Using Molt to Age Birds

Adult Common Raven Corvus corax

At this time of year in North America, and likely in most of the temperate areas of the northern hemisphere if you get a chance to see the primary feathers of a bird, you can often tell if it is a bird born that year, i.e. a juvenile, or a bird born at least a year ago. If it is a bird born at least a year ago it will be undergoing the replacement of it's primary and secondary wing feathers and its tail feathers. Collectively these are called the "flight" feathers.
In a bird of the year all of the flight feathers are brand new, and won't be replaced until more than a year from their birth, i.e. the first complete molt after the next breeding season.

Note that every flight feather is in perfect condition in this Juvenile Osprey Pandion haliaetus. It hatched from a nest at the Chambers Bay Golf Course this year.

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