Do seahorses validate “queerness”? The naturalistic fallacy committed by the Sussex Wildlife Trust

January 21, 2022 • 11:15 am

Every day I get six or seven links from readers about the infestation of society by performative brands of DEI (i.e., “wokeness”). The links are often distressing and depressing, but I have to tell readers “I’m sorry, but I can’t write about everything!”

But when I am compelled by the laws of physics to write about something is when people try to bend biology to fit their ideological narrative. The most egregious example of this is the claim that there is no such thing as a sexual binary in humans and other animals, which is just wrong. Males have small mobile gametes (that’s the definition), and females big and immobile ones. Just like my Drosophila, about 99.99% of humans are either male or female by this definition. Hermaphrodites or other intermediates are not “other sexes”; they are developmental anomalies. (That’s not a slur on human intermediates; it’s a statement that you get the very rare intermediates only when development slips off the rails that have evolved to ensure a sexual binary.)

These attempts to refer to nature as a way of validating human behavior, morality, or ideology is, of course, an example of the “naturalistic fallacy,” usually described as the fallacy of saying “what’s seen in nature is good in humans.” And it’s a dumb fallacy, because a lot of animals behave in nature in ways that we would consider immoral in our own species. (Chimps, for example, attack other bands of chimps and rip individuals apart while they’re still alive. Some spider females kill and eat males after mating.) We can’t look to nature for morality, because, at bottom, nature is amoral, for animals don’t have the capacity to argue and make considered judgments about how to behave. Often “considerate” behavior towards others is the evolutionary product of reciprocal altruism or kin selection.

So when the Sussex Wildlife Trust tries to use the pregnancy of male seahorses as a justification for “queerness”, as they do below, they’re committing the naturalistic fallacy. The reason we shouldn’t discriminate against non-cis people is because discrimination is wrong and hurtful, not because male seahorses (and, by the way, male pipefish and sea dragons, contra the tweet below) get pregnant. Mallard drakes sometimes kill females during forced copulation, which in humans is the equivalent of rape. Does that make rape okay? You get my point.

Here’s the tweet. The original has been deleted (I wonder why?) but here’s a screenshot of the original:


Now a bit of biology before we go on to the associated article.  Seahorses have a fascinating mating and breeding system. They’ve evolved so that the males largely take care of the eggs. (In many species, males do at least half the tending and rearing). In seahorses, pipefish, and sea dragons, this occurs by males sequestering the eggs in their kangeroo-like pouches, fertilizing them there, and sequestering them until hatching.  (This may be a way to increase offspring number by favoring those individuals who protect their reproductive investment by protecting fertilized eggs.)

The important thing is that, in seahorses, sea dragons, and pipefish, the females produce eggs faster than the males can put them in their pouches, so females are always looking around for an “empty” male. Because—unlike in most animals—females are thus competing for males’ attention, and sexual selection is reversed. It’s the opposite of what happens in most other species, in which males compete to fertilize females. This is why, if there is sexual dimorphism in seahorses, it’s the females who are more elaborately decorated and with more secondary sexual characteristics. (See also here.)

Note that the males, while they take care of fertilized eggs and in that sense are pregnant, are still males, as they produce sperm rather than eggs. So you could say that “males get pregnant”, but that’s not the same thing as transsexual men who can sometimes get pregnant, nor does seahorse pregnancy somehow show that transmale pregnancy is “okay” or “moral”. It IS perfectly okay, but not because you find it in some marine species.

I like to show students the video below of a male seahorse giving birth, which looks almost as laborious and painful as labor in human females. This form of reproduction, given the female’s rapid rate of producing eggs, may have evolved to protect eggs and embryos from predation. We just don’t know.

What we do know is that males have a form of pregnancy, but this says nothing one way or the other about transsexual pregnancy in humans. The pregnant seahorses are neither queer nor transsexual, but males, and there’s no morality in the fishes (yes, seahorses, sea dragons, and pipefish are “fish”).

I wouldn’t have written all this if reader Al, who was steamed, sent me this associated link from the Sussex Wildlife Trust news (click on screenshot to read).  Now I’m not going to go after this very hard, as I want to just reiterate the naturalistic fallacy and how it’s used as a justification or valorization of human behavior. And yes, pregnant seahorses do show that animal behavior is diverse and unexpected.  But pregnant male seahorses remain males, and they’re not “queer,” either, as the author seems to imply in her piece.

