Determining the age of songbirds in the field generally requires close views, careful study, and some experience. But in a few species in spring, the task can be relatively straightforward, and these birds provide a good starting point for understanding age variation in other songbirds. The key is a difference in wing-molt patterns between first-year and older birds. The difference really stands out on birds with black wing feathers.
The crucial molt difference happened about eight months ago, at the end of the last summer, and becomes more visible in the spring. In late summer, adults of most species undergo a complete molt to winter plumage. The molt involves all of their feathers — body, wings, and tail. At the same time, first-year birds just a few weeks or months old also molt into winter plumage, but their molt typically involves only the body feathers. The birds replace most of the juvenal plumage that was grown in the nest, but they retain juvenal feathers on the wings and tail.