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Fast-Swimming Swordfish Automatically Lubricate Themselves

Broadbill Swordfish in the Mediterranean Sea off Italy.
Broadbill Swordfish in the Mediterranean Sea off Italy.

Swordfish steaks frequently appear on menus and dinner plates around the world. But even though many people have hooked, hacked apart, and devoured these majestic fish, few truly understand their bodies. Indeed, until John Videler from Leiden & Groningen University started studying swordfish, no one knew that they had a fist-sized gland in their heads, which slathers lubricating oil over their famous pointed snouts.

Videler has been studying the physics of swimming fish for most of his career, and swordfish were particularly intriguing to him because they’re such superlative swimmers. It’s commonly said that they can reach speeds of 100 kilometres per hour (62 miles per hour), and although the provenance of that estimate is dubious, there’s little doubt that they are really, really fast. So in 1994, while teaching a diving course in Corsica, he bought a swordfish bill from a local fisherman and started studying it.

When a swordfish swims, layers of water flow along the surface of its bill. As it picks up speed, these currents threaten to break away, creating swirling areas of turbulence that increase the drag upon the animal.

But Videler found that the bill is rough, like sandpaper. This limits any turbulence to a thin layer close to the bill, and prevents the larger, destabilising eddies from forming. The bill is also pitted with small, interconnected holes near its tip, which stop water pressure from building up at the fish’s front end—again, this reduces drag by preventing turbulence.

By then, Videler was hooked. He got two more swordfish from the same fisherman, and persuaded Ben Szabo—the head of radiology at Groningen University—to put them in a medical MRI scanner. The team scanned the fish heads between 2 a.m. and 5 a.m., when the machine was available.

At first, the images were confusing and hard to interpret. But when Videler dissected the heads themselves, he noticed a large oily gland above the base of the bill and between the animal’s eyes. And sure enough, there it was on the scans.

He thought nothing of it until 2005, when a student named Roelant Snoek came to him with an interest in swordfish. Videler told him about the gland, and suggested that it might connect to the fish’s olfactory system, influencing its sense of smell. But Snoek couldn’t find any such connections.

After much frustration, he finally worked out the gland’s true purpose by accident. While taking photographs of a swordfish head, he accidentally dropped a lightbulb onto it. The bulb illuminated a web of tiny blood vessels inside its skin, and Snoek showed that these were connected to the gland. The vessels then open out into the fish’s skin via tiny pores, each just a fraction of a millimetre wide. Snoek proved this by heating the gland with a hair-dryer; once hot, the congealed oil became liquid and oozed out the fish’s pores.

So Videler thinks that the gland is yet another drag-reducing adaptation. Its oil repels water and allows incoming currents to flow smoothly over the surface of the bill. That depends on the oil staying warm, but swordfish have a solution for that, too. They have modified some of their eye muscles into heat-producing organs that warm their blood and sharpen their vision as they hunt. This same heating effect could liquefy the drag-reducing oil, allowing it to ooze out of the glands just as the fish have the greatest need for speed.

The oil might explain another weird feature of swordfish anatomy. They are among the only fish with a concave hollow at the front of their heads—an slight inward-curving bowl that, counter-intuitively, ought to increase drag. “I’ve been puzzling about that for years,” says Videler. He now thinks that the hollow is shaped so that water flowing past it creates an area of low pressure, which sucks the oil out of the fish’s gland.

If he’s right, it means that a fast-swimming swordfish automatically lubricates itself.

This makes a lot of sense, but it’s still a hypothesis. “We still have to find some way of doing experiments to visualise the flow of water [over the bill],” Videler admits. “We can’t do that on live swordfish,” since these animals are impossible to keep in captivity. But he hopes that other scientists could run fake swordfish—sandpaper skin, pores, oil, and all—in water tunnels to see how they perform.

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Seagulls Are Carrying a Dangerous Superbug Through the Skies

A European Herring Gull (Larus argentatus) takes off.
A European Herring Gull (Larus argentatus) takes off.
Photograph by Ben Cranke

A superbug that’s resistant to the absolutely last-ditch antibiotic colistin has been reported in seagulls on two continents—pinpointing one way, though almost certainly not the only way, that this dangerous drug resistance is moving around the world.

