Hello and welcome. This is the Science of Birds. I am your host, Ivan Philipson. The Science of Birds podcast is a lighthearted exploration of bird biology for lifelong learners. This is episode 105. It's all about a small group of birds called mergansers. These are diving ducks known for their skill at catching fish. They have long, slender bills with serrated edges, earning them the nickname Sawbills.
When I think about mergansers, the first thing that flashes in my mind, besides that thin serrated beak, is the image of a common merganser flying swiftly along the course of a small river, flying low just above the water. like it's on a very important mission and it ain't got time to waste. The common merganser is large for a duck, and the male in breeding plumage is pretty unmistakable.
He's got a white body with black accents, and his head is a dark, glossy green. Maybe you're familiar with these birds, too. Maybe you're already a big fan. Or maybe you didn't even know they existed until just now. Either way, our goal today is to learn a lot more about common mergansers and their close relatives. There are five species that we call mergansers. And there's another species in this group that's called the smew.
That's S-M-E-W. The SMU is sort of an honorary merganser. The six species we're looking at today are divided among three genera. We'll talk a little more about that later. Of all the ducks in the world, mergansers are among the species that depend the most on fish. So, not surprisingly, they're excellent divers and swimmers.
There's this video, this meme, of what I think is a juvenile common merganser. I've seen it pop up on YouTube and Instagram and whatnot. In the video, this person is holding the young bird in one hand. They gently set it down on the bank of a river. As soon as it realizes that it's free, the little duck bolts into the water and takes off, paddling frantically like a speedboat along the surface of the water. It's gone in an instant.
It's amazing and honestly pretty funny. I'll put a link to the video in the show notes. But yeah, it gives you an impression of how great mergansers are at getting around in water. All right, let's go ahead and get into it. First, we'll check out what mergansers look and sound like. Then we'll consider their diversity, distribution, and habitats. And much more!
The body shape of a typical merganser is very much like your standard duck. But a few of them, especially the common merganser, have bodies that are more streamlined. Slightly torpedo-shaped, you might say. Two of the six species, the hooded merganser and the smew, have more compact bodies. These two birds are also the smallest in the group. The larger merganser species have some features that are convergent with those of other diving, fish-eating birds, like cormorants and loons.
All these birds have a streamlined form and their feet are positioned more or less at the back of their bodies. Their webbed feet work sort of like the propeller of a boat, propelling them through the water at high speed. But being awesome at diving and swimming comes at a cost. The posterior position of their feet makes mergansers, loons, and cormorants pretty useless for walking around on dry land.
Grebes also fit into this category of aquatic birds that suck at walking. It's the beak of a merganser, however, that really sets it apart from other ducks. Let's take a few minutes to look at this thing. Unlike your classic spatulate bill of a typical duck, a merganser's bill is long, slender, and hooked at the tip. It looks much more like the bill of a cormorant.
But unlike cormorants and unlike loons, mergansers have wicked little teeth running along the inside edges of the upper bill and the lower bill. And when I said teeth just now, you probably couldn't see me making air quotes. Because we all know birds don't really have teeth teeth, right? The way mammals and reptiles do?
So in mergansers, instead of calling the small hook-like structures running along the bill teeth, we should call them serrations. The red-breasted merganser even has the scientific name mergus serator. The serrations of all mergansers are made of the protein keratin, just like the rest of the outer sheath of the bill. Remember that the general term for the keratin sheath of a bird's bill, its beak, is the rhamphothica.
Anyway, the serrated bill of mergansers is, of course, an adaptation for catching and holding on to slippery fish. Mergus serator, the red-breasted merganser, is arguably the most highly adapted as a fish eater. It has the narrowest, most cylindrical bill of all merganser species. Many other kinds of ducts have comb-like ridges of keratin on the inner edges of their bills. They're relatively blunt and rounded, however. These structures are called lamellae.
They're used by ducks as a sort of filter for feeding on tiny aquatic plants and animals. Most waterfowl have lamellae of some kind. So my guess, my hypothesis is that the serrations on the bills of mergansers evolved from lamellae. In evolutionary biology terms, we'd hypothesize that merganser serrations and the lamellae of other ducts are homologous structures.
that they're both derived from a structure found in the common ancestor of these birds, even if they have different functions today. The classic example of homology in vertebrate animals is the forelimb. The front limb or arm of a mammal is homologous with a bird's wing. These two things, these appendages, evolved from the same original structure.
But I'm not sure if ornithologists have really figured out that the serrations of our mergs are truly homologous with the lamellae of other ducks. It could be that these two structures evolved independently. The hooded merganser, which is the only species in the genus Lophidites, has serrations that aren't all that sharp. The tooth-like structures on the bill of a hooded merganser are more rounded or squared off.
they're not so pointy. Compared to other mergansers, the hoodie eats many more crunchy invertebrates, like aquatic insects and crayfish, so its bill may work a little differently. I mean, if you had to choose which kind of merganser to insult or harass, which species to incur the wrath of, my suggestion is that you go with the hooded merganser.