But the seahorses are used to somehow buttress the insecurity of a woman trying to come out as queer.

A few quotes:

As a keen zoology undergraduate who adored, almost worshipped, Darwin’s theory of evolution, I couldn’t quite come to terms with his theory of sexual selection. It really didn’t add up as I was tentatively stepping out of the queer closet back in 1996. I lived and breathed evolutionary theory but where did I fit in? A deviation? An anomaly? A kink in the genetic spiral of life? So, of course, I started studying the evolution of sex and soon discovered how incredibly diverse and fascinating the plant and animal kingdoms (more like queendoms or even queerdoms) really are in terms of gender and sexuality.

. . . .In the plant world too there is a whole host of queerness to explore. In fact bisexual flowers are described as “perfect”, having both male and female reproductive structures. Examples include roses and lilies but also the horse chestnut, highlighted in a wonderful project by the Queer Botany Society at the Walthamstow Marshes SSSI.

Now, with my work for the Sussex Kelp Restoration Project much of my favourite flagship “queer” marine species are linked directly to our conservation work here on the Sussex Coast. For example bottlenose dolphins who are known to engage in homosexual behaviour and sex for fun, again thought to increase social bonding and cooperation. The black seabream which are all born female and change to male at maturity (known as protogynous hermaphrodites). And finally the incredible seahorse species that in my opinion can claim the throne of the animal drag-kingdom in having the only true reversed pregnancy.

I’m sure Darwin would agree that rather than it all being about nature versus nurture we should focus more on nurturing our true nature, that part of us that is wild and free and far from binary. Wouldn’t it be dull if everything were so very black and white… life and love is in fact gloriously technicolour thanks to evolution’s rainbow.

Now people can find solace where they will, but I think it’s misguided to look to nature to validate a behavior in humans. For every mammalian species that shows homosexual behavior, there are a dozen who don’t.  (Do those show that homosexuality is “unnatural, ergo wrong?” Of course not!) And homosexuality in humans, which often involves attraction solely to members of your own sex, is not at all the same thing as homosexual behavior in dolphins. For when a the male wants offspring, he knows where to go. Should a rapist find validation by studying ducks?

The last sentence of the piece above, referring to “evolution’s rainbow,” is likely a reference to Joan Roughgarden’s Evolution’s Rainbow, a book-length attempt to justify human non-cis-ness by looking at animals (Roughgarden is a transsexual female). I reviewed it for the Times Literary Supplement in 2004. My review is no longer online but I have a copy and will send it to those who want to read it. Here’s the last part of my review (it was mixed: I found Roughgarden’s descriptions of behavior being very good but her moral “lessons” untenable). Yet the warning about the naturalistic fallacy is apparently is as relevant today as it was when I wrote this 18 years ago:

But regardless of the truth of Darwin’s theory, should we consult nature to determine which of our behaviours are to be considered normal or moral? Homosexuality may indeed occur in species other than our own, but so do infanticide, robbery and extra-pair copulation.  If the gay cause is somehow boosted by parallels from nature, then so are the causes of child-killers, thieves and adulterers. And given the cultural milieu in which human sexuality and gender are expressed, how closely can we compare ourselves to other species? In what sense does a fish who changes sex resemble a transgendered person? The fish presumably experiences neither distressing feelings about inhabiting the wrong body, nor ostracism by other fish. In some baboons, the only males who show homosexual behaviour are those denied access to females by more dominant males. How can this possibly be equated to human homosexuality?

The step from “natural” to “ethical” is even riskier. As the philosopher G. E. Moore argued, identifying what is good or right by using any natural property is committing the “naturalistic fallacy”: there is no valid way to deduce “ought” from “is”. If no animals showed homosexual behaviour, would discrimination against gay humans be more justified? Certainly not. Roughgarden’s philosophical strategy is as problematic as her biological one.

