What to look for as birds molt their worn-out feathers

molt
Here are two views of the sixth primary of a Ring-billed Gull. It’s freshly grown in the fall (upper) and very worn in the late summer of the following year (lower). Art by David Sibley

Late summer is the time of year when many birds replace their feathers in a process called molt. Old feathers, most of which have been worn for about a year, fall out, and new feathers grow in their place. Gulls, for example, molt their wing feathers only once a year, and we generally don’t notice any change in their appearance. The color and pattern of their wings remain the same all year. After a year of constant wear and exposure, it’s amazing that feathers still function, let alone retain essentially the same appearance.

If you are at the beach at this time of year, you will probably find feathers on the sand. Virtually all of these will be old feathers, “used” by the birds for up to 12 months and then dropped in the normal process of molt. Among them you might find large wing feathers dropped by gulls. It’s illegal to keep these feathers, but you can pick them up and examine them.

When you find a feather, take a close look at it, checking for signs of wear. Pay special attention to which parts are more worn. If it’s a typical worn feather, as shown here, most of the light-colored parts will have disintegrated, while the darker parts will be a bit frayed but more or less intact. This is because the dark pigment, melanin, strengthens the feather, making it more resistant to the elements. Gull feathers often end up with notches at the tip or along the sides, where lighter colors have worn away, and the dark parts of the feather have not. This is why birds in very worn plumage generally look darker, because the lighter edges and markings have simply worn away, and all we see is the darker parts that remain.

This also explains why so many birds have dark wingtips. The tips of the longest feathers are subjected to the most wear and tear, but they’re also extremely important for flight and cannot be allowed to deteriorate or change shape. An infusion of melanin at the tips is a sort of protective treatment that birds have evolved to let their feathers remain functional for an entire year.

 

This article from David Sibley’s “ID Toolkit” column appeared in the July/August 2018 issue of BirdWatching.

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David Sibley

David Sibley

David Sibley writes the column “ID Toolkit” in every issue of BirdWatching. He published the Sibley Guide to Birds in 2000, the Sibley Guide to Bird Life and Behavior in 2001, and Sibley’s Birding Basics in 2002. He is also the author of the Sibley Guide to Trees (2009), the Sibley Guide to Birds-Second Edition (2014), and guides to birds of eastern and western North America (2016). He is the recipient of the American Birding Association’s Roger Tory Peterson Award for lifetime achievement in promoting the cause of birding and a recognition award from the National Wildlife Refuge System for his support of bird conservation.

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