Early August is when birds get noticeably quiet.
Most songbirds have finished nesting and have ceased singing. Now, it’s time for another major period in their lives, their annual post-breeding molt, in which old and tattered feathers are replaced with new ones. Healthy feathers, of course, are vital — not only for flying, but also for keeping a bird cool or warm as well as dry.
Feathers, though, wear out from constant flying, sunlight, abrasion, swimming, nesting and other causes, and must be replaced.
It makes sense that most birds molt in late summer and early fall. For most of them, the hectic tasks of raising babies are over, and ample food is still available to provide energy for the physically demanding molting process. For migratory birds, it also means that they will have a new set of feathers to make their long, arduous fall journeys.
(Tip: Suet is an excellent energy source for birds that are both molting and getting ready for fall migration.)
Birds lose and replace every one of their feathers, beginning at the head and working toward the tail. For ruby-throated hummingbirds, that’s about 940 feathers; for a song sparrow, about 2,200 feathers.
Molting occurs gradually, so you won’t see a featherless adult bird. You may, however, occasionally see a “bald-headed” cardinal or blue jay that has temporarily lost its head feathers, although molting may not be the only cause.
Not surprisingly, a molting bird is less agile than usual, which makes it more vulnerable to predators. So, it pays for the bird to be more reclusive and quiet at this time and not call attention to itself.
Not all birds are equal when it comes to molting. Nearly all songbirds will undergo a complete post-breeding molt, which, for many species, will be the only molt of the year. However, several other species — buntings, tanagers, warblers, goldfinches — also undergo a partial “pre-nuptial” molt in spring to don their brilliant breeding plumage.
A few species, such as marsh wrens and bobolinks, have two complete molts during the year. Some larger birds, such as eagles, require two full years to complete their molts.
In the sky: The moon will be first quarter Sunday, said David Dundee, Tellus Science Museum astronomer. Venus rises out of the east about an hour before dawn. Mars is in the west at dusk and will appear near the moon Saturday night. Saturn is low in the west at dusk and sets around 9 p.m.
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