Originally published July 2013; Updated May 2021.
On the dog days of summer, birds seem to disappear – the chorus of dawn subsides and a strange silence spreads in the woods. Many birds look neglected and no longer wear their bright breeding colors. Many bird watchers hang up their binoculars until the autumn migration. (July and August are typically the lowest two months for submitting eBird checklists.)
But there is no need to stop bird watching. The birds are still there, they just hold back because they are replacing their feathers. If you know what goes on in the life of birds after they are brood, you can continue to find species well into summer.
Birds sing for two main reasons: to attract a partner and to defend a territory. Many baby birds in North America are fledged by July, and even birds with multiple nests per year are ready by early August.
Some birds may continue to sing for a while to help their young learn their local singing dialect. But many birds, like the American robin and red-shouldered blackbird, stop holding territory and start joining a flock – and territorial chant just isn’t compatible with the flock. One by one, each species falls out of the morning choir.
Lying low during the Molt
After hatching, the molting season begins, heralding major changes in both the appearance and behavior of the birds. Mauser is the systematic replacement of feathers. All birds do it – from hummingbirds to penguins. They must molt to survive as feathers wear out from abrasion and fading from the sun. Once a year (in the case of temperate species in late summer) birds grow a completely new set of feathers through a complete moult.
When birds develop new flight feathers, they are particularly vulnerable to predators. During their wing-molting, some of their flight feathers are less than full length, creating gaps in their wings that make them less maneuverable and powerful in flight. To avoid the attention of predators, many birds – such as sparrows, warblers, and thrushes – lie low, rarely call, and hide in vegetation.
Drakes go incognito
Photo by Chris Wood
Colorful male ducks have an additional trick to avoid attracting predators’ attention during molting. Waterfowl, including the loons and great crested grebes, lose all of their primary and secondary feathers at once, rendering them flightless for about a month. To help them hide when they cannot fly, male ducks grow a special set of camouflaged feathers called eclipse plumage. In July, you may find that all of the mallards in a local park look scruffy and mostly brown, like they are all females. Shortly after their wing feathers have grown back and they can fly again, drakes will regrow their colorful body feathers.
Groups of birds use different strategies to incorporate molting into their annual schedule. Most songbirds in eastern North America, including the Chestnut-Sided Warbler, Baltimore Oriole, and Indigo Bunting, begin replacing their flight and body feathers shortly after their young flight. They tend to go through this full molt on or near their breeding grounds and migrate south after having a new set of feathers.
However, some songbirds in western North America begin their migration and fly a little south before molting. Western summers can be extremely dry and bleak. Many species – including the Western Kingbird and Lazuli Bunting – embark on a partial migration to the Mexican monsoon region (southeastern Arizona, New Mexico, and northwestern Mexico) to molt. The monsoon rains bring an abundance of insects to feed on. After shedding their flight feathers, these birds continue their migration further south to their wintering areas.
Bird watching during the Molt
Detecting moults in action only takes a minute to get a close look at the feathers. Heavily molted birds tend to be unkempt overall. Look for contrasts between new and old feathers and gaps in their wings where old feathers have been dropped and new ones haven’t yet grown in, like the gap-tooth smile of a jack-o’-lantern. For more information, see Two Tips for Knowing a Bird’s Age by Its Molecular Patterns.
If you appreciate molting, you will find that having a colorful looking bird in late summer is really another incredible stage in a bird’s life cycle. And you will appreciate how the birds prepare for the long journeys of their autumn migration.