Key Traits
Douglas Adams once wrote: “If it looks like a duck, and quacks like a duck, we have at least to consider the possibility that we have a small aquatic bird of the family Anatidae on our hands.”
This was Adams’ twist on the well known Duck Test. This test relies on the assumption that we are familiar with what ducks look and sound like. It’s safe to say that most of us are.
But people sometimes confuse other water-loving birds like coots and grebes for ducks. These are most definitely not ducks and not members of the duck family. Not even close. Grebes, coots, and loons each belong to their own families, none of which is closely related to Anatidae.
What key characteristics are shared by ducks, geese and swans? For starters, these birds are mostly aquatic, spending much of their time swimming in, or at least near, water. We often refer to them as waterfowl. But waterfowl is not a scientific word. Some people lump unrelated birds into this category—birds like those grebes, coots, and loons. Used that way, the word ‘waterfowl’ doesn’t correspond to any real biological group of birds. The same thing is true for the word ‘raptor.’ But we’ll leave that one for another blog.
Anatids—that is, birds in the family Anatidae—have bodies that are either ovoid, which means egg-shaped, or fusiform, which means tapering at both ends, like a spindle.
The smallest anatid is the African Pygmy-Goose (Nettapus auritus). This little bird is adorable, but also beautiful. The male has a chestnut breast and flanks, black and iridescent green upperparts, and a white-and green-head. It’s only about 12 inches or 30 centimeters long. You’ll find African Pygmy-Geese floating around in the swamps and shallow lakes of sub-saharan Africa.
The smallest species in both North America and Europe is the Green-winged Teal (Anas crecca). At 14.5 inches or 37 centimeters, this duck isn’t much bigger than the pygmy-goose.
The colossus of the family Anatidae is the Trumpeter Swan (Cygnus buccinator). This elegant North American bird is about 4.8 feet or 1.47 meters long. That measurement includes the bird’s super long neck. The Trumpeter Swan is also heavy, for a bird anyway, weighing in at about 30 pounds or 13.6 kilograms. Not only is this beast the largest member of its family, it’s also one of the heaviest flying birds in the world.
Ducks, geese, and swans have small heads relative to their bodies. And their necks are long. The number of cervical vertebrae—the spinal column bones in the neck—varies across the avian world and among the birds within the family Anatidae. Swans have 24 or 25 cervical vertebrae; geese have between 17 and 23; ducks have fewer than 16.
How many neck vertebrae do you and I have? Pretty much all mammals have the same number of cervical vertebrae: 7. So, believe it or not, humans have the same number of neck bones as whales, bats, and yes, even giraffes.
The beaks—the bills—of anatids are one of their most recognizable features. Especially the bills of ducks. Many members of this family have the classic flattened, sort of spatula-shaped bill. But there are also variations on this basic model.
Most ducks, geese, and swans use their bills to chow down on plants of one kind or another. So they’re generally herbivorous. But you won’t be surprised to hear that there is a fair amount of dietary variation among species. Not all of them are herbivores. Some of these birds specialize in catching animal prey like fish. Others fall within the more omnivorous part of the spectrum, adding some small invertebrates to their plant-based diets.
The wings of anatids are relatively short and pointed. They allow for fast, strong flight. Ducks and their relatives need to flap almost constantly while in flight, since their short wings don’t allow for much gliding.
Some duck species that feed at the surface or in very shallow water can take off explosively from the water. Their powerful pectoral muscles, which drive the wings, make this possible. Other species need to get a sort of running start across the water’s surface before they can get airborne.
Now I’m sure you know the expression “Like water off a duck’s back.” These birds really do have remarkably watertight plumage. As aquatic birds, ducks and other anatids need to prevent water from soaking their insulating down feathers. Because down loses its ability to keep a bird warm if it gets wet. The outer contour feathers overlap to form a sort of shell to keep water out, like a Gore-Tex rain jacket. Contour feathers have a fine-scale structure that causes water to form beads and just roll off. This waterproofing is enhanced and maintained by oils from the bird’s uropygial or preen gland (see the blog[link], Feathers: Form and Function).