First of all, it's small and weak compared to most of the other species. And with those blunt serrations on its bill, a hooded merganser almost never draws blood when it attacks and bites you in the arm or on the neck. It only pinches a little bit. You can just laugh it off. So you can go ahead and keep trash-talking the bird, insulting its mother and whatnot, without fear of repercussion.
Anyway, the tip of a typical merganser's upper beak, the part we call the nail, is hooked. Again, this is an adaptation that helps with nabbing fish. In terms of bill color... Three species have reddish-orange bills. That's true for the common red-breasted and scaly-sided mergansers. The other three species have grayish-black bills. The common merganser is the largest of the six species. Male common mergansers are a bit larger than females at about 26 inches or 66 centimeters long.
By comparison, your standard-issue mallard duck is a few inches smaller than a common merganser. The Brazilian merganser is the next largest, followed by the scaly-sided merganser. The smallest two species are the hooded merganser and the smew. At only 16 inches or 40 centimeters long, the smew is the smallest of the bunch.
Now, if you're looking at the silhouettes of mergansers, there's another feature they share. They have a crest formed by feathers. Both males and females of all species have some sort of crest sticking up from their heads. The only exception, more or less, is the male common merganser when he's in his breeding plumage. His glossy green head lacks a crest. But his girlfriend, the female common merganser, has a totally rad crest all year long.
It's shaggy and spiky. Her head, including the crest, is rusty brown instead of green. Female mergansers across the species have heads that are mostly reddish or brownish. But again, there's an exception. Female Brazilian mergansers look a lot like their male counterparts. Both sexes of that species have dark plumage overall, and they have iridescent green heads and necks.
They also both have crests, even though the male's is actually longer. As far as I know, Brazilian mergansers have similar plumage in all seasons. but during the non-breeding season, males of most other species look a lot like the females. The grand prize for the most outlandish, most in-your-face head ornament has to go to the hooded merganser. The male has a large fan-shaped white crest that has a thick black border. Its feathers are dense and smooth-looking, with no visible gaps.
If you look at him from the side, the male hoodie looks like he's got a massive, spherical head that's three sizes too large. But when you see him from the front or back, you realize it was all an illusion. The bird's head, or at least his skull, isn't oversized. The crest is thin and flattened from side to side, like a punk rocker mohawk.
The male hooded merganser can raise and lower his crest, sort of like a traditional paper fan. When the crest is lowered, it lays mostly flat and trails out from the back of the bird's head. In that position, the large patch of white on the crest is shaped more like a triangle or rectangle behind the eye. The crests of the other merganser species, by comparison, are kind of untidy and wiry-looking. Male mergansers in general have breeding plumages with high contrast.
Their bodies and wings have a lot of white, and their heads and necks are dark. Some, like the red-breasted merganser, also have patches of reddish-brown feathers. Another name for the red-breasted merganser that it's probably safe to assume no living person on Earth actually uses anymore is sea robin. Because, like the well-known European robin,
This merganser species has a patch of reddish feathers on its chest. The aptly named scaly-sided merganser has some cool-looking feathers on its flanks. Each of the large overlapping feathers is white, but also has several thin concentric black lines. The overall effect is beautiful, and it does look like fish or reptile scales. Now here's a quote for you. Few ducks are handsomer in life than a male American merganser. That bold and potentially controversial statement is from the book
A Natural History of North American Birds of Eastern and Central North America, first published in 1925. And by American merganser, they were talking about the common merganser. That quote, few ducks are handsomer in life than a male American merganser, is remarkably similar to the one that goes, few humans are handsomer in life than the male American podcaster, Ivan Philipson.
That quote is from my mom, so you can trust that it's completely unbiased and factually correct. But yeah, the male common merganser is a good-looking duck. The female, too, is pretty easy on the eyes with her shaggy ginger crest and blue-gray body. But returning to the hooded merganser, to me, that is the most beautiful, most handsomest of the mergansers.
The male is stunning. He's got that big crest, a black face and neck, and his eyes are bright yellow. Overall, his plumage is super high contrast and crisp looking. The back is black and the breast is white with two black stripes extending down the sides. His flanks are rufous or tawny with fine wavy patterns of gray and black, while the abdomen and undertale coverts are white.
Pickaxe Sheldrake. That's another old-timey name that probably no one uses anymore. It's an alternative name for the hooded merganser. Pickaxe Sheldrake. That's pretty rad, you gotta admit. I guess because the male's head looks sort of like a pickaxe, especially when he lowers his crest. And the word Sheldrake comes from Dutch and means a multicolored male duck. So you know what I'm thinking.
