Mallards have started to get their green heads back. I welcome the return. A summertime mallard is a pitiful creature.

Male ducks get very colorful during breeding season, when they strive to win the affection of females. This advantage becomes a big disadvantage after mating season. Being big and colorful is an invitation to predators. Bright colors practically scream “eat me.” Worse, ducks molt their flight feathers at this time, so they are flightless for several weeks — sitting ducks, so to speak. Thus, drakes shed their breeding plumage as quickly as possible and turn brown and drab. It’s known as eclipse plumage. For the rest of the summer, they just try to blend in.

Mallards become easily accustomed to people, so there are plenty of opportunities to watch them in large groups. Sorting through the ducks in late summer, trying to figure out the males, females and youngsters, is a challenge.

It’s even harder with teal. Blue-winged teal are smaller than mallards. Green-winged teal are tinier still — only half the size of a mallard. In spring, it’s easy to tell the two teal apart. But in eclipse plumage, they look very similar. I hate that, because everyone in a birding group turns to me and expects me to make an authoritative identification.

If the teal flies or spreads its wings, it’s easy. Even in eclipse plumage, both species retain the wing colors that give them their names. A flying blue-winged teal shows a powder blue patch on the wing. Green-winged teal display the bright green. Sometimes the flash of these colors is visible even on a sitting duck.

Of course, they never make it that easy on me, so I have to look for other subtle clues. The green-winged teal has a smaller, thinner bill. This gives it the appearance of a blockier head. The blue-winged teal has a bit of white at the base of the bill that reaches down to a whitish throat.

I especially pity the male wood duck. His breeding plumage is as showy as any creature God put on earth. But in midsummer, he’s barely got any of that color left. It’s like watching James Bond shed his tuxedo and hang around the couch in old sweats all weekend.

Not that there’s anything wrong with that.

But a curious thing happens in September. Mallards start feeling frisky again and go through another molt to reacquire the breeding plumage they forsook just a short time ago. In this case, they are only changing body feathers. Flight feathers remain. This strategy of shedding colorful feathers while molting flight feathers is uncommon in the bird world. It’s practiced by only a few other species on the planet, and none that you’ve ever heard of. Even geese don’t do it. They molt only once a year.

The timing of this second molt varies by duck species. Mallards are notorious for being aggressive Lotharios, so it makes sense they would want to pretty up as soon as they can fly again. Other ducks may do it on their wintering grounds.

Blue-winged teal are second only to mallards as the most numerous duck in North America. They molt twice but follow a different strategy. Males have no role in raising the young, so they begin to molt their flight feathers early in summer. Because they also are among the ducks that migrate the farthest — as far as South America — males tend to leave Maine as early as possible, even in mid-August. By this time of year, most males already are gone, and the females and youngsters will be departing shortly. They are among the last ducks to return in the spring.

Harlequin ducks can compete with wood ducks in any beauty pageant, but Maine only gets them in winter. They breed in the whitewater rivers of northern Canada, and many spend the cold months in the surf zone of our rocky coast. Like wood ducks, they go through a non-pretty period in summer. Then they molt again before coming to Maine, so we never see their eclipse plumage.

It all has to do with sex. Most waterfowl start forming pair bonds in winter, earlier than most birds. I’ve witnessed copulation between harlequin ducks along the Maine coast, even though they are a thousand miles from where they will nest. The birds that pair up the earliest, molt the fastest. Thus, mallards are getting their green heads back right now. Finally, they can start looking like mallards again.

Bob Duchesne serves as vice president of Maine Audubon’s Penobscot Valley Chapter. He developed the Maine Birding Trail, with information at mainebirdingtrail.com. He can be reached at duchesne@midmaine.com.