SCOTT SHALAWAY It's about time for birds to molt or migrate
For a reliable signal that summer is giving way to fall, watch your finch feeders. All summer long, male goldfinches have been dressed in brilliant yellow, white and jet black feathers. Soon, however, they will begin to lose their luster. Goldfinches undergo a dramatic transformation in late summer, turning from colorful feathered jewels into inconspicuous "little brown birds." Not until late April or May will these old friends again brighten our lives with their vibrant breeding colors.
The feather replacement process is called "molt." Next to nesting, it's the most important thing birds do. Feathers are critical for survival. They are essential for flight, and they streamline, protect and insulate the body.
Molt is simply the process of replacing worn feathers. Feathers are made of keratin, a tough material similar to human fingernails. But feathers wear out. The constant beating feathers take from the elements exacts a steady toll. Birds molt to counter this relentless wear. Many birds molt just once each year, after the breeding season but before migration. Replacing feathers, which make up 4 percent to 15 percent of a bird's body weight, requires a lot of energy. Timing is critical. Most birds simply can't consume enough calories to molt and breed (or migrate) at the same time.
Wing and tail feathers are usually replaced during the late summer molt. These feathers are lost and replaced a pair or two at a time, one from each side. This insures that the wings and tail remain balanced so the bird can still fly.
Some birds have a finely tuned molt pattern that occurs while they nest. But this requires, among other things, a very attentive mate. Female ospreys, for example, molt on the nest. The male brings her food while she incubates the eggs and broods the young. By the time the young ospreys leave the nest, Mom has a new set of feathers. The male, on the other hand, follows the more conventional pattern and molts after nesting.
Many water birds exhibit an entirely different strategy to replace their feathers. Ducks, geese, swans, loon, grebes, and many rails lose all their flight feathers (wing and tail) at once. This renders them flightless for four to 10 weeks, depending on the species. Water birds survive during this flightless period by living on a pond or lake that provides open water for feeding and nearby dense vegetation for escape cover.
Many birds supplement the late summer molt with a spring molt of just body feathers. This enables them to assume their bright breeding colors without the energetic stress of a complete body molt. This is the pattern goldfinches and many other songbirds follow.
But not all birds molt twice a year. Some (geese and swans, for example) molt just once a year, others (ptarmigans) three times each year, while still others (eagles and vultures) may require several years to completely replace a set of feathers. The only general rule that applies to molt is that it is a wonderfully flexible form of growth that adapts well to almost any environmental circumstance.
Changing day length, nature's most reliable environmental cue, triggers internal hormonal responses that stimulate molt. Because breeding and migration are also tied to photoperiod, the precise synchronization of all three phenomena is one of nature's more amazing achievements.
Hummingbird reminder: It's that time of year -- disregard advice to take nectar feeders down on Labor Day. Many folks fear feeders tempt hummers to delay migration until they're trapped by cold weather. But that's simply not true.
A hummingbird's instinct to migrate is too strong to be swayed by the mere promise of food. When it's time to go, they know. Hummingbirds migrate in response to shorter days, not food. Shorter days warn hummers that foul weather lies ahead.
When, then, should we take nectar feeders down? After a week or so passes without seeing any hummers. For me, that's usually mid-October.
And if you'd like a chance to attract some wayward rufous hummingbirds wandering way off course, keep nectar feeders filled throughout the fall and winter. It's a long shot, but they are seen more frequently each year.