If I'm ever the front man for a punk rock band, that should be my stage name. Pickaxe Sheldrake. And of course, as a punk rocker named after a merganser, it would be mandatory that I have an epic white mohawk with a black border. Now, let us not forget our honorary merganser, the Smew, Mergelus albelus. It's the smallest of the six species, right? Well, the male Smew looks totally different from any other merganser.
He's mostly white with some bold black accents. There are circular patches of black around the eyes that some say make the Smew look like a cross between a duck and a giant panda. But when I look at a male SMU, I think it looks way more like the duck version of an Imperial Stormtrooper from Star Wars. These aren't the droids we're looking for. Seriously, it's uncanny how much the SMU looks like a Stormtrooper.
Look up some photos of the two side by side and you'll see what I'm talking about. Right. Now it's time to listen to the beautiful melodies of singing mergansers. Just kidding, these birds don't vocalize all that often. And the sounds they do make are not musical. Males make some calls during courtship when they're trying to impress females. and females sometimes respond during courtship with their own distinct calls. Both sexes make alarm calls, and these are mostly grunting sounds.
For example, the following recording is a common merganser making what I think is an alarm call. Next, we have some red-breasted mergansers recorded on the coast of Norway. It sounds like they're engaged in some courtship behaviors. The funny, sort of cat-like sound is the male. In response, you might hear the female making a few soft calls.
Now let's go over to the far northeastern part of China. There we have the scaly-sided merganser, mergus squamatus. In this recording, I'm pretty sure what we're hearing is a female calling to her chicks. She's making a low, repetitive grunting call. You can hear the high-pitched squeaks of the ducklings as well. The Brazilian merganser...
Mergus octocetaceus is the rarest merganser species in the world. So not surprisingly, there aren't all that many recordings of this species' vocalizations available. But I do have one for you, recorded in southeastern Brazil. A pair of Brazilian mergansers are making contact calls to each other. So far, we've been listening to the vocal sounds of merganser species in the genus mergus. Birds in that genus are what we sometimes call the true mergansers. Again, using air quotes.
But now we've got one more recording, and this one is from the hooded merganser, Lophidites cuculatus. So this is not one of the true mergansers because it's in its own genus. In this recording, we're listening to a group of hooded mergansers near the coast of Georgia in the U.S. It's January, and these ducks are making courtship displays.
The males produce a growling sort of call while making a display called the head throw or buck. The male arches his back and throws his head back so that his beak is pointing up. We're hearing several males making their growling calls in this recording. Alright, let's get into the geographic distributions of mergansers, their migration patterns, and their habitats. But first, you know I gotta geek out on the etymology of these bird names, on their origins.
Just in case I haven't made it clear already, the birds we're talking about today are ducks. They're all species in the duck and goose family, Anatidae. I covered that family in episode 18 of the podcast. But Mergansers and the SMU are different enough from other ducks that someone back in the day decided to give them their own name. And they're different enough that we're giving them their own podcast episode.
The word merganser originated with Latin, and it means diving goose or plunging goose. The bird that we call the common merganser goes by a different name in the UK and elsewhere in Europe. English-speaking folks over there call it the Goosander. So just remember that the common Merganser and the Goosander are the same species. Now, what about the name Smew?
That has to be one of the least flattering names for a duck. Smew. It sounds to me like what we call a sticky, mucus-like substance. Maybe because Smew sounds like a mashup. A portmanteau, if you will, of the words smear and glue. Smew. Anyway, for such a charming, beautiful bird, it doesn't have the best name. In my opinion.
It seems the origins of the name smeu are sort of murky. It might have come from a Dutch word meaning widgeon, which is another type of duck. Or smeu might have come from a German word meaning wild duck. In any case, the genus name for the SMU is mergelus. That's a diminutive form of the word mergus. So mergelus sort of means a cute little merganser.
And that, I would say, is spot on. The six species we're looking at today belong to a subgroup within the family Anatidae. It's a distinct evolutionary lineage called Mergani. That's spelled M-E-R-G-I-N-I. And I'm pretty sure it's pronounced Mergini. This group is usually called the Mergini tribe. Tribe is a taxonomic unit that's more inclusive than genus, but less inclusive than family or subfamily. Birds in the tribe mergani are often called sea ducks.
Other species in this group include the eiders, the scoters, the harlequin duck, the long-tailed duck, the golden eyes, and the buffalo head. Of all these sea ducks, The ones most closely related to our mergansers are the two golden-eye species and the buffalo head. Those are the three species that make up the genus Bucephala. The Smew, which is the only bird in the genus Mergelus, has sort of an intermediate position between Bucephala and Mergus.
For instance, the SMU's bill, with its hooked tip and serrated edges, is a feature shared with the Mergus mergansers. However, the SMU's proportionately small bill and steep forehead are more similar to what we see in those bucephala species.