The plumages of birds in this group are most often some combination of brown, gray, black, and white. But there are many species that are much more colorful. This is particularly true for male ducks. A few of the most attention-demanding examples are the Harlequin Duck, the Wood Duck, and the Mandarin Duck. The latter two birds are close relatives, both belonging to the genus Aix. The male Mandarin Duck is really ornate! Its plumage is a gorgeous patchwork of orange, blue, purple, black, white, cream, and green feathers.
Birds, in general, replace their feathers once or twice a year. This is the process of molting. The ability to fly is so crucial to birds that most of them molt—or shed—only a few wing or tail feathers at a time. That way, they maintain their ability to fly.
But anatids shed their primary wing feathers all at once in the fall. That means these birds are grounded, unable to take to the sky. This lasts for about a month, during which the birds are vulnerable to predators. So ducks, geese, and swans tend to lie low at that time of year. They keep out of sight until their new wing feathers grow in.
This trait isn’t unique to birds in the family Anatidae. Some other water-dwelling birds like loons and grebes also molt their flight feathers all at once.
What sounds do these birds make? Well, they definitely aren’t songbirds, taxonomically or figuratively. They don't sing, and few would describe their calls as “melodious.” Compared to songbirds, most ducks, geese, and swans don’t vocalize all that much. The sounds they do make are relatively harsh, like the grunts, honks, quacks, and whistles. I don’t know about you, but I still love hearing these sounds.
The famous American explorers Lewis and Clark had something to say about the sounds of waterfowl. In his journal entry for November 5th, 1805, Captain William Clark wrote “...rain continues this morning, I slept but very little last night for the noise kept during the whole of the night by the Swans, Geese, White and Grey Brant Ducks, on a small Sand Island close by. They were immensely numerous, and their noise horrid.”
Family, Diversity
Family
Several major divisions have formed within the family Anatidae over its long evolutionary history. A few of these distinct genetic lineages are treated as subfamilies. Most species belong to one of two subfamilies: Anatinae or Anserinae. Notice the suffix for subfamily here is “nae.”
The subfamily Anatinae includes most of the birds that you and I call ducks. The other major subfamily, Anserinae, includes most of what we call geese as well as all of the swans.
In addition, there are some ducks that don’t fit into the Anatinae or Anserinae subfamilies. Like the 8 species of whistling ducks all belong to the genus Dendrocygna, or the 6 birds in the genus Oxyura, including our familiar Ruddy Duck. Those birds, too, stand apart in their own group. And, if anything, these Oxyura ducks are more closely related to swans and geese than other ducks. The point here is that the birds we call ducks, geese, and swans do not fit neatly into their own respective subfamilies.
As is often the case, the common names we use do not reflect the reality of nature. They don’t necessarily conform to the real genetic, evolutionary relationships among birds.
The problem with common names might deserve its own blog, so I won’t get all riled up about it right now, but I will give you an example of what I’m talking about. The Blue-winged Goose is a chunky, grass-munching bird that lives in high elevation meadows in Ethiopia. To me, it’s facial expression looks innocent and sweet—like a gosling that never grew up. You would probably agree with me that this bird looks like a goose. But its closest relative is actually Hartlaub’s Duck, of western Africa. All the Blue-winged Goose’s close relatives are called ducks. Genetically and therefore taxonomically, this bird sits squarely within the subfamily Anatinae. Recall that this is the group that includes most of the world’s so-called ducks.
So what the heck is a duck and what is a goose… like, really? Honestly, I can’t give you a simple answer. There doesn’t appear to be one sharp dividing line between these birds at the genetic level. Over millions of years, duck-like birds and goose-like birds have evolved more than once, independently, within the Anatidae family. If I was renaming birds in this family, I would maybe try to simplify things and just call them all ducks.
In practice, the birds we call ducks tend to have the classic, flat “duck” bill. They have shorter necks, and they usually show distinct plumage differences between the sexes. The birds we call geese have deeper bills more suitable for grazing than dabbling. Geese show few if any differences between males and females, and they often form long-term bonds with their mates.
Now what about scoters, teals, scaups, hardheads, goldeneyes, eiders, smews, pochards, mergansers, wigeons, pintails, garganeys, shovelers, and so on? These are just different types of ducks. Each of them has distinguishing physical features and behaviors. And each has its own charms.
The common names here—teal, scaup, etc.—mostly correspond to one or more genera. So for example, the 6 scoter species are all ducks in the genus Melanitta.
