One of the most defining features of a bird is its plumage. But as complex and capable as feathers are, they don't last forever: They begin to break down after some time, forcing its owner to replace them. As a result, a bird’s appearance may radically change through the molting period—or just look odd and patchy. That, in turn, adds another layer of difficulty to species IDs. My advice to birders who are agonizing over these transitions: Embrace the molt. It's a fascinating behavior, just like migration and breeding, and it's one of the vital parts of a bird’s life; plus, it can add some interesting context to your next birding outing. Let's look at some of the fundamentals of identifying molts. Are molts obvious? Yes, though more so in larger species and in longer feathers on the wings and the tail. When birds are molting, you can usually spot the missing primary flight feathers by looking for a gap in the outline of the wing. The molt...