Moving on, let's look at the distributions of mergansers on the map of the world. Where are these birds found? Most of them are restricted to the northern hemisphere. That includes the common merganser, aka the Goosander, as well as the red-breasted Merganser, scaly-sided Merganser, hooded Merganser, and the Smew.
The common and red-breasted mergansers have vast distributions that span northern North America and Eurasia. The red-breasted merganser breeds farther north than any of the other species. Some of its populations breed up in the Arctic. Maybe because of this far northern breeding distribution, the red-breasted merganser is one of the least studied ducks in North America.
As in, there's still a lot that ornithologists don't know about this bird. The hooded merganser is basically a North American bird. It's found all over the eastern half of the continent and in the far western states. The SMU is restricted to Europe and Asia. Most of its breeding populations are in northern Scandinavia and Russia.
The scaly-sided merganser is found only in East Asia, Russia, China, North and South Korea, and Japan. So those guys are all in the Northern Hemisphere. But in the Southern Hemisphere, we have the Brazilian merganser. in South America. But interestingly, there used to be at least a couple merganser species way down south in Australasia, in New Zealand to be more specific. But those species are sadly now extinct.
We'll talk more about them in a little bit. Some merganser species are migratory, at least partially. The common and red-breasted mergansers, for example, have some populations that are year-round residents while other populations migrate. The red-breasted merganser generally migrates farther than any of the other species. But the smew migrates pretty long distances as well. The scaly-sided merganser is also a migratory species. These birds breed in the Russian Far East and North Korea.
and then spend the winter mostly in China and Japan. The Brazilian merganser is a tropical species that does not migrate. In terms of habitat, these are all aquatic birds, of course. You find one merganser species or another in bodies of water like rivers, lakes, ponds, wetlands, bays, and lagoons. With only one exception, all merganser species make their nests in tree cavities.
so their habitat in the breeding season needs to include large, mature trees, and those trees are usually near water. Common mergansers prefer larger lakes and rivers in boreal and montane forests. Hooded mergansers, on the other hand, hang out in forested wetlands like swamps or beaver ponds with lots of trees around. The red-breasted merganser is the one species that doesn't use tree cavities for nesting.
So these birds are able to breed in far northern habitats like the tundra, where trees are pretty much non-existent. In the summer, red-breasted mergansers are usually found in freshwater or brackish wetlands not far from the ocean. The breeding habitat for the SMU is lakes, ponds, and slow-moving rivers in the boreal forests and bogs of northern Eurasia. Last but not least, Brazilian mergansers live year-round in clean, clear rivers flowing through tropical or subtropical forests.
Naturally, all mergansers need habitat that's teeming with lots of little fish and the other small aquatic creatures they feed on. Scientists have used a combination of fossil data and genetic data to study the evolutionary histories of mergansers. Fortunately for us, there was an important study about these birds published just a few months ago in the Zoological Journal of the Linnaean Society.
A group of researchers based in New Zealand and Australia used genetic data from mergansers to figure out the evolutionary relationships among all the species. Those relationships tell us something about when and where the species evolved. So a lot of what I'll be talking about regarding the evolution of mergansers comes from this 2024 study. The lifestyle of pursuit diving, that is chasing fish around underwater, seems to have evolved just once in the duck family.
So once upon a time, there was a species that transitioned from being more of a grazing diver to a streamlined, fast-swimming, fish-chasing duck. That species was the common ancestor of the six species we're talking about today. It lived roughly 20 million years ago, somewhere in the northern hemisphere.
It was most likely a migratory bird that nested in tree cavities. So that was the origin of the Merganser lineage. Then, the first to peel off and go its separate way, in the evolutionary sense, was the Smew. So it's the most ancient, most divergent species of the six. Again, the SMU is the only species in the genus Mergelus. The genus Lophidites, that of the hooded merganser, diverged from the rest of the ancestral merganser lineage around 18 million years ago.
Between 11 and 9 million years ago, the remaining lineage diversified to give us all the species in the genus Mergus. This recent genetic study also gives us some insight into how and when some mergansers ended up in the southern hemisphere. The researchers in the study were able to sequence mitochondrial DNA from museum specimens of the Brazilian merganser and an extinct species from New Zealand called the Auckland Island merganser.
That DNA sequence data was then compared with data from the other living merganser species, as well as a bunch of other sea ducks in the mergani tribe. This research suggests there were two independent colonization events, occurring at least 7 million years ago. The Auckland Island merganser is most closely related to the common merganser.
So that tells us there was a colonization event where some common mergansers ended up in the New Zealand region, and the population they founded eventually evolved into a new species on the Auckland Islands. The origin of the other southern hemisphere species, the Brazilian merganser, is quite different. That bird's closest living relative is the scaly-sided merganser, which you might recall lives in the far east of Asia.
