.
Howell, S.N.G., I. Lewington, and W. Russell. 2014. Rare Birds of North America. Princeton University Press, Princeton, NJ.
Madge, S and H. Burn. 1988. Waterfowl: an identification guide to ducks, geese and swans of the World. Houghton-Mifflin, Boston, MA.