An introduction to the complexities of molt
If you hang around the bird-watching hobby long enough there are a number of themes which you will find unavoidable. As much as you want to just sit there with your coffee and watch those feathered beauties outside your kitchen window, you inevitably get sucked into topical areas such as vocalizations, courtship behavior, migration, and taxonomy.
One I personally tried to avoid for years was molt. To the uninitiated, it seemed so confusing, so willy-nilly, so nonsensical that I figured, 'why bother.' But over and over again I kept running into people making references to molt patterns when identifying shorebirds or gulls or flycatchers. These weren't slouches either. These were heavy hitters with names like Kaufman and Sibley and Howell. No, they were obviously on to something and I needed to figure it out.
The only group of animals in the world with feathers is birds. Strong but lightweight, these complex structures serve to insulate, protect, and cover birds' bodies, among other functions. For those species that fly, well, feathers are the means by which that wonderful adaptation occurs.
As tough as feathers may be they are not permanent and over time they wear. Daily exposure to environmental conditions like sunlight, abrasion, parasites, etc., gives them a dull appearance and eventually lessens the ability of feathers to function. To maintain feather efficiencies, every species of bird replaces feathers in a process known as molt.
That's about where the simple part ends though. There is any number of variations used to accomplish this feather replacement process among bird species.
It's about here a person starts to ask the question, 'How is this going to help me understand the birds in my yard better?' For one thing, understanding molt can help us determine the age of certain birds, a critical component to some identification problems. Separating some closely related species is also enhanced by knowledge of molt patterns. Moreover, simply recognizing a worn feather or a new one on a familiar bird means we are reaching a deeper level of observation, a worthy endeavor on its own.
With that, let's wade a little deeper and start with a couple of terms. "Basic" plumage is one all birds have during some time of year. For us in the northern latitudes it's highly simplistic, but we could say basic plumage is roughly equivalent to "winter" plumage. This is a plumage achieved by the prebasic molt, usually after the nesting season.
"Alternate" plumage is the one typically associated with the nesting season and usually not held as long as basic plumage. Again we could crudely simplify this term and call it "breeding" plumage. This is a condition achieved by the prealternate molt which usually takes place in late winter and doesn't typically involve all feathers.
It's actually quite a bit more complex than this but simply understanding basic and alternate plumages is a nice start.
In terms of molt strategies, there are quite a few variations. All birds replace feathers at least once a year, some twice, rarely three times, and even more rarely, four times.
Not all the feathers are replaced at once however. Flight feathers (wings and tail) are usually replaced one at a time symmetrically with the other wing. Body (or contour) feathers are typically replaced in waves from head to tail - again symmetrically, to maintain function.
The entire concept of molt can be daunting for the average person. For those willing to tackle it, I suggest simply reading some source material followed by some careful observations. This way we might find that, while it currently displays fairly bold yellow and black feathers, the wings of American goldfinches have mostly lost the crisp white edging. Why? The wing feathers were molted last fall and have been wearing ever since.
Molt patterns have been studied for years and years and we still don't have a complete handle on it all. You would think the molt of a species as familiar as mallard (Anas platyrynchos) would be well in hand. It's not. Still, the more we learn, the deeper our understanding of these complex creatures becomes and the better we are at making informed decisions.
Corliss is a West Fargo resident, avid birder, and ND Game and Fish volunteer instructor. He serves as a corporate pilot for Forum Communications. firstname.lastname@example.org.