Earlier, I mentioned that the Brazilian merganser, mergus octocetaceus, is the rarest of the six species. Well, that species is actually one of the most threatened waterfowl species in the world. It's critically endangered. According to BirdLife International, there are less than 250 of these birds left on the planet. If you're trying to picture a Brazilian merganser, it's a dusky gray-brown all over with a shiny green head and neck. And it's got a ragged crest hanging off the back of its head.
This duck used to be more widespread in South America, but today it survives in only a scattered collection of small populations, mostly in Brazil. A variety of human-related factors are driving Brazilian mergansers towards extinction. These include dam construction, which obliterates river habitats, and deforestation. Another big threat is pollution from sewage, mining, and agriculture. Similar threats are faced by other merganser species around the world. These birds need clean water.
in rivers, lakes, ponds, and coastal waters that are rich with healthy fish populations. Dams, deforestation, and pollution can all be devastating to mergansers. The scaly-sided merganser is also in trouble. It's listed as endangered at the global level. The estimate is that there are fewer than 5,000 of these birds remaining in East Asia.
Scaly-sided mergansers are suffering from habitat loss because of logging. People also hunt them illegally, trap them accidentally in fishing nets, disturb them with obnoxious motorboats, and so on. If we're not careful, we could lose these threatened merganser species forever. Humans already have a track record of killing off some merganser species. One of them was the aforementioned Auckland Island merganser.
This species was still living on the Auckland Islands archipelago, south of mainland New Zealand, until the early 1900s. This species was killed off by hunting and by the ravages of introduced predators like cats and rats. There are still some museum specimens of the Auckland Island merganser, so we not only have DNA from this species, we also kind of know what it looked like. It was about the size of a red-breasted merganser.
The male was pretty dark overall, with brown and blue-gray plumage. His head and neck were a dark reddish-brown, and he also sported a short, shaggy crest. There was another species, the Chatham Island merganser, that was possibly a close relative of the Auckland Island merganser. Several thousand years ago, humans appeared to have driven the Chatham Island merganser to extinction.
We know about this species, whose scientific name is Murgus millinarii, only from a few fossils. It lived only in the Chatham Islands, which lie east of mainland New Zealand. This bird was smaller than any of the other merganser species we're talking about today. At this point in the episode, we all understand that mergansers are fish eaters. They're specialized ducks honed by natural selection to be fish chasing machines.
Like cormorants, loons, and grebes, mergansers are pursuit divers. Specifically, they're pursuit divers that propel themselves underwater with their feet. Some other kinds of pursuit divers... like puffins and penguins, use their wings for propulsion underwater. Let's take a few moments to talk some more about the diet and foraging strategies of mergansers.
The common merganser, the gusander, is perhaps the most familiar species for many of us. It eats mostly fish. Studies that have quantified the proportion of fish in the common merganser's diet have found that it's somewhere between 50 and 90 percent. At least 50 fish species have been recorded in this bird's diet. The primary prey species include salmon, trout, suckers, sculpin, shad, sticklebacks, chub, and minnows.
The specific types of fish eaten by common mergansers vary depending on habitat, geographic location, and time of year. But the fish are generally small. typically 4 to 12 inches long, which is 10 to 30 centimeters. I just mentioned that trout and salmon are on the menu for these mergansers. Some people think that because they feast on young salmon,
the birds can negatively impact salmon fisheries. You might recall that I talked about a similar conflict between humans and cormorants in episode 99. And like cormorants, mergansers have sometimes been persecuted and killed because of their supposed negative effect on fish populations. While predation by common mergansers on salmon is a thing,
The actual extent of their impact on salmon fisheries is mostly unknown. It's still up for debate. Variation across different ecosystems makes it difficult for scientists to generalize their findings. It seems that, yes, in some river systems, mergansers might play a role in limiting juvenile salmon populations, at least at a local level.
Meanwhile, in many other rivers, their impact is probably minimal compared to other environmental stressors. You know, stressors like dams, pollution and overfishing by humans. In any case, it sounds like more research is needed on the question of how mergansers affect commercial salmon fisheries. Anyway, that's fish. The rest of the common merganser's diet is made up of invertebrates and amphibians. We're talking about critters like caddisfly and mayfly larvae, crayfish, and worms.
The hooded merganser also eats lots of fish, which make up roughly 45-80% of its diet. But compared to many of the other merganser species, hoodies focus a bit more of their attention on aquatic invertebrates. They're especially fond of crayfish. Something like 20-50% of a hooded merganser's diet can be composed of crayfish and other freshwater crustaceans.
