Originally posted July 2013; updated May 2021.
In the dog days of summer, birds seem to disappear—the dawn chorus wanes and an odd silence takes hold in woodlands. Many birds look bedraggled, no longer sporting their bright breeding colors. A lot of birders hang up their binoculars until fall migration. (July and August are typically the two lowest months for eBird checklist submissions.)
But there’s no reason to stop birding. The birds are still there, they’re just keeping a low profile, because they’re replacing their feathers. Knowing what’s going on in the post-breeding lives of birds can help you keep finding species late into the summer.
Birds sing for two basic reasons: to attract a mate and to defend a territory. By July, many baby birds in North America have fledged, and even birds that have multiple nests per year have finished by early August.
Some birds may continue singing for a while to help their young learn their local song dialect. But many birds, such as American Robins and Red-winged Blackbirds, stop holding territories and start to join flocks—and territorial singing just isn’t compatible with flocking. One by one, each species drops out of the morning chorus.
Lying Low During Molt
After breeding, the molting season kicks in, heralding major changes in both the appearance and behavior of birds. Molt is the systematic replacement of feathers. All birds do it—from hummingbirds to penguins. They have to molt in order to survive, because feathers wear out from physical abrasion and bleaching from the sun. Once a year (in the late summer for temperate species) birds grow an entirely new set of feathers through a complete molt.
As birds grow new flight feathers, they are particularly vulnerable to predators. During wing molt, several of their flight feathers will be less than full length, producing gaps in their wings that render them less maneuverable and powerful in flight. To avoid attracting the attention of predators, many birds—such as sparrows, warblers, and thrushes—lie low, calling infrequently and hiding in vegetation.
Drakes Go Incognito
Brightly colored male ducks have an extra trick to avoid being conspicuous to predators during molt. Waterfowl, including loons and grebes, lose all of their primary and secondary feathers at once, rendering them flightless for about a month. To help them hide when they can’t fly, male ducks grow a special set of camouflaged feathers, called eclipse plumage. In July, you may notice all the Mallards in a local park look scruffy and mostly brown, like they’re all females. Shortly after their wing feathers have regrown and they are able to fly again, drakes will regrow their brightly colored body feathers.
Groups of birds employ different strategies to fit molt into their annual schedule. Most of eastern North America’s songbirds, including Chestnut-sided Warbler, Baltimore Oriole, and Indigo Bunting, begin replacing their flight and body feathers shortly after their young fledge. They tend to undergo this complete molt on or near their breeding grounds, migrating south after they have a new set of feathers.
Some songbirds in western North America, however, begin their migration and fly south a bit before molting. Western summers can be extremely dry and desolate. Many species—including Western Kingbird and Lazuli Bunting—head off on a partial migration to the Mexican Monsoon region (southeast Arizona, New Mexico, and northwest Mexico) to molt. The monsoon rains brings an abundance of insects on which to feed. After molting their flight feathers, these birds continue their migration farther south to their wintering grounds.
Birding During Molt
Spotting molt in action is just a matter of taking a minute to look carefully at the feathers. Birds in heavy molt tend to be scruffy overall. Look for contrast between new and old feathers, and gaps in their wings where old feathers have been dropped and new ones haven’t grown in yet, like a jack-o-lantern’s gap-toothed smile. See Two Tips for Telling a Bird’s Age by Its Molt Patterns for more on this.
With an appreciation of molting, you’ll see that a motley looking bird in late summer is really another incredible stage of a bird’s life cycle. And you’ll appreciate how birds prepare for the long journeys of their fall migration.