You may have noticed that in the middle of the summer, birds seem to disappear and the singing in the woodlands becomes silent. During this time, many bird watchers hang up their binoculars until fall migration. But there’s no reason for you to stop birding. The birds are still out there, they’re just keeping a very low profile. Why? Because they’re replacing their feathers.
It's called molting and molting patterns can vary by species, by individual and from year to year. Molts can be either complete, in which the bird replaces every one of its feathers over the same molt period; or partial, in which the bird replaces only some of its feathers - flight feathers or body feathers. Molting keeps birds in top flying condition by replacing feathers that have become worn or damaged with completely new feathers. However, if a bird loses an entire feather, that feather will begin growing back immediately rather than waiting for the next molt.
Many groups of birds employ different molting strategies depending on their annual schedule. Most eastern songbirds, including Baltimore Oriole, Chestnut-sided Warbler and the Indigo Bunting will begin replacing their flight and body feathers shortly after their young fledge. And then migrating south after they have a new set of feathers.
Molting is energetically expensive—as is migration and breeding. So, birds make sure these three activities don't overlap. For many of our North American songbirds, that sweet spot in the calendar is July into early August. Townsend’s Warblers, for instance, go through a complete molt during this time, after they're done mating, nesting, and tending to their chicks, but before they embark on their southbound migrations. Other birds such as Gray Flycatchers fly down to their tropical grounds first to wrap up the process there. Tree Swallows, meanwhile, may begin the swap up north, pause for migration, and then complete it after arriving at their wintering destinations.
There are some songbirds in the West, however, that begin their migration south a bit before molting. Western summers can be extremely dry and desolate, so many species including the Western Kingbird and Lazuli Bunting will head off on a partial migration to the Mexican Monsoon region (southeast Arizona, New Mexico, and northwest Mexico) to molt. One of the main reasons they travel to these locations is because monsoon rains brings an abundance of insects on which to feed. After they have molted their flight feathers, they continue their migration south to their wintering grounds.
And then there is the American goldfinch. All summer, this beautiful glowing yellow male American goldfinches are hanging out at your feeder - and then one fall day there’s not a bright yellow colored songbird to be found. In fact, the goldfinches are still around and coming to feeders. They just look different—drab and dull. The female American goldfinch color changes are very subtle, but the male is much more dramatic. He transitions from blazing yellow to a much duller yellow-brown, making him look more like the female. His feathers aren’t actually changing color. Instead, the bird gradually replaces all the feathers in the molting process. If you spot the male goldfinch in the middle of molting, he’ll have patches of yellow and brown.
Bird Watching During The Summer Molt
Spotting a molting bird is just a matter of taking a minute to carefully look at the feathers. Molting warblers and thrushes in woodlands tend to be tricky to see, but grackles and other blackbirds in the open country are often easy to spot. Birds in heavy molt tend to be a little scruffy overall, so look for contrast between new and old feathers, and gaps in their wings where old feathers have been dropped and new ones have just started to grow.
After learning the basics here, the next step is to get familiar with the habits, schedules, and variations of specific groups of birds. The Peterson Reference Guide to Molt in North American Birds is a great all-encompassing resource and field guide. You can also practice at home by noting the different plumages in the birds that come to your feeder. Look for darker and fresher feathers and contrast them with the paler ones.
Once you begin to spot a molting bird, you will have an appreciation of the changes a bird goes through to survive each year. And you’ll appreciate how birds must prepare for the long journeys of their fall migration.
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