All merganser species use their muscular gizzards to grind up the bones and exoskeletons of their prey, often with some gravel in the mix to help with the grinding. But apparently the hooded merganser has an extra thick, extra strong gizzard, which is probably useful for processing all those crunchy crayfish. Mergansers of all kinds use their eyesight underwater to locate fish and other prey. Their eyes are well adapted to see underwater.
with the ability to dramatically alter their focus by changing the shape of the lens in the eye as they move from air to water. One common foraging technique is snorkeling. A merganser paddles around on the water's surface with its face down in the water. It scans for the movement of prey below. The third eyelid, the nictitating membrane, is transparent.
This membrane covers the eye underwater, protecting the eye while still allowing the bird to see, like swim goggles. Mergansers go on the hunt in other ways, too. They make shallow dives or deep dives, visually searching for prey out in the open. Or a merganser will poke around with its beak in holes and spaces between rocks on the bottom.
This will sometimes spook a fish into revealing itself. And then the high-speed chase is on. And it takes a lot of little fish or invertebrates to fuel the energetic lifestyle and high metabolism of a merganser. A red-breasted merganser, for example, needs to eat about 15 to 20 fish a day. To meet that quota, the bird might have to dive up to 300 times over the course of four to five hours.
Another interesting foraging technique used by some mergansers is cooperative herding. No, not herding sheep or cats, but fish. Of course. This is a behavior seen in red-breasted and common mergansars. And maybe some of the other species do it as well. I'll read you an excerpt about this behavior from an observation published in 1965 in the journal The Auk. This observation was made in a bay on the west coast of Mexico. Quote,
We saw seven red-breasted mergansers behaving in a manner that suggested they were fishing cooperatively. The seven birds were feeding in a shallow arm of the bay in water less than 24 inches deep on an incoming tide. They swam in a loose line, moving slowly, more or less in the same direction, with their faces either under the surface or above it for short periods of preening.
When a hunting bird discovered a fish it immediately gave chase, flapping its wings and running on the surface. The positions of the fish were apparently determined by the birds peering under the water at frequent intervals. As soon as one bird began a chase, the others joined in the pursuit, the nearby birds flapping and running along the surface, those more distant flying.
In the few seconds it took the last bird to arrive, a semicircle was formed by the birds with the pursued fish in the center of the ark. As the birds chased the fish one or another of them dived under the surface in pursuit surfacing at about the time the others reached that spot. This diving continued in each case until one of the birds caught the fish.
immediately upon surfacing that bird would eat the fish as soon as a fish was caught the rest of the birds would begin to disperse and to hunt again occasionally in the course of a chase one or two of the trailing birds would be distracted by the discovery of another fish which they then chased the secondary pursuits did not seem to be very successful
We saw no fish caught under these circumstances, while the cooperating group captured at least 10 fish in 15 minutes. End quote. I would love to see this behavior in person. But I found a short video that shows a mixed flock of both red-breasted and common mergansers cooperatively herding fish in British Columbia, Canada. I'll put a link to the video in the show notes.
Over in Europe, smeu form large flocks in winter, sometimes with thousands of birds. Groups of them will often dive in unison. So perhaps this species engages in a little cooperative fish herding as well. Other types of birds take advantage of how mergansers push fish closer to the water's surface during cooperative herding. Birds like snowy egrets, bonaparte's gulls, and ring-billed gulls mill around at the water's surface, waiting for their chance to grab fish that mergansers scare up.
Or these non-merganser birds will just try to steal any fish that a merganser catches. Even bald eagles are guilty of this disgraceful thievery. But taking advantage of other birds can go both ways. Mergansers will keep their eyes peeled for flocks of gulls that are making a ruckus where the gulls have discovered a big school of fish. The mergansers then swim or fly over to get a piece of the action.
This is kind of like me when I'm out walking aimlessly at a city park and I happen to notice some people gathered at a company picnic or a kid's birthday party. I slide over nonchalantly to the picnic table with all the potato salad, cookies, chips, and whatnot. And I can usually get my own piece of the action, at least a few handfuls crammed in my mouth, before someone sees me and realizes I'm an imposter. I run away before the cops show up.
just like a merganser paddling furiously across the surface of a river. When it comes to their breeding system, mergansers are generally monogamous. But males of most species abandon the females after the females begin incubation. And it's unknown how common it is for pairs to reunite in subsequent years. Male Brazilian mergansers stick around, however. The male in that species protects the incubating female and then the hatchlings. The whole family stays together for months.
Generally speaking, there's a fair amount of elaborate courtship behavior in these mergansers when they first pair up, early in the breeding season. Males make courtship displays, and to a lesser extent, so do females. These behaviors involve various forms of neck stretching, head shaking and head throwing, crest raising and wing flapping. Male hooded mergansers have one of the most elaborate courtship displays. They raise and fan out their impressive crests and shake them.