Roughgarden believes that evolutionary biologists, with their enthusiasm for the “classical” gender roles of the neo-Darwinian theory of sexual selection, are partly responsible for society’s unease with gay and transgendered people. She is wrong. This theory is powerful and largely correct. Yes, there are nuances of behaviour that require special explanation, or that we don’t yet understand. But nobody, least of all Darwin, ever claimed that evolutionary biology is characterized by ironclad laws. Our field is not physics. Nevertheless, some generalizations, such as the pervasive competition of males for females, can be powerful and useful.

Yet in the end, all of this is irrelevant to the gay and transgendered community’s genuine concerns about repressive social attitudes. Rather than wringing her hands about the theories embraced by her biological colleagues, Joan Roughgarden might consider visiting a school board meeting deep in the American Bible Belt. There, ironically, she would find where opposition to a sexually diverse society really thrives, as does opposition to the very theory she is partly lambasting, Darwinism. It is not the intellectuals who are the problem; it’s the anti-intellectuals.

Nature, as varied as it is, can be used to “validate” any human behavior, therefore it can validate NO human behaviors.

Two baby tigers are born!

January 19, 2022 • 1:45 pm

It’s time for some relaxation. Tomorrow is Go for a Walk Day but I’m going to do this now. But I want you to see this video of a mother tiger (I don’t know the zoo or sanctuary) giving birth to two babies. It all turns out okay, but there’s a bit of suspense. At any rate, you get to see baby tigers being born!

It’s fascinating that a mother tiger who’s never had cubs knows exactly what to do: open the amniotic sack and lick the hell out of the baby to get it to start breathing. Those behaviors are surely encoded in the DNA, for of course any mother who didn’t do those things wouldn’t leave viable cubs. But I digress . . .. . watch two birthdays.

Oh, be sure to listen for the cries of the newborns.

Shrews do the conga

December 30, 2021 • 2:15 pm

Bruce Lyon brought this short video to my attention. How does a nocturnal mammal get about with her young?

The video asks why they do this? Well, it’s clear that it keeps the family together, and here’s one explanation:

Shrews are highly territorial animals and only socialise with one another in the mating season. Females have three or four litters of 5-7 young between May and September. Females are promiscuous and a litter may have two or three different fathers. Young shrews are occasionally observed following their mother in a ‘caravan’. Each shrew grasps the base of the tail of the preceding shrew so that the mother runs along with a line of young trailing behind. This behaviour is often associated with disturbance of the nest and may also be used to encourage the young to explore their environment.

How much exploring can you do when your nose is up your sister’s butt? Can you think of any other reasons?

Here’s a daytime conga:

Animals vs. GoPro cameras

December 28, 2021 • 1:15 pm

Here’s a 5-minute video, made by GoPro, showing the top ten animals that have interacted with their cameras.

The video snippets, and I’ve put the links to the whole original videos as well, as you’ll want to watch some of them, especially the LION HUG.

00:00 Intro
00:16  #10 – Great White Shark Encounter (LINK)
00:55  #9 – Owl Dance Off (LINK)
01:11  #8 – Squirrel Fail (LINK)
01:31  #7 – Snow Leopard Meets MAX (LINK)
01:57 #6 – Lion Mouth Cam (LINK)
02:27  #5 – Surfing with Dolphins (LINK)
02:53  #4 – Orca vs. Paddle Board (LINK)
03:15  #3 – Gorilla Tickling (LINK)
03:48 #2 – Scuba Dive with 1 Million Fish (LINK)
04:15  #1 – Lion Hug (LINK)

Happy Thanksgiving!

November 25, 2021 • 2:01 pm

Let’s not forget our animal friends on this day of gluttony. Reader J. C. McLoughlin didn’t, and sent these two photos with a caption:

I append views from the kitchen window of some of the ravens who visit our corvid-table, which this Thanksgiving morning sports a fryer chicken in a wire gibbet. The chicken will be gone by this afternoon.

Man, these ravens are going to FEAST!

Small spider pulls big empty shell up into a bush to make itself a home, and I haz questions

November 24, 2021 • 1:30 pm

This is one of the most amazing pieces of spider behavior I’ve ever seen (filmed, of course, by the BBC and narrated by Attenborough). You have to watch yourself it as it’s too complex to describe.