Since last November, when researchers in England and China announced the discovery of bacteria able to survive colistin, there has been an explosion of people looking for that resistance, and finding it. Scientists have published almost 100 reports of colistin resistance—known as MCR and conferred by a gene that’s been dubbed mcr-1—in almost two dozen countries.

It has been found in human patients, including a woman in the United States in May; in livestock, which get the drug on intensive farms, and are probably the original source of the problem; and even in pets.

Now, in letters to the Journal of Antimicrobial Chemotherapy, two research teams in Lithuania and Argentina report that they trapped birds and swabbed their butts, or scooped up seagull droppings, and found the resistance-conferring gene in E. coli being carried by two species: herring gulls in Lithuania (Larus argentatus) and kelp gulls in Argentina (Larus dominicanus). 

Both teams think the birds probably picked up the resistant E. coli by eating garbage, which may have contained sewage or medical waste. (The organisms in the South American gulls also contained another important type of antibiotic resistance, known for short as ESBL.)

This isn’t the first time that gulls have been identified as possible carriers of antibiotic-resistant bacteria. In 2011, French researchers found multi-drug resistant E. coli in seagull droppings in Miami Beach, and those researchers and others earlier found resistant bacteria in gulls in Portugal, France, Russia, and Greenland.

The point in all those stories, as well as in the new reports, is that gulls migrate, from hundreds to thousands of miles depending on the species—so they could serve as a vehicle for carrying resistant bacteria somewhere new.

Gulls migrate, from hundreds to thousands of miles, so they could serve as a vehicle for carrying resistant bacteria somewhere new.

“The lifestyle of gulls allows them to carry and disseminate pathogenic and resistant microorganisms despite country borders,” the Lithuanian researchers say in their report. “Water contaminated by feces of birds should be foreseen as an important risk factor for transmission of resistant bacteria.”

The undetected movement of bacteria is especially important in the case of MCR, because the discovery of colistin resistance is truly alarming. Colistin is an old drug that medicine consigned to the back of the shelf in the 1950s because it is toxic, and only recently started using again because so many other antibiotics have been undermined by overuse in medicine and agriculture.

The gene that creates colistin resistance is on what is called a plasmid, a loop of DNA that isn’t bound up in chromosomes but can move easily between bacteria. That has scientists worried that the gene could move into disease organisms that already possess resistance to other antibiotics, creating a superbug that would be completely untreatable.

Kelp gull (Larus domicanus) perched on rock, Caldera, Chile.
Kelp gull (Larus domicanus) perched on rock, Caldera, Chile.
Photograph by Chris Mattison

So far, mcr-1 has been found in the United States three times: in two stored samples from slaughtered pigs that were stashed in a U.S. Department of Agriculture database, and in a 49-year-old woman in Pennsylvania, not identified by name, who went to a clinic for help with a urinary tract infection.

At a meeting Tuesday afternoon in Washington, D.C., of the Presidential Advisory Council on Combating Antibiotic-Resistant Bacteria, federal officials relayed that the woman has recovered from her infection, but still continues to carry the highly resistant bacterium in her system. Dr. Beth Bell, director of the National Center for Emerging and Zoonotic Diseases at the Centers for Disease Control and Prevention, also said that 99 of the woman’s family members and close contacts have been checked, and none of them are carrying bacteria containing mcr-1, reinforcing the mystery of how the resistant bacteria reached her.

Bell and representatives of the U.S. Department of Agriculture said the gene remains rare in the U.S.: The CDC has checked more than 55,000 stored samples collected from patients, animals, and food, and the USDA is checking 2,000 additional samples that it has stored. So far, that search has revealed only the two samples from pigs that were slaughtered in Illinois and South Carolina.

The officials commenting Tuesday agreed that there may be no way of tracing the path that MCR took to reach the U.S.—the bacteria may have spread from another person, or on food—and that the key thing now is to build surveillance systems that alert health planners as it moves.