During the head throw display, a male makes that low frog-like or growling call we heard earlier. I'll put a link to a video of hooded merganser courtship displays in the show notes, so you can see these behaviors in action. They're pretty impressive and also pretty funny. Some merganser species, like the common and hooded, do something called ritualized drinking during courtship. Now, you might be thinking,
Yeah, ritualized drinking, like St. Patrick's Day, or at frat parties with the red solo cups and beer pong. But with mergansers, ritualized drinking, also called ceremonial drinking, doesn't involve alcohol. It's a behavior where the birds greet each other. They dip their beaks and go through the motions of taking a sip of water from the surface of the lake or pond or whatever. Both males and females do this.
Sometimes they do ritualized drinking just before mating, but it can also be used in other kinds of social interactions. For example, when new individuals join the flock. Interactions among mergansers aren't always about mating or about friendly greetings. Some species are highly territorial. This is true for the Brazilian and scaly-sided mergansers.
which, as you might remember, are each other's closest relatives. Breeding pairs of Brazilian mergansers defend a year-round territory on a river or stream. And their territory can be pretty extensive. up to 7 miles or 12 kilometers long. But it seems the other species are not so territorial.
However, males can still be aggressive toward other birds that get too close to their mates or their nest sites. As we touched on earlier, in almost all merganser species, the nest site is a cavity in a tree. For example, the common merganser often uses a hole originally carved out of a tree by a pileated woodpecker. Or in Europe, the holes are often excavated by black woodpeckers.
The height of the cavity can be up to about 100 feet off the ground, which is 30 meters. Less frequently, common mergansers will make their nests in rock crevices, in dense vegetation on the ground. burrows in soil, or in old buildings. Several merganser species will happily use artificial nest boxes. That goes for the common and hooded mergansers and the smew.
Only the red-breasted merganser nests exclusively on the ground. These birds make sure their nests are well concealed and protected from the elements. So they place the nest in dense bushes, under driftwood on the beach, between boulders, etc. Apparently, there was even a case in the Arctic where some cheeky, red-breasted mergansers build their nest in an abandoned igloo. And that is just fantastic.
Once the nest is ready, it's time to fill it with some eggs. Depending on the species, a typical clutch ranges from 8 to 13 eggs. But if you were to peek inside the nest of a common red-breasted or hooded merganser, it wouldn't be unusual to find a couple dozen creamy white eggs in there. So what's going on here?
Well, these mergansers have no shame in acting as brood parasites, taking advantage of their own kind. When a female hooded merganser, let's say, lays some eggs in the nest of another hooded merganser, That's called intraspecific brood parasitism. So that nest with a couple dozen eggs contains not just the eggs of the female who occupies the nest,
but also some eggs from one or more of her neighbors. They snuck in and dropped eggs when the nest owner wasn't looking. And sometimes the parasitic birds are ducks of other species. other merganser species, or even wood ducks or golden eyes. In the latter case, when the eggs in a nest are from more than one species, we call that inter-specific brood parasitism.
You know, like what cuckoos do. I did a podcast episode all about that. Anyway, only the female incubates the eggs and takes care of the ducklings. Because Dad is a deadbeat. He took off already. Actually, it's probably not fair to call the males deadbeats, because their behavior of leaving when incubation begins might actually have some adaptive advantages, not just for himself, but for everyone in the family.
For example, by leaving the nesting area, males might reduce the chances of attracting predators to the vulnerable nest and female. Because males are way more conspicuous, right? In any case, mom incubates the eggs, and then eventually, here come the ducklings. To the surprise of absolutely no one, baby mergansers are insanely cute. They're precocial.
which means as soon as they hatch, they're covered in fuzzy down feathers, and their eyes are open, and they're able to move around on their own. After hatching, the entire family abandons the nest within about 24 hours. When the nest is in a tree cavity, this exodus is one of the most astonishing and most adorable spectacles in nature. The chicks are able to climb up in the inside of the tree cavity to reach the entrance hole.
They have long claws on their toes and stiff tail feathers to brace themselves against the wood as they climb. They clamber towards the light at the end of the tunnel. Meanwhile, mom is down on the forest floor, calling to her babies, encouraging them to leap out of the nest. Remember, the nest can be really high off the ground, so it's no small feat for the baby ducks to make this jump.
but each of them eventually does. For a few glorious moments, the sky is raining little fuzzballs. Each chick spreads its tiny wings and webbed feet in an effort to slow the fall. The chick weighs almost nothing, luckily, so it hits the forest floor and bounces once or twice without any harm. Sometimes the impact is also cushioned by a layer of fallen leaves or moss.
There's a great PBS video showing some baby hooded mergansers jumping out of a tree. I'll put a link to it in the show notes. It's hilarious. Once the Merganser family is all together on the ground, mom leads the way to the water. They might have to trek for a mile or so before they reach a river or a lake. The babies stay close to mom in the water.
