Understanding Molt for Better Bird ID

While banding, one of the most important pieces of information collected about a bird is its age. For songbirds, banders are generally determining whether a bird is a younger bird or an older bird, typically by looking for differences in molt (after the breeding season, young birds and adult birds molt differently, generally allowing us to distinguish ages until the next breeding season).

Some birds have cryptic feathers and molt patterns making aging difficult to impossible. And then others (like thrushes) have some easy age clues. A common trait among juvenile thrushes is spotted breasts and pale shaft streaks in the greater coverts.

While the spots will disappear after summer (think about young American Robins and the lack of spots come fall), the shaft streaks will remain until they molt the following year. For banders, these streaks stand out right away and generally tell us that the bird is young (a hatching year in the summer/fall or a second year in the spring/summer).
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If the streaks are bold enough, you can even see or photograph them in the field! This lets you know you’re looking at a younger thrush.