Then we have “dabbling ducks” and “diving ducks.” I’m sure these terms are familiar to you. They describe feeding behaviors. So they’re helpful for identifying ducks in the field. If you see a duck disappear underwater for a few moments, then pop back up like a cork, that narrows down the list of possible species. You know it's probably one of the diving ducks.
But the terms “dabbling duck” and “diving duck” do not correspond very well with any real genetic lineages in ducks. Some might argue with me on this point, but I’ll just leave it at that for now.
Dabbling ducks like the Mallard and Northern Pintail tend to forage in shallow water. As they munch aquatic plants below the surface, their feathered duck butts tip up to the sky. These dabblers rarely completely submerge themselves.
Diving ducks, on the other hand, swim around underwater as they hunt for plants or animal prey. They spend more time in deeper water. Examples from this group include scaups, goldeneyes, the Common Pochard, and the Bufflehead.
Diversity
With about 165 species of ducks, geese, and swans, the family Anatidae is pretty diverse. Let’s talk a little about this group’s diversity, distribution, and evolution.
As a group, these birds are cosmopolitan. We talked about that word in the blog about the Peregrine Falcon. A cosmopolitan species or family lives pretty much all over the world. Anatids are indeed widespread. You’ll find them everywhere except in the heart of the Sahara Desert, the interior of Greenland and Antarctica. I should point out that very rarely Black-necked Swans show up at the northernmost tip of the Antarctic Peninsula. This species normally breeds in southern South America. But looking at data in eBird, this species was reported in Antarctica only once, in 1995. There were two of them and they both died. Sad, I know.
I want to tell you about another bird that died in Antarctica a few years earlier… actually about 67 million years earlier. In 1992, a fossil bird was found on the Antarctic Peninsula, on Vega Island. Paleontologists eventually gave it the genus name of Vegavis.
Vegavis appears to have been a diving bird, and its closest living relatives are our ducks and other anatid buddies. In case you’re wondering, Antarctica back in the day wasn’t all frozen and barren. 67 million years ago, it was still part of the supercontinent Gondwana. It was covered in forests and crawling with dinosaurs.
The discovery of Vegavis was enormously important in the field of ornithology. It provided the first fossil evidence that some modern bird lineages started to diversify millions of years before the big extinction that killed off the other dinosaurs.
Most of the bird orders and families we know today trace their origins to the crazy times after the asteroid hit Earth 66 million years ago. But now we know for sure that some relatives of ducks were waddling around in the Cretaceous Period, in the shadows of Tyrannosaurus and Triceratops.
One big take-home message here is that the ducks and other birds we’re talking about today represent an ancient bird lineage. Birds like these have been around a long, long time.
From their southern origins in Gondwana, anatids spread northward in the last 25 to 30 million years, making their way across the planet. Today, these birds occupy a wide variety of freshwater and marine habitats. You’ll find them grazing on the tundra, in alpine meadows, and on golf courses. You’ll see them paddling around in swamps, estuaries, lakes, ponds, billabongs, bays, rivers, and often in your local sewage treatment plant.
Bills, Diet, Foraging
Picture the classic duck’s bill with its flattened shape. If you’re imagining a Mallard, I’m right there with you. It’s a splendid example. Maybe you recall that the scientific name of this species is Anas platyrhynchos. Platyrhynchos translates as “flat bill” or “flat snout.”
What is the advantage of this bill shape? How does it work? The basic mechanism works like this: a duck sticks its head into water or some stinky mud to feed on small plants, seeds, or invertebrates. It opens and closes its bill rapidly, but not very widely. Water or mud and any food items enter the bill near the tip. This material gets sucked into the mouth and then exits out the sides, closer to the bill’s base.
Lining the inside edges of the upper and lower bill are dozens of small, blade-like structures called lamellae. These lamellae are packed close together. As water leaves the bill, food items get trapped in the lamellae. This is similar to how baleen works in the mouths of whales.
So a duck’s bill is a filter feeding apparatus. These birds strain their food from water or mud. As a generalist omnivore, the Mallard eats many things, not just tiny, filterable tidbits. It will also eat large insect larvae, worms, snails, crayfish, leaves, roots, rice, wheat, corn, and so on. And a Mallard will happily scarf down just about anything a human will toss at it: bread, watermelon, tater tots, whatever.