“The good news is we found it,” observed Dr. Martin Blaser, a professor of medicine and microbiology at NYU Medical Center and chair of the Presidential council. “The bad news is, it’s here.”

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Birds on Islands Are Losing the Ability to Fly

Before the arrival of humans—and the rats, cats, and other predators that we brought—New Zealand was an idyllic haven for birds. Without ground-dwelling mammalian hunters to bother them, many of the local species lost the ability to fly. There’s the kakapo, a giant, booming parrot with an owl-like countenance; the takahe, weka, and other flightless relatives of coots and moorhens; a couple of flightless ducks; and, of course, the iconic kiwi.

Kakapo (Strigops habroptilus) at night, Codfish Island, New Zealand. Photograph by Stephen Belcher, Minden Pictures, Corbis
Kakapo (Strigops habroptilus) at night, Codfish Island, New Zealand. Photograph by Stephen Belcher, Minden Pictures, Corbis

These birds are part of a pattern that plays out across the world’s islands. Wherever predators are kept away by expanses of water, birds become flightless—quickly and repeatedly. This process has happened on more than a thousand independent occasions, producing the awkward dodo of Mauritius, the club-winged ibis of Jamaica, and the tatty-winged flightless cormorant of the Galapagos.

The call of the ground is a strong one, and it exists even when the skies are still an option. Natalie Wright from the University of Montana demonstrated this by collecting data on 868 species. She showed that even when island birds can still fly, they’re edging towards flightlessness. Compared to mainland relatives, their flight muscles (the ones we eat when we tuck into chicken breasts) are smaller and their legs are longer.

“Pretty much all island birds are experiencing these pressures to reduce flight, even if some can’t go to the extreme,” Wright says.

Her results show that flying isn’t a binary thing, with a clear boundary between taking to the air and staying on the ground. Instead, there’s a full spectrum of abilities between aeronautical swifts and shuffling kiwis, and island birds exist on all parts of that continuum. “None of the species I looked at were flightless or close to being truly flightless,” says Wright. “There’s no point where, all of a sudden, they have much smaller flight muscles.”

Her study began about 20 years ago, when her undergraduate advisor David Steadman started weighing the flight muscles of birds at the Florida Museum of Natural History. When Wright got her hands on the data set, she noticed that fruit doves had smaller flight muscles on islands that were further from the mainland. She then travelled to five natural history museums herself to examine more skeletons. For each one, she measured the long bones in the lower legs and the size of the breastbone—the latter revealed how heavy the bird’s flight muscles would have been in life.

Across nine major groups of birds, with a wide range of lifestyles, body shapes, and diets, Wright found the same trend. On smaller islands with fewer species, no mammalian predators, and fewer birds of prey, birds have repeatedly reallocated energy from forelimbs to hindlimbs, away from big flight muscles and towards longer legs.

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To her surprise, the trend even applied to hummingbirds, for whom flying is an inextricable part of life. Hummingbirds hover in front of flowers to drink nectar. A flightless hummingbird is a dead hummingbird. And yet, even though “islands hummingbirds look like hummingbirds when they fly, they were still reducing their flight muscles and evolving longer legs on islands without predators,” says Wright.

The same was true for kingfishers, flycatchers, tanagers, honeyeaters, and other groups that are extremely dependent on flight. Wright studied the Todiramphus kingfishers across 27 Pacific islands. “Members on islands with fewer than 20 species of birds, which don’t have any predators that can kill an adult kingfisher, have much smaller flight muscles and much longer legs than any members on larger and more populated islands,” she says. “They sit on perches and fly out to grab prey. Their foraging style requires flight, but they’re edging towards flightlessness.”

Why? It’s easy to see why a diving bird like a cormorant or a ground-dwelling one like a kakapo might lose its ability to fly when predators are absent. But why should a hummingbird or kingfisher, which flies all the time, sacrifice some of its aerial prowess?

