Everything in nature has multiple connections, so in studying bird ID, we don’t just look at the physical field marks of the bird in isolation. We have to think about habitat, behavior, total distribution, and many other factors.
The Snow Goose provides a perfect example. The challenge of identifying this species has changed in intriguing ways during recent decades. It’s not that the bird looks different today; the change is driven by a huge population increase and range expansion of white geese in general.