Another interesting feature of duck bills and those of geese and swans is they have a soft, rubbery outer layer. This outer sheath of keratin, called the rhamphotheca, is hard and horny in most other birds.
Anatids all have a small, hard projection at the tip of their upper bill. We call this the nail. It functions sort of like a claw or fingernail, allowing the bird to more easily grab stuff.
Underneath the nail, there are rows of tiny nerve receptors called touch papillae. Collectively, these papillae form the bill tip organ. This sensitive organ allows ducks and other anatids to feel around in the mud or in murky water to find goodies with their sense of touch alone.
Among duck species, there are many variations on the standard issue duck bill, some more dramatic than others. It all depends on what a species eats.
I’ll highlight a few examples. First, we have the 5 species of mergansers. These ducks have long, thin bills with serrated edges. This is a major departure from the normal duck bill shape. Mergansers eat mostly small fish. Those serrations on their bills help them hold on to their slippery, thrashing prey.
Then there are the scoters. These are ducks that spend a lot of time in coastal marine waters. They specialize in another type of animal prey: mollusks and other marine invertebrates. These ducks dive beneath the waves to scoop up clams and rip mussels off of rocks. Their bills are thick and strong. But they don’t crush the shells of their prey with their bills. They just swallow them whole.
The four species of Steamer-Ducks are South America’s answer to the scoters. Steamer-Ducks are chonky coastal birds that scoop up marine invertebrates with their thick bills. Interestingly, three of the four species are flightless.
The last example of a not-so-average-duck is the Pink-eared Duck of Australia. This bird is an oddball—both in the way it looks and in the sense that ornithologists haven’t quite figured out how it’s related to other members of the Anatidae family. The Pink-eared Duck has a long, flat bill. Near the tip of the upper jaw, a rubbery flap of skin dangles conspicuously from each side. These birds are primarily filter feeders that eat microscopic algae and other tiny things in the water. Ornithologists don’t know for sure what those flaps do, but most likely they help the ducks find food with sensitive touch receptors. I’ll include a photo of this weird, wonderful bird in the show notes for this episode on the website.
I should also mention another filter-feeding duck: the Northern Shoveler. This bird is widespread across the Northern Hemisphere. It has a massive schnoz… a really long, wide bill. The Shoveler uses its bill to strain tiny crustaceans from the water as it motors along on the surface.
Okay, before we move on to talking about breeding in anatids, I want to make sure I don’t completely neglect our friends, the geese and swans.
Geese and swans are primarily herbivores. Their bills tend to be deeper than those of ducks—more arched, less compressed from top to bottom.
Swans forage in several ways, including dabbling at the surface and plucking aquatic plants underwater while upended. They take advantage of their long necks to reach down into the depths.
The several independent lineages of birds we call ‘geese’ are almost all grazers. They tend to forage while walking around on land. The Greylag Goose, for example, eats grass, roots, leaves, grain, and many other plant foods.
Breeding
Once a year, ducks, geese, and swans breed. To accomplish this task, they form monogamous breeding pairs. But there’s some variation in the degree of monogamy in this family. Swans are the most loyal, usually mating for life. Many geese do this, too. In these birds, both males and females help raise the young.
In some other species, monogamous pairs stick together for only a few years. And many ducks are monogamous through a single breeding season only, seeking a new partner each year.
Sexual dimorphism is common among ducks, but mostly non-existent in the geese and swans. Sexual dimorphism is where males and females have different forms, or morphs.
In the breeding season, many male ducks have brighter, more showy plumages than their female counterparts. Like the Mandarin Duck I mentioned earlier. Males can also have various ornaments, like long tail feathers, bright patches of skin, and even weird growths on their bills.
For example, males of the Knob-billed Duck and its close relative the Comb Duck have an enormous fleshy crest thingy growing from the top of their bill.
The bright colors and wacky ornaments of male ducks result from millions of years of females choosing to mate with males that have such traits. This is classic sexual selection. We’ll definitely do a whole blog on sexual selection at some point. It’s fascinating stuff.
So our fancy looking male ducks try to win the attention of females. But they don’t just float around on the water passively, looking pretty.
Courtship is usually a more active affair. Males use courtship display behaviors to win the hearts of females. And females, too, show courtship behaviors.
