Determining the ages of songbirds in the field generally requires close observations, careful study, and some experience. But in a few species in spring the task can be relatively simple, and these birds provide a good starting point for understanding age variation in other songbirds. The key lies in the difference in wing moult patterns between first-year birds and older birds. The difference is really striking on birds with black wing feathers.
The crucial molting difference occurred about eight months ago, at the end of last summer, and becomes more noticeable in the spring. By late summer, adults of most species undergo a complete moult back to their winter plumage. Moulting involves all their feathers: body, wings and tail. At the same time, first-year birds only a few weeks or months old also molt into winter plumage, but their molt usually only involves the body feathers. The birds replace most of the juvenile plumage that was growing in the nest, but they retain juvenile feathers on the wings and tail.
Juvenile feathers tend to be duller and slightly weaker than those of adults, and they are also a month or more older. By the time the birds return the following spring, the flight feathers of first-year birds are relatively brownish, faded and worn, while the feathers of adults, which are stronger and blacker and have grown a month or more later , are still clean. black.
Additionally, just before spring migration, many species replace the tertials, their innermost flight feathers, at the apex of the folded wing. In first-year birds, molting creates a strong contrast between the new blackish tertials (adult-like) and the faded brownish secondary juvenile feathers. In adults, the new black tertials barely contrast with the black secondaries.
This clue to a bird’s age is particularly evident on a few common species – Scarlet and Western Tanager, Rose-breasted Grosbeak and Black-headed Grosbeak – but once learned, it can also be observed on many other species .
This article from David Sibley’s ID Toolkit appeared in the March/April 2017 issue of BirdWatching.
See photos of the Black-headed Grosbeak.
See photos of the Rose-breasted Grosbeak.
See photos of the Scarlet Tanager.
See photos of the Western Tanager.
David Sibley: How reflected light gives birds their brightest plumage.