There are several questions that arise, and I have no answers:

a.) Does every member of the spider species do this, or is this a behavior evinced by just one individual? (Nobody knows.)

b.) If the latter, how the hell did that spider figure out what to do? If it’s not species-wide, it probably isn’t genetically encoded in the brain, and this behavior would have to be figured out! I don’t think that spiders have that kind of savvy, though they can spin very intricate webs or build trapdoors. Those however, are species-wide evolutionarily derived behaviors.

c.) How does the process of affixing one strand after another to the shell lift it up? The spider isn’t strong enough to haul the shell up, nor does it seem to be using the silk as a pulley, which wouldn’t work anyway

If readers can answer any of these questions, be my guest!

Happy Thanksgiving to all. I’m taking a tiny break tomorrow, so although there will be posts, don’t expect many. Enjoy your noms instead!

h/t: Jim

Readers’ wildlife photos

November 8, 2021 • 8:00 am

Today we have a combination science-and-photo post from Bruce Lyon, an ecologist, ornithologist, and evolutionary biologist at the University of California at Santa Cruz (unless you’re new, you’ll have seen his posts before). Today is WEASEL DAY!

Drop goes the weasel

I have some long-tailed weasel (Neogale frenata) photos to share—mostly just photos but I will bring in a bit of science. This species is related to the stoat (Mustela erminea), also known as ermine or, in North America, as the short-tailed weasel. I mention this because a few weeks ago Jerry mentioned that he is very fond of stoats. However, when I Googled to search for stout, the top links were all to the famous dark strong beer so maybe that was what our host was about! [JAC: Bruce misspelled “stoat” as “stout”; I’ve corrected all but one usage,.]

Today the focus is on the mammal, not the malted beverage.

I regularly encounter weasels while watching birds on the coast between Santa Cruz and San Francisco in Central California. They are common on the coastal bluffs and seem to use the same dirt tracks that I hike on so I see them fairly often. They are typically shy and give only fleeting views before darting into the vegetation once spotted, but occasionally they do stay in view long enough to pose for a few photographs.

Below: A typical fleeting view, in this case the north end view of a southbound weasel. Zooming in on the photo shows that this animal has a big package below his tail—testicles—so it was a male.

Many of the readers are likely familiar with the phrase “pop goes the weasel“, which originated in England in the 1800’s as a song and then a dance. The specific meaning of the phrase ‘pop goes the weasel’ is not clear. I recently had a couple of encounters with a variant of the phrase— ‘drop goes the weasel’. Last spring while birding the coastal bluffs a weasel came bounding towards me along the dirt track we were sharing, and it had prey in its mouth. I expected the prey to be a rodent. When the weasel saw me it dropped the prey item on the track and darted into the bushes. After a minute it came back and grabbed the prey item and my photos showed it to be a rubber boa (Charina bottae), the first time I have ever seen this interesting snake.

A few weeks later something similar happened at the same spot. I had been watching birds and not paying attention to the track (or looking for weasels) but at one point I looked down and saw a fresh-looking dead rodent on the track (which I suspect was a vole). When I checked the vole it was warm and very fresh (not in rigor mortis). Figuring it might be another case of drop goes the weasel, I moved back and barely had time to focus my camera before the weasel popped out of the bushes, grabbed the rodent and darted back into cover.

Below. Weasels are ferocious and can take prey much larger than themselves. Here is video, from the Attenborough series Life, of a stoat chasing and eventually killing a rabbit many times its size. 

Below: Weasels are very long and skinny which allows them to explore narrow underground burrows for prey like rodents. Here a weasel surveys its surroundings, looking like a periscope.

Below: Same animal

Below: a very colorful individual. Note the orange chest and belly and the conspicuous face markings. What a gorgeous mammal!

Below: a closeup of the same animal showing the conspicuous face markings.

When I see such colorful striking markings in birds, I wonder if there might be a signaling aspect and I wondered if this color might be a signal in the weasels. Weasels are such fierce bad-asses for their size that I wondered if these markings might be a form of aposomatic coloration— coloration that warns predators not to mess with the animal. Aposomatic coloration is common in nature: familiar examples include bees, monarch butterflies and coral snakes.

