I just read Yong's piece on Dusky Canada Geese. We just published The Crossley ID Guide: Waterfowl (with Paul Baicich and Jessie Barry). We cover the Cackling and Canada Goose in some detail. They are a very complex group and there is still so much to learn about them. I had the good fortune to spend some time travelling the continent looking at them, often being confused, recognizing the futility of trying to identify some subspecies and finding a few things that were definitely a surprise. For instance, there is no known breeding record of Lesser Canada Goose for Canada, contrary to what all the literature says (yes, we authors do sometimes copy others without knowing). I assume the Lesser Canada Goose, as we know it, will turn out to be mass hallucination, and the dark 'small' Canada Geese best known from the Anchorage area will turn out to be the Canadas that have a slightly different DNA to the bigger ones. These Alaskan Lesser Canadas in turn form what some consider a cline with Dusky and Vancouver Island birds - getting smaller to the north as other geese do. Putting nature in a nice square box to tick is not always that simple . thankfully!