17 November 2008

Cackling vs. Canada Geese

In March I found at least two of what I considered to be Cackling Geese (photo above), a recently-designated species that used to be considered part of Canada Geese. I submitted a report to the Bird Records Committee for Utah, because Cackling Goose is on the review list for the state. Although identification of this species can be difficult with certain subspecies, it is easier with others. The birds I saw were not the easy-to-identify subspecies. I beleive they were Taverner's Cackling Geese, Branta hutchinsii taverni. The record was just voted on for the second time, and was rejected. This surprised me, as I felt fairly confident in my identification. So, I've spent a lot of time reviewing photos, identification articles, and other documents on the identification of these species (such as this, this, and this), to try to determine where my fault lies. Either I misidentified this species, in which case I should remove it from my list, or I wrote a report that was insufficient to convince the committee that I saw what I did, in which case the bird would remain on my list.

After much careful review, I am still convinced that I saw at least two Cackling Geese on that day. The trouble with the review of the record lies in that the smallest Canada Goose, the Lesser Canada Goose, overlaps in many traits with the largest Cackling Geese, such as Richardson's and Taverner's Cackling Geese. I did not make the case well enough that the Lesser Canada Goose could be excluded, although I do believe that from my photos and the features I observed it can. The comments of the committee are particularly interesting in this respect. For example, "I still think most of the features point to a Taverner's Goose," "I don't feel at all confident identifying the white-cheecked geese that aren't at the extremes of size/shape," "the written description fits Cackling Goose," "Looks like we share the same doubts about identifying the mid-range Canada/Cacklers from each other," and "I almost want to rescue myself from this vote because I am still struggling with the definitive identification of the various subspecies of the Canada/Cackling Goose complex . . . could possibly be the taverni or hutchinsii subspecies."

Of course, these comments are obviously taken out of context and are incomplete, but I think they convey the level of uncertainty held even by experts in distinguishing this pair of species. In summary, I don't blame the committee at all for not accepting this record. These are tough species to tell apart, and my record did not do an adequate job of describing and documenting the traits that showed that these were Cackling Geese. The committee did the right thing in not accepting a record of which they were not certain. However, I remain convinced that these were in fact Cackling Geese, and not Lesser Canada Geese. In fact, I'll go a step further and say that as our identification and knowledge of these two species improves, I think we'll find that Cackling Geese are more common in Utah in winter than we currently believe. In the meantime, I'll make it a goal of mine to 1) get to know the differences among these species and subspecies even better and 2) thoroughly and convincingly document Cackling Geese if and when I encounter them in Utah in the future.

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