I found a study that proposed this same idea—that the conspicuous facial patterns in mid-sized mustelids may be a warning signal to would be predators to steer clear of these ferocious animals (Mustelidea is the taxonomic family that includes weasels ): Newman, C., C. D. Buesching, and J. O. Wolff. “The function of facial masks in “midguild” carnivores.” Oikos 108.3 (2005): 623-633. From the paper’s summary the authors state A group of medium sized carnivores possesses conspicuously colored facial markings or masks. This facial coloration is most compatible with the aposematic warning hypothesis and functions to deter predation by larger carnivores.

Below: a figure 1 from their paper showing some examples of species with conspicuous facial masks.

The paper suggests that mid-sized mustelids (rather than small or large) may be the most likely to benefit from an aposomatic face pattern because animals in this size range are both vulnerable to larger predators but big enough to put up a good fight. Weasels are smaller than the size where most species have conspicuous facial masks but they apparently have bigger anal scent glands that can produce a noxious odor. So perhaps they are like mini skunks and the conspicuous coloration warns of their stinky musk. Or, possibly, the face is a signal to other weasels to avoid two weasels mistakenly attacking each other if they happen to bump into each other while hunting. I could imagine mistakes could happen if weasels were to be similar in color to their prey—say a vole. Weasels are frenetic and therefore  likely to pounce quickly on suspected prey (a case of ‘shoot first and ask questions later’). This could be disastrous in a  weasel versus weasel encounter. Interestingly jumping spiders—also known for their fast pounce hunting style—seem to have such an intraspecific signaling system like this that reduces the risk of spider on spider predation.

Below. One other interesting feature of the coat color pattern of the long-tailed weasel is that northern populations have two coat colors each year, but southern ones do not. In northern populations, the animals molt into a white winter coat to match the snowy habitat in winter. Photo by Stuart McKay ‘borrowed’ from the web. This is a short-tailed weasel.

Below: The figure below shows the geographic distribution for two species with seasonal coat color changes in terms of the proportion of a local population that has a white winter coat (the rest remain in the brown pelage). In the weasel (shown on the right), in northern and montane populations everybody turns white in winter, which makes sense because of the presence of snow. In contrast, in southern and West Coast populations everybody remains brown year round, which also makes sense given the lack of snow. Interestingly, the areas in between these extremes have populations with mixtures of individuals: some individuals in the population turn white in winter, others do not. Various experimental studies have shown that these area with mixtures comprise genetic polymorphisms (i.e. winter coat color has a strong genetic basis). This figure is from a recent Science paper by Scott Mills and colleagues.

Other studies have why the natural selection drives some of these patterns—there is a higher risk of predation on animals that are mismatched in color from the habitat. In seasonal environments successful background matching involves two coat colors. Climate change has implications for how natural selection on coat color might change geographically due to changes in winter snow cover—some areas that used to have lots of snow in winter, and thus favoring the white coat type, are expected to lose that winter snow (or have fewer days with snow) as the climate warms, and a white coat type may no longer be favored. The paper by Mills et al. suggests that areas of genetic polymorphism may be particularly important as hot spots for dealing with this climate change induced natural selection.

Below: Another figure from the same paper showing the distribution of coat color types in relation to the number of days of snow at a location, for four species. Long-tailed weasel is the red curve.

Readers’ wildlife photos

October 22, 2021 • 8:00 am

We continue with the last of the Tree Swallow feeding photos from Emilio d’Alise. I reprise his introduction below (indented), and you can enlarge his photos by clicking on them.

Nest Competition,  Feeding, and Hovering

From 2007 to 2013, I lived in Colorado and worked in Woodland Park (8,100 ft. elevation). We had an empty lot next to the office, and we put up a Bluebird house. For the first three years, we had Bluebirds nesting in it, but in 2011, a pair of Tree Swallows (Tachycineta bicolor) moved in, and returned each year for the next three years. This post from 2011 documents the final weeks before that year’s brood fledged — they all fledged, but a hawk got one of them —and it includes photos and videos.

But, the year that I got serious about photographing them was 2012, and these are some of the photos from those sessions.

As I mentioned, the birdhouse is sized for Bluebirds, which are smaller birds, so the typical Tree Swallows brood of 5-7 makes for a pretty tight fit just before they fledge. Early on, the adults will enter the nest to feed the chicks.

