|Juvenile Western bluebirds in molt look a bit bedraggled. Photo by Ken Tomb|
Have you noticed that birds seem to keep a low profile this time of year?
“I’ve had people ask me why they don’t see mockingbirds around in August,” said Sylvia Gallagher, chairwoman of bird information for Sea and Sage Audubon, Orange County’s local chapter. “Well, they’re definitely here, but they’re not singing and they’re molting.”
Molting is a systematic process of replacing feathers. Birds tend to become secretive during this time, vocalizing infrequently and hiding in the vegetation. That’s because they’re more vulnerable to predators during molt, especially when growing new flight feathers. It may take weeks or months for them to complete the molting cycle.
Feathers are important to a bird’s survival, so they spend a great deal of time taking care of them. After bathing, they use their bills to preen. Each feather is coated with oil from a gland at the base of their tails to prevent it from becoming dry and brittle. Feathers need to be in good shape for flight maneuverability. They also insulate birds from the cold and make them virtually waterproof.
“Every bird has a complete molt once a year,” Gallagher said. “Most birds molt in late summer and early fall, but the way birds molt differs among species. Some have a partial molt, then migrate. But they’re not normally in a full molt when flying long distances.”
Because molting requires a lot of energy, it usually kicks in after breeding. Many undergo a complete molt on or near their breeding grounds, which allows them to migrate south with a new set of feathers.
Some songbirds, such as the Western kingbird, will migrate partially south to the monsoon areas of southwest Arizona and New Mexico to molt. There the rain brings an abundance of insects for them to feed on. After molting their flight feathers, they continue migrating south to their wintering grounds.
Molting patterns can even differ among closely related species, such as goldfinches, she said. American goldfinches molt twice a year, once in early spring when males sport their bright yellow breeding feathers and again in the fall when they exchange them for a more drab winter garb. Lesser goldfinches molt only in the fall.
Waterfowl, including ducks, loons and grebes, lose all their feathers at once, rendering them flightless for about a month. During this time, male ducks molt into a brown eclipse plumage, which resembles the female coloring. Once the male’s wing feathers have regrown and they are able to fly, drakes will begin to grow the bright colors on their heads and body.