Wood Ducks, for example, display numerous courtship behaviors. Some are unique to the colorful male, others are used by only the female. And some are used by both sexes. Here are the descriptive names for some of these behaviors in Wood Ducks: Turn-the-back-of-the-head, chin-lift, display shake, rush, bill-jerk, and burp.
In the Wood Duck and other species, different behaviors are used depending on the stage of courtship. Some behaviors initiate the pair bond, others are used later to strengthen and maintain it.
Now, I’m about to talk about bird sex, briefly. This is The Science of Birds, after all, and we don’t want to shy away from this topic. It’s so important, biologically.
There are some really interesting things about the sex lives of birds in the Anatidae family. I’ll highlight only one now, since we don’t have time to go into all of it. Among all the world's birds, most males don’t have anything that resembles a penis. They just have a cloaca that seems pretty similar to that of the female. The cloaca is the single opening at the back end of a bird where wastes come out and where copulation takes place.
But about 3% of bird species do have a penis. It’s not at all the same thing as the organ found in mammals. It evolved independently as an extension of the cloaca. Technically, it’s called a cloacal phallus. Most of the world’s bird species that have this organ are ducks and geese. Depending on the species, the male’s cloacal phallus might be short or it might be long. Like, really long.
In fact, the Lake Duck (Oxyura vitatta) has the longest phallus relative to body size of any bird. This close relative of the Ruddy Duck lives in South America. The bird’s body is about 23 inches or 59 centimeters long. Its cloacal phallus is more than half as long as its body. The longest on record, that I know of, is 16.7 inches, which is 42.5 centimeters.
If most birds don’t have or need a phallus, why do many ducks and geese have this structure? And why are some so dang long? One hypothesis offered for a long time was that the phallus is an adaptation for mating in the water, which is what many of these birds do. That seems like a reasonable explanation. More recently, however, ornithologists have come up with some hypotheses that are far more complicated and, I think, more interesting. But we’ll leave that topic for another day.
Okay, so our birds have mated, eggs have been laid, and it’s time to raise a family. For species like swans and many geese, both parents will take part in caring for the youngsters.
This isn’t the case for many ducks. The rule of thumb seems to be that in species with strong sexual dimorphism, dad doesn’t stick around. Those flashy, colorful males might help the female build the nest or protect her and the eggs for a little while. But these males usually drift off once incubation is well under way. This makes some sense: since a male is super conspicuous, he might attract predators to the nest if he stayed close to his family. Females, on the other hand, have cryptic plumages… they’re camouflaged as they sit in their nests.
This might explain why even male Harlequin Ducks don’t stick around to raise their ducklings. You see, Harlequin Ducks are abnormal because they form long-term pair bonds, unlike most duck species where the male has such showy plumage. The same monogamous pair of Harlequin Ducks meets up year after year to mate. Males in long-term pairs in other species, like geese, usually stick around to raise their babies. Maybe the highly conspicuous male Harlequin Duck would endanger his family if he stuck around. Predators would see him a mile away. So he leaves his family behind, then reunites with his lady the next season.
Baby ducks, geese, and swans are not only adorable, but also capable of feeding themselves not long after busting out of their eggs. And they can swim right away, too. So these young birds are precocial. They’re born covered in fuzzy down with their eyes open. They’re ready to follow Mom all over the place.
Sometimes the young of several families will gather together in one group. One or a few adult birds will take care of the entire gang of babies. Sort of like day care. Ornithologists call this a crèche. The phenomenon of crèching behavior is seen across the avian world, from flamingos and penguins to boobies and terns.
A couple years ago, a female Common Merganser made the headlines here in the US when she was spotted with a crèche of 76 ducklings in her care. 76! She was swimming around on a lake with a long line of fuzzy ducklings in tow. Crèches are not necessarily rare in this species, but no one had ever seen a single female taking care of so many young. Who knows what happened to the other Merganser mothers? And good thing the ducklings could feed themselves, otherwise there’s no way this would work.
After a month or two, young ducks, geese, or swans will fledge. In many duck species, parents abandon their young not long after fledging. The parents of some larger species like geese and swans will stay with their offspring through the young birds’ first migration and winter.
If they’re lucky, many species of wild ducks, geese, and swans can live for over 30 years.