Because flight muscles come with a cost. Even at rest, larger ones require more energy to maintain. So if birds can get away with smaller ones, evolution pushes them in that direction. Large flight muscles are especially useful when birds take off. That’s the most energetically demanding part of flying, and the bit that’s most important for escaping from ground predators. If such predators are absent, birds can take off at a more leisurely pace, and they can afford to have smaller (and cheaper) flight muscles. (This might also explain why they developed longer legs: they take off more by jumping than by flapping.)

Wright’s results suggest that island birds might be more vulnerable to introduced predators than anyone appreciated. Even those that can fly aren’t as good at it as their mainland counterparts. They may also help to explain why island birds diversify into such wondrous forms. When they settle in a remote landmass, even the flying ones might quickly lose the power they need to cross oceans and find new homes.

Islands, it seems, create birds that stay on islands.

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Weird Worms Swim in Huge Green Circles

FLPA, Alamy
FLPA, Alamy

If you find yourself walking along the beaches of the English Channel, you might come across a mat of green goo, as if someone had tipped a jar of mint sauce onto the beach. But if you get down on your hands and knees, and stare at the goo with a magnifying glass, you’ll see its true nature.


Little green worms, each just a few millimetres long, writhing together in their millions.

Their formal name is Symsagittifera roscoffensis, but Channel Islanders call them mint sauce worms for obvious reasons. Their green colour comes from the algae in their bodies, which provide them with nutrients by harnessing the sun’s energy. The algae also gave the creatures their other name, favoured by early 20th century biologists: “plant-animals.”

One of those biologists, Frederick Keeble, wrote a whole book about these creatures in 1901. Eight decades later, Nigel Franks from the University of Bristol picked up a copy at a second-hand bookstore for the princely sum of 50 pence. Intrigued, he set out to find them, and it took him several trips to the island of Guernsey to do so. “It’s hard to find a patch of them but once you find them, they’re there in huge numbers,” he says. “They’re hugely impressive. When you see them, you’ll think they’re algae.”

Franks scooped up a group of them and started studying their behaviour. He quickly realised that if he added enough of them to the same pool of shallow water, they’d start swimming in mesmerising circular mills, with hundreds of individuals in rotating green rings. “They did them at the drop of a hat,” says Franks. “It was such a telltale symptom of really strong social interactions.”

Having spent most of his career studying the collective behaviour of ants, Franks was the perfect audience for the worms’ display. He knew that many other social animals will produce circular mills, for varying reasons. Army ants do it if you isolate a group of them, slavishly following each other’s chemical trails until they die from exhaustion. Fish do it when confronted by predators. Even virtual animals will form mills if you program them with simple rules. So what about the worms?

By studying videos of the animals, Franks and his colleagues showed that they interact strongly with one another, often swimming in parallel with just a millimetre between them. As their densities increase, they grew disproportionately closer. The mills, it seems, arise from these close-quarter interactions, and from the worms’ tendency to curve in a particular direction. (It’s notable that almost all the mills spin clockwise.)

Using this information, Franks’ colleague Alan Worley built a computer simulation in which virtual worms behaved according to simple rules, and yet spontaneously produced circular mills just like their real counterparts.

Green mint sauce worms.
Green mint sauce worms.
Photograph by Stevie Smith

“But many different models of individual interactions can reproduce the same kind of collective patterns,” says Guy Therauluz, another collective motion researcher at Paul Sabatier University. “Deciphering the real social interactions at work between worms is a task that remains to be done.”

Franks plans to do that. It’s possible, he says, that the worms are dribbling some kind of chemical behind themselves, which the others follow. Or perhaps they are reacting to turbulence in the water. “The rules have yet to be worked out,” he says.

He also wants to know why the worms behave in this way and he has a fascinating suggestion. Perhaps the worms are social sunbathers. By gathering in large mats of biofilms, bound together by mucus that they themselves secrete, they can stabilise their position on sandy beaches or tidepools. In Franks’ words, they “behave collectively as a social seaweed”.

Individual worms are also known to head towards light sources that are almost too bright for them, and would max out the abilities of their algal partners. They could deal with that problem in a mat by ducking down into the darker centre once they’ve had their fill of light. Franks compares them to emperor penguins huddling against bitter Antarctic winds: these flocks continuously rotate as individuals at the edge wheedle their way into the centre.

