Of all the ducks in the Americas that one might encounter, the black-bellied whistling-duck (Dendrocygna autumnalis) no doubt represents the most unmistakable. Seeing them and hearing them makes that clear.
Too early for anything but dim light to have climbed over the horizon, I walked toward Sunset Bay and let my ears guide me to what I already knew must be there: White Rock Lake was hosting a group of these magical beasts. I found them quite easily as they huddled en masse in the bay’s confluence, the whole group chatting away as though the three dozen or so individuals were debating the day’s plans.
Until recently this species could be found in North America only in far southern Texas and down into Mexico. Their historic range extended from there southward through Central America into South America, and they were yearround residents throughout that territory. But in the last few decades these stunning critters have expanded as far north as the Dallas-Ft. Worth metroplex as well as into limited areas in surrounding states.
They are lively birds, talkative and gregarious creatures whose long legs and necks make them look more like geese than ducks. And docile! Oh, they are quite docile, something that made them easy marks for hunters (and probably still does when someone chooses to stalk and kill them).
Rarely do they stay here in North Texas through winter, although that’s not unheard of around these parts. Mostly, they arrive in early spring and leave in late autumn or early winter. Only their northernmost populations migrate, an interesting fact and one I think might change as they settle more permanently into their expanded range.
Unlike many duck species, black-bellied whistling-ducks are sexually monomorphic. This means there’s no need for eclipse plumage. It also means seeing one of them is seeing all of them—an encounter that engenders a desire to see them again and again, to keep seeing them given their fanciful, whimsical appearance that, true to their description, is quite unmistakable.
And seeing them is only half the fun. Hearing them is a world unto itself. They aren’t called whistling ducks for nothing!
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 The quality of the photos is certainly less than I hoped for. Being too dark because of the time of day, I had to settle for these images. There are times when even 400mm doesn’t get me close enough to something, and that never is truer than when it’s dark.
 Sexual monomorphism (the opposite of sexual dimorphism) applies when both genders of a species look identical. Though in the most rigid sense it would hinge on internal anatomy as well as external presentation, a species is generally accepted as being sexually monomorphic when the gender of an individual cannot be determined by its outward appearance. Black-bellied whistling-ducks and northern mockingbirds are good examples of this as the sex of a single bird can’t be determined by physical presence alone.
 Sexual dimorphism applies when a species demonstrates gender-based differences. Ducks usually are good examples of sexual dimorphism: males and females tend to be dramatically different from each other, sometimes in size but most notably in plumage colors and patterns. Adult mallard ducks and northern cardinals are good examples of sexual dimorphism.
 Sexual dimorphism does not always present itself at birth. For example, in canines and primates the physical differences between genders usually are apparent at birth. For sexually dimorphic birds, on the other hand, young often look like adult females because that gender tends to be plain and better camouflaged than adult males. Hence, many juveniles present female plumage until they molt into adult plumage.
 Eclipse plumage is a defense mechanism for many duck species whereby males lose their ostentatious breeding colors and patterns for more subdued female-like plumage. As ducks molt, they lose their flight feathers, hence males brightly colored who cannot fly to escape a predator stand a better chance of being eaten—and bringing a quick death to a species. Therefore, many duck species evolved eclipse plumage as a means to ensure males are less visible and showy while they molt, a time during which they may or may not be able to fly.