She's got a little entourage of fuzzy ducklings trailing out behind her as she swims. But there are usually a few of the little buggers riding high and dry on the mother's back. looking smug and making fun of all those losers who have to swim. The female's primary job is to protect her brood, since the youngsters can feed themselves. Their early diet is mostly aquatic insects and other invertebrates. They eat caddisflies, mayflies, backswimmers, flies, water striders, and maybe a few seeds.
Then, in most merganser species, the ducklings switch to eating mostly fish. In the common merganser, for example, they start eating fish when they're about 12 days old. Sometimes you come across a female common merganser or red-breasted merganser and she's got like 40 or more ducklings in tow. It's crazy. It could be that this is the result of that intraspecific brood parasitism we were talking about earlier. But there's another phenomenon that leads to this situation.
It's called creche formation, or brood amalgamation. Creche is spelled C-R-E-C-H-E. At least with ducks like mergansers... Kresch refers to a group of young ducklings that are cared for collectively by one or more adult females, not necessarily their biological mother. A few years ago, there was a female common merganser in Minnesota who made the headlines when she was photographed with over 50 ducklings swimming in a line close behind her. It was ridiculous.
There are probably multiple factors that lead to creche formation like this. One might be that some ducklings get confused and start following the wrong mom when two different broods cross paths on the water. By the time a female realizes she's got a few extra babies trailing behind her, it's... Too late, or if she ever realizes it. In any case, the other female is long gone. Maybe this is like accidentally picking up the wrong luggage at the airport because it looks just like yours.
Sort of like all those standard black suitcases on the luggage carousel, every baby merganser looks pretty much identical. The amount of time a female stays with her chicks varies. If she can dump them off into the care of another female, a mother might abandon her chicks after just a week or two. Otherwise, the family will most likely stick together for some months.
In the Brazilian merganser, where both mom and dad help to protect the ducklings, the family may stay together for up to 10 months. Some female mergansers may return year after year to use the same nest cavity, and they may tend to breed not far from where they were born. For example, a study in Finland... found that 127 out of 156 banded breeding female common mergansers were recaptured at the study site in subsequent years.
This suggests a high degree of breeding philopatry in females. Philopatry is spelled P-H-I-L-O-P-A-T-R-Y. This is the tendency of a bird or other animal to return to or stay in the place where it was born, especially for breeding. Another study, using genetic data from DNA, also showed evidence of high levels of female philopatry in common mergansers, this time in North America.
And there's also some evidence of this behavior in red-breasted mergansers. In terms of lifespan, mergansers have been recorded living up to 13 or 14 years in some species. But those are the extremes. A typical merganser in the wild probably has a significantly shorter life expectancy. As they try to survive from one day to the next... Mergansers must face the elements and the many threats imposed by humans. And of course, there are predators.
Nest predators like squirrels, snakes, and raccoons eat eggs and chicks if they can reach the inside of the nest cavity. Adult mergansers have many potential predators, both avian and mammalian. Birds of prey like deer falcons, snowy owls, and bald eagles will eat common and red-breasted mergansers. The Brazilian merganser can fall victim to raptors like great black hawks and the black and white hawk eagle. And an example that seems kind of wild to me...
There is apparently documentation of killer whales, orcas, eating common mergansers. Can you imagine seeing that? A merganser is bobbing around on the surface of the ocean, minding its own business. And then suddenly this enormous black and white sea monster shoots up from the deep to swallow the bird whole. Yikes! The ocean is spooky, you guys.
And that is all I have for you today regarding the world's six wonderful merganser species. Four in the genus Mergus, one the hooded merganser in the genus Lophidites, and the smew in the genus Mergelus. I hope you've enjoyed learning a few things about these saw-billed, pursuit-diving, ritualized-drinking torpedo ducks. That's a wrap on episode 105. If you want to learn about the entire duck family, remember to check out episode 18 of the podcast.
I'd like to welcome the most recent recruits to my Patreon community. And a site, Jamie Cuaruccio, Taylor Mon, Peter D., and Joshua Atchley. Thanks so, so much for becoming supporters of the show. And a big thank you to my entire Patreon community for making all of this possible. If you are thinking about becoming a supporter, you can check out my Patreon page over at patreon.com slash scienceofbirds. There's also a support the show link in the show notes.
And if you have some words you'd like to share with me, please go ahead and shoot me an email. Perhaps you'd like to offer a better common name for the SMU. You kind of can't go wrong since just about anything would be an improvement over SMU. I'm gonna go with Stormtrooper Duck. Anyway, my email address is ivan at scienceofbirds.com. It sometimes takes me a week or more to respond, but I try to get back to everyone who writes to me.
You can check out the show notes for today's episode, along with some curated photos of mergansers, on the Science of Birds website, scienceofbirds.com. This is Ivan Philipson. Thanks for listening, and I'll catch you next time. Cheers.