Though small, a male in prime plumage has a yellow forehead, black eye mask and back flecked with black and gold, along with — as the name implies — bold stripes of rust red under each wing.

Even the breeding female, though more muted, boasts touches of yellow and the red streaks.

Yet this girl, picking off bugs in an apple tree, definitely was having a bad hair day. The head and body looked to be a little moth-eaten and missing feathers.

Yet it’s not a sign of parasites or poor nutrition — this warbler is just molting.

A FEMALE CHESTNUT-sided warbler shows signs she’s going through her summer molt in preparation for the fall migration. (Betsy Bloom/Daily News photo)

When the breeding and nesting season ends in mid- to late summer, a number of birds swap out the colorful or distinctive feathers that can help attract a mate for a more modest look heading into fall migration.

It can make for bare-headed cardinals that look a little like mini-vultures at the backyard feeders, or blue jays that seem to have lost their crest.

For warblers — and buntings and tanagers, too, according to the Cornell Lab of Ornithology’s All About Birds website at www.allaboutbirds.org — this will be a complete molt, after which the chestnut-sided will morph “into lime-green and grayish white plumage with a distinctive white eyering” before heading to the “thickets, shade-coffee plantations and second-growth forest in Central America.”

The warblers then in spring will have a partial molt that restores those colors for the next breeding season.

Other birds — chickadees, hawks, hummingbirds, jays, woodpeckers, to name a few seen in the region — may have only one complete molt each year, according to Cornell. A few do two complete molts but that seems rare.

Waterfowl also undergo a molt in summer, but it’s a different matter — unlike the songbirds, species such as mallard ducks and Canada geese will drop their primary flight feathers all at once, leaving the birds grounded for 20 to 40 days. Since they still can swim, they manage to stay relatively safe despite not being able to fly.

After this molt, mallard males will be in “eclipse” plumage, looking much like the females, which is by design — they blend in better while flightless. Come fall, the drakes will have a second molt that restores the green head and other familiar markings.

For the common loon, however, the gray-brown eclipse look that comes when they molt in fall will stick through winter. Also different from the ducks and geese, loons have their flightless period in midwinter.

That’s when the loons are settled into large bodies of water — in this region, Lake Michigan is a common wintering site — where, again, they can be safe, relatively undisturbed and have access to food while molting.

“It takes a lot of energy to build new feathers,” the Cornell Lab website explained. “As a result, timing is important — and birds typically time their molts to avoid other periods of high energy demands, such as nesting or migration. Molt timing can be more complicated for larger birds, because growing larger feathers means that their molt process takes longer than it does for smaller birds.”

So worry no more about the tattered appearance of some of the songbirds out there. It’s not a sign of poor health, but an indication fall migration isn’t that far off.

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In fact, some birds already have begun the journey, difficult as that is to hear.

Shorebirds each summer start the movement, with adults leaving northern breeding grounds in July and now the juveniles following suit, said Ryan Brady, Natural Heritage Conservation Program biologist for the Wisconsin Department of Natural Resources. Their numbers should peak later this month, he said.

“Look for these long-distance migrants in flooded fields (a.k.a. “fluddles“), exposed shorelines and drying wetlands,” Brady said in his statewide birding report Monday.

Male ruby-throated hummingbirds also may start migration in the early part of this month — but keep those feeders up, as the females, fledglings and others from the north will work their way through the region well into fall.

And as always when birds get to moving, watch for wanderers that stray off course, Ryan advised.

“Case in point, this week’s rarest bird in the state was a Mexican violetear found on August 2-3 in Crawford County (Wis.), marking the eighth state record of this large, dark green hummingbird typically found in Mexico and Central America!”

Another unusual sighting was a swallow-tailed kite in Schoolcraft County on Aug. 2, a falcon-like, black-and-white bird with — again, as the name implies — a long, deeply forked tail. It’s native to the southern states.

Another kite was reported in Lincoln County in northern Wisconsin. It’s unclear whether this is just young birds dispersing or possibly an effect of the tropical storm that moved up the East Coast earlier in the week.