On most feedings, a fair portion of the adult’s head goes inside the beak of the chick (both close their eyelids during contact) to ensure the meal is not lost. Still, occasionally, a few bugs fall out before the chick has a good grasp of it, probably because various parts of the bug may be stuck to the adult’s plumage.

On average, I would say at the peak (when I was shooting), the parents were coming by about every one to two minutes.

As far as I could tell, for a few weeks — from early morning to dusk — both adults did nothing but catch bugs and feed the chicks.


Readers’ wildlife photos

October 15, 2021 • 8:00 am

We continue with the series of Emilio d’Alise’s lovely pictures of swallows feeding their young (see first installment here).  Emilio’s captions are indented, and you can enlarge the photos by clicking on them.  I repeat some of the intro from the last series.

From 2007 to 2013, I lived in Colorado and worked in Woodland Park (8,100 ft. elevation). We had an empty lot next to the office, and we put up a Bluebird house. For the first three years, we had Bluebirds nesting in it, but in 2011, a pair of Tree Swallows (Tachycineta bicolor) moved in, and returned each year for the next three years. This post from 2011 documents the final weeks before that year’s brood fledged — they all fledged, but a hawk got one of them —and it includes photos and videos.

But, the year that I got serious about photographing them was 2012, and these are some of the photos from those sessions.

As I mentioned, the birdhouse is sized for Bluebirds which are smaller birds, so the typical Tree Swallows brood of 5-7 makes for a pretty tight fit just before they fledge. Early on, the adults will enter the nest to feed the chicks.

. . . On most feedings, a fair portion of the adult’s head goes inside the beak of the chick (both close their eyelids during contact) to ensure the meal is not lost. Still, occasionally, a few bugs fall out before the chick has a good grasp of it, probably because various parts of the bug may be stuck to the adult’s plumage.

On average, I would say at the peak (when I was shooting), the parents were coming by about every one to two minutes.

As far as I could tell, for a few weeks — from early morning to dusk — both adults did nothing but catch bugs and feed the chicks.

Here’s a swallow feeding its offspring a “pretty large bug”: a grasshopper:

Ducklings appear to swim behind mothers in a way that rides her wake and saves energy

October 10, 2021 • 9:30 am

Now my own personal observation of mallard ducklings following their mothers in Botany Pond shows that when she’s swimming slowly, a pack of them will clump behind her, as in the photo below (mine):

But when she’s booking it away from other ducks, the babies form a line behind her, like this (not mine):

Some other waterfowl show the same behavior when swimming in open water. Here are a pair of geese and their goslings (one adult brings up the rear as a guard):

Family of Canada geese swim across a pond- mother and father between 3 fluffy goslings

Have you ever asked yourself why? Wouldn’t a clump be better? Well, five researchers from China and Scotland asked themselves what advantage could possibly accrue to swimming in a line?

And they found one: it involves riding the waves of the duck ahead of you, and it benefits every duckling in the line. The phenomena involved are called “wave riding” and “wave passing,” and are explained briefly (and not very satisfactorily) in the short popular piece directly below at Phys.Org, which appears to be a press release from Glasgow’s University of Strathclyde.

Click on the screenshot if you want a quick explanation, but if you want to go into more depth, involving math and fluid mechanics, read the original paper two screenshots down. It’s from The Journal of Fluid Mechanics.

Here’s the original paper (click on screenshot); the entire reference is at the bottom and you can get a pdf from a link on the title page:

The explanation is simple but based on complicated modeling rather than observatin. And although at the end the authors claim that they now understand why ducklings swim in a line, they really don’t. They have proposed a model that, in my estimation, is a good explanation, but one that needs empirical testing. You have to look at the ducks!

Here’s how it works, in a model in which they’ve made some assumptions and used fluid-mechanic equations of drag in the water.

See the diagram below, with the arrows showing the hydrostatic force.

(b) When a duckling is swimming in calm water, its movement is impeded by the water drag alone, and there is “hydrostatic pressure force” that is exerted upward on the duckling’s belly.

(c) When a duckling is swimming on a wave with its breast on the wave’s crest and its belly in a trough, the hydrostatic force (arrows) works against the duckling’s movement, making it exert more energy than if it were swimming in calm water.

