Roger Tory Peterson coined the term “confusing fall warblers.” I grew up with a copy of his field guide in my hip pocket. For decades, everything I knew about birds was contained within the pages of his book, which was first published in 1934. Ever after, I took it as an article of faith that warblers were supposed to be confusing in autumn.
Oh, sure, most black-throated green warblers don’t have a black throat in September. Magnolia warblers look a bit mysterious. Blackpoll and bay-breasted warblers change color completely. Yellow-rumped warblers may as well be called yellow-rumpled, so ugly and variable is their fall plumage. But most warblers retain enough of their breeding characteristics to be identifiable. I don’t find them confusing.
I have come to realize that Peterson erred. He should have included a section on confusing fall ducks. Waterfowl arrive on their spring breeding grounds in spectacularly colored plumage, each species more wondrous than the last. But by autumn, every duck looks like a female mallard: dull, brown and streaky.
Fortunately for hunters, a flying duck is still generally easy to identify. Mallards have white in the wings. American black ducks don’t. The flash of green in the wing of a green-winged teal is easy to distinguish from the powder blue patch that adorns the wing of a flying blue-winged teal. But collect these ducks together on the back edge of a marsh and they all look alike. If it weren’t for a slight size difference, I’d struggle to distinguish between a blue-winged and a green-winged teal, even if the two were sitting on my lap. They’re just mini-mallards in September.
All birds molt, but each molts differently. Raptors replace their flight feathers one at a time so that they can keep hunting. Songbirds replace their feathers in small bunches, shedding their body feathers in late summer, but sometimes keeping their flight feathers longer. Ducks, however, molt all at once, and do so as rapidly as possible. That makes them flightless for a period in summer. Unable to fly from predators, they take on the brown, streaky coloration of female mallards, and depend on concealment for safety. This basic plumage is called eclipse plumage, and it makes duck watching a real challenge in late summer.
Fortunately, this eclipse plumage doesn’t last long. New feathers may help with the rigors of migration, but ducks begin to pair up again in late winter, and that means they need their mating colors back sooner than most birds. A second molt restores their breeding plumage before spring. Ducks are unusual in that they molt twice in a relatively short period of time.
To improve your duck identification skills in autumn, first determine if your mystery duck is a dabbler or a diver. Dabbling ducks tip up, reaching underwater to feed. Diving ducks dive. Typical diving ducks are ring-necked ducks, mergansers, goldeneyes and ruddy ducks. Females of these species may pose a challenge, but generally they are not too difficult to distinguish. Dabbling ducks are the real ID troublemakers.
To identify a dabbler, start with mallards and American black ducks. Male mallards lose the green color in their heads and resemble drab females in late summer, but in every case, mallards are a lighter shade of brown than American black ducks. Both ducks are similar in size and are significantly larger than other ducks likely to be in Maine.
So, when you observe a mystery dabbling duck, determine if it seems smaller than a mallard. In comparison, wood ducks, northern pintails, northern shovelers and American widgeons are smaller. The shape of each is unique. The head of a wood duck appears square, sitting on a relatively thin neck. The neck of a pintail is long, slender and elegant. Shovelers in autumn look much like a small mallard, but the bill is immense. Widgeons have shorter, thinner bills than mallards.
Teal in autumn look much like tiny female mallards. The green-winged teal is half the size of a mallard and the blue-winged teal is not much bigger. Green-winged teal are about the same color as female mallards, a relatively warm brown. Blue-winged teal are grayer-brown and have a small area of whiteness at the base of the bill.
It’s hard being a duck. Waterfowl quickly learn where they are safe from hunting, which is often in city wetlands. When it’s time to practice duck identification, don’t be surprised if there are cooperative ducks right around the corner.
Bob Duchesne serves as a Maine Audubon trustee and vice president of its Penobscot Valley Chapter. Bob developed the Maine Birding Trail, with information at mainebirdingtrail.com. Bob can be reached at duchesne@midmaine.com.