Many birds, like humans, use the summer months to recharge their batteries. After the exhausting task of building a nest and rearing young, the fresh breeding plumage of spring slowly becomes faded and worn.
The essential role of feathers in protecting a bird, not to mention their role in flight, makes it necessary to periodically shed old ones and replace them. Therefore, after the summer’s hatchlings are out of the nest, many species undergo a molt, or a complete overhaul of their feathers.
The abundance of food this time of year makes the process less energetically risky, but molting is still a very stressful time in a bird’s annual calendar. Flight might be compromised when wing and tail feathers are being replaced and the insulating role of body feathers is similarly reduced, but it is a necessary activity if a bird is to maintain its health.
Though molting is not the easiest activity for a bird, it provides an interesting study for the curious birder.
Many species, particularly migrants like tanagers, grosbeaks, and warblers, undergo a dramatic plumage transformation once breeding is complete. Trading in the bright colors of spring, these species prepare for their long journey south by donning a much drabber plumage.
Furthermore, a detailed knowledge of molting can be a valuable tool in determining the age of a particular individual. Scientists look for contrasts in color and wear on a bird’s wing or tail, the old feathers being distinct from the new, fresher ones.
Many large birds, such as gulls and eagles, can be aged by distinct plumages that change with each subsequent year. Birds in the middle of their molt can often look ragged, sporting a strange combination of older feathers with new ones.
At this time of year it's not uncommon to see half-yellow American Goldfinches and Gray Catbirds missing most of a tail. Despite this awkward change, molting ensures our birds are ready for the difficulties of the upcoming fall and winter seasons.