(d) However, when a duckling is swimming with its breast in the wave’s trough and belly on the crest, it is propelled forward by the wave, exerting less energy to swim than it would in calm water. It’s like surfing.

(From paper): (b), (c) and (d) shows a sketch of a two-dimensional duckling on a free water surface: (b) stationary in calm water; (c,d) swimming in waves with the same wavelength but different phase. Green curves denote the water surface. Blue curves denote the pressure on ducklings’ immersed body surfaces and the arrows denote the direction of the force.

And this is the explanation for why the first duckling “drafts” behind the mom, for mom’s swimming creates a series of waves behind her. You must assume that the duckling is the right distance behind her and riding the waves in position (d) above (assumptions not tested in the paper). As the authors note, it requires that the duckling’s forward speed must be equal to the mom’s (the velocity of the wave). This is called “wave riding”. But of course the duckling’s speed must equal Mom’s speed if it’s not to fall behind or go ahead.

The mother duck benefits too: she can get a reduction in wave drag of up to 35% by being pushed by the bow wave from the first duckling behind her. It’s a win-win situation.

What about the other ducklings in line?  Well, in the “wave passing” phenomenon, the other ducklings get a similar boost in movement so long as they’re the right distance behind the one ahead and so have their breast in the wave trough. All that’s required is that they keep the right distance from each other and move at the same speed as the mother. (They do of course move at that speed: that’s what keeps the line.) The first three ducklings get special benefits, but after that each succeeding duckling gets a smaller but still appreciable (and equal) boost, shown in the figure below (CDR represents the “reduction in drag” coefficient). Don’t ask me why it’s the first three who benefit most; it’s above my pay grade. ‘

Here’s a figure of a mom and six ducklings, showing the reduction in drag of each duckling on the y axis (height of blue dots). Duckling #1 gets the most benefits, then #2 and #3, and then the rest get equal benefits of wave-riding via wave-passing. The red lines show the wave profile.

(From the paper): (b) Wave drag reduction of each individual (blue dash line and columns). The red solid curve is the wave profile on the centre line behind the mother duck. Here 𝑑𝑛,𝑛+1 is the separation between two adjacent individuals, where the subscript 𝑛=0 represents the mother duck. The virtual ducklings are put in the positions of minimum wave drag. The error bar in panel (b) gives an indication of the errors induced by numerical discretization.

There would of course be an evolutionary advantage to babies swimming this way. And of course they don’t do the calculations, but those ducklings swimming the right distance behind the one before (a phenomenon that must itself evolve), have an energy advantage compared to off-wave ducklings, and that means better survival and reproduction. The authors add that “These principles could be potentially applied to design modern freight carrying vessels, e.g. a water-train to transport more cargoes without extra fuel cost.”

So that’s the story. And yes, it is a story, but a good one.  How do we test it? It’s not that difficult: you simply measure where the ducks are swimming behind the mother, seeing if they are indeed riding her wave. It’s harder than it looks, but surely not beyond doing! (I should add that a single duckling swimming in front of the mother gets a bow-wave push, but that doesn’t work for multiple ducklings, and there’s a protection and navigation advantage of swimming behind and not in front of Mom.)

It should be tested, for it’s a simply explanation for an observation that many have made, but none have queried.

Here’s one caveat I thought of. We know that ducklings sometimes follow in a line behind Mom when they’re walking on land. Here’s a photo:

There are two questions: does this reflect an advantage different from that of wave-riding and wave-passing? Why aren’t they walking in a clump? And if there’s an advantage of terrestrial locomotion in this way, perhaps the explanation above is wrong or insufficient. On the other hand, my own guess would be that mallards are only infrequently on land with their babies compared to being in the water with them. I suggest, then, that single-file following evolved for water locomotion and is automatically followed as a instinctive byproduct when they’re moving on land. Who knows?

This is exemplified in the famous “Make Way for Ducklings” statue on the Boston Common, honoring the famous children’s book:

My own photo from 2016:

h/t: Steve


Yuan, Z., Chen, M., Jia, L., Ji, C., & Incecik, A. (2021). Wave-riding and wave-passing by ducklings in formation swimmingJournal of Fluid Mechanics, 928, R2. doi:10.1017/jfm.2021.820