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Late summer is the time of year when many birds replace their feathers in a process called molting. Old feathers, most of which have been worn for about a year, fall off and new feathers grow in their place. Seagulls, for example, only shed their wing feathers once a year and we usually don’t notice any change in their appearance. The color and pattern of their wings remains the same throughout the year. After a year of constant wear and exposure, it’s amazing that the nibs still work, let alone maintain essentially the same appearance.
If you’re at the beach this time of year, you’re likely to find feathers on the sand. Virtually all of these feathers will be old feathers, “used” by the birds for up to 12 months, then discarded during the normal molting process. Among them you may find large wing feathers left by seagulls. It is illegal to keep these feathers, but you can pick them up and examine them.
When you find a nib, examine it closely and look for signs of wear. Pay particular attention to the most worn parts. If it is a typically worn nib, as shown here, most of the light parts will be disintegrated, while the darker parts will be a little frayed but more or less intact. Indeed, the dark pigment, melanin, strengthens the feather, making it more resistant to the elements. Gull feathers often end in notches at the tip or sides where the lighter colors have worn off, and not the dark parts of the feather. This is why birds with heavily worn plumage generally appear darker, as the lighter edges and markings have simply disappeared, and all we see are the darker parts that remain.
This also explains why so many birds have dark wingtips. The tips of the longest feathers are subject to the greatest wear, but they are also extremely important for flight and cannot deteriorate or change shape. An infusion of melanin at the tips is a kind of protective treatment birds have developed to keep their feathers functional for an entire year.
This article from David Sibley’s ID Toolkit appeared in the July/August 2018 issue of BirdWatching.
David Sibley: How birds can change color without moulting
The enigma of the moult: should we say “juvenile” or “juvenal”?