Migration
The ‘V’ formation of migrating geese, ducks, and swans is an icon of nature across the world. This behavior helps the birds conserve energy on their long-haul flights. Each bird flies slightly higher than the one in front of it. The movement of air over the wing of the bird in front reduces drag on the bird behind. The bird at the very front doesn’t get this benefit, of course. So when the lead bird gets tired, it falls back, and another takes its position.
Migration is common in this family of birds. Many migratory species breed in temperate or polar latitudes, either north or south. The days are long there and food is plentiful. But when winter comes, their watery habitats freeze over and/or food becomes scarce. So they gather in flocks and fly to warmer places. They find ice-free wetlands, lakes, or bays to spend the winter. It's during this time that males of many species take on their colorful breeding plumage and courtship begins.
Remember that these birds molt their primary wing feathers all at once, after the breeding season ends in the fall. They become flightless. Many male ducks at this time wear a short-term, drab, camouflage plumage. It’s called eclipse plumage. This helps the flightless males hide from predators when they’re so vulnerable.
Flightless birds obviously can’t migrate. What many species do right after the breeding season is fly to a haven, a sort of protected staging ground. Then they molt their flight feathers. After a month or so, they have shiny new primary feathers and they complete their migrations, flying onward to their wintering range.
Birds that do this are called molt migrants. The Surf Scoter, for example, is one duck that does this. After breeding, these birds migrate to distinct molting sites, mostly in coastal waters. I did an entire blog on migration so you can check that out to learn more.
Conservation
For thousands of years, humans have been hunting these plump, greasy birds for food and feathers. Since the year 1500, we’ve been responsible for the extinctions of 7 species in this family. In every case, hunting was to blame.
The most recent extinction was of the Labrador Duck, a sea duck that lived off the east coast of North America. It was last seen in New York in 1878. This was the first bird species to go extinct in the New World after Columbus landed here.
Across the world today, there are 6 critically endangered species in this family, as well as 7 that are endangered and 18 that are vulnerable. Those are categories from the IUCN’s Red List of Threatened Species. So this means that about 18% of the birds in this family are globally threatened.
Hunting is a threat to almost all of these Red List species. But overall, ducks, geese, and swans face many other pressures, too, including habitat destruction, pollution, and invasive species.
Many efforts are being made by government agencies and conservation organizations around the world to protect threatened waterfowl.
One interesting success story comes from the work of Ducks Unlimited here in North America. This non-profit organization has been around since the late 1930s. It’s mission is to conserve habitat for waterfowl and whatever wildlife shares that habitat. Ducks Unlimited has conserved almost 15 million acres of wetland and grassland habitats in Canada, the US, and Mexico. That’s about 60,700 square kilometers. Pretty impressive.
But here’s the catch: the almost one million members of Ducks Unlimited are overwhelmingly waterfowl hunters. The underlying motivation for the organization to preserve habitat is to make sure hunters have a steady supply of birds to blast out of the sky with shotguns.
In case it’s not obvious, I’m not a big fan of hunting for sport. But my personal feelings aside, I think this represents a challenging ethical dilemma in the world of conservation. It’s similar to how trophy hunting for rhinos and other African megafauna can supposedly raise funds for the conservation of those animals.
Ducks Unlimited has without question helped many populations of anatid birds. And as a byproduct of protecting bird habitats, this organization has helped hundreds of other wildlife species. I’ve certainly spent plenty of time enjoying the birds and natural wonders of places protected with the help of Ducks Unlimited.
Under this model of conservation, many bird populations benefit from habitat protection. But the price of that protection is the killing of countless individual birds. The birds shot by hunters are sort of “taking one for the team.” Not that the birds have a say in the matter.
For what it’s worth, I’m conflicted about it. As much as I hate to see any animal killed, I see both pros and cons to this approach. It’s definitely better than the usual human method of operation: destroying wetlands and killing birds with no restraint... for fun and profit, like there’s no tomorrow.
It would be nice if we would pour this amount of money and effort into protecting wild animals and natural ecosystems simply because we value them for their own sake. For their intrinsic worth. Rather than treating them as something for people to use as a resource.
I know I’ve gone off on a tangent. But I think this is important stuff to think about. And the inspiration for this tangent was ducks. So there you go.
One way or another, we need to protect our planet’s 165 wonderful duck, goose, and swan species. The world is a much better place—and a much noisier place—with them in it.