Dora Biro from the University of Oxford praises Franks’ attempt to explain not just the how of the collective motion, but also the why—something that has been overlooked by scientists in this field.  “The hypothesis is very interesting,” she says. “It would be great to find support for it through future work, including observations in the wild on the formation of the biofilm, and the role of milling in the process.”

Franks is just getting started with the mint sauce worms, but he sees them as great subjects for understanding collective behaviour in animals. Other scientists have analysed their bodies, the way they grow, and their powers of regeneration—but only ever one at a time. “I suspect that if people looked at populations more, as we have been fortunate enough to do with these things, they’d see more and more examples of strange microscopic organisms showing social behaviour like this,” Franks says.

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Flies Could Falsely Place Someone at a Crime Scene

The Australian sheep blowfly doesn't just eat nectar. It has a taste for a particular human body fluid—and it’s not blood.
The Australian sheep blowfly doesn’t just eat nectar. It has a taste for a particular human body fluid—and it’s not blood.

This might be the grossest science experiment I’ve ever written about—which is really saying something on a blog called Gory Details—but it’s also one of the most fascinating. It has to do with the taste a certain type of fly has for human bodily fluids.

Blowflies, in case you’re not familiar with them, are the flies of death. As I learned when rats died in my ceiling, these big shiny flies have an amazing ability to appear seemingly out of nowhere within moments of blood being spilled or at the slightest whiff of decay.

So, a lot of blowflies are sometimes found buzzing around a gory crime scene. That got forensic expert Annalisa Durdle wondering: With all those flies doing what flies do—flying around and pooping on stuff—could they be contaminating crime scenes?

“Interestingly, fly poo can also look very similar to blood spatter,” says Durdle, who studied forensic science at La Trobe University in Melbourne, Australia.

“Anyhow,” she e-mailed in response to my indelicate questions about her research, “it turns out that you can get full human DNA profiles from a single piece of fly poo. (I tend to refer to poo rather than vomit because in my experience flies tend to eat their vomit and most of what you have left is poo—although they do eat that too!)”

Clearly, blowflies are gross.

But could they falsely incriminate someone? To find out, Durdle needed to know what blowflies would really eat at a crime scene.  

So she did the experiment. Her team offered Australian sheep blowflies a crime scene buffet, with body fluids collected from volunteers—blood, saliva, and semen—plus other snacks that flies might find in a victim’s home: pet food, canned tuna, and even honey.

“You draw more flies with honey,” my mother always told me. But in this case, she was wrong.

What you draw more flies with, it turns out, is semen.

“It’s the crack cocaine of the fly world,” Durdle says. “They gorge on it; it makes them drunk (they stumble around, partly paralyzed—I’ve even seen one fly give up hope of cleaning itself properly and sit down on its bum!). Then they gorge some more and then it kills them. But they die happy!”

Video: Meet Annalisa Durdle, the coolest fly-poop scientist ever.

The flies liked pet food too, but weren’t much into blood, and they were really uninterested in saliva. Maybe they go for semen’s higher protein content—it contains more than 200 different proteins, at much higher levels than in blood. (Update: or maybe not. Protein levels vary, and Annalisa Durdle notes that “flies are like people—they don’t necessarily eat what is good for them!” Flies are attracted to various aromas, including sulphur-based ones, so it may be that semen is simply more alluring than other food sources.)

Another thing semen has plenty of: DNA.

Durdle tested flies’ poop after various meals. “If the flies had fed on semen or a combination with semen in it, then you got a full human DNA profile almost every time. With blood, it was maybe a third of the time and with saliva, never.”

“It was also interesting to find the flies generally preferred dry blood or semen to wet blood or semen,” Durdle says. “This could be important, because it means flies could continue to cause problems at a scene long after the biological material had dried.”

How big a deal is this? Durdle says, “You really need to look at the probabilities… the chances that a fly might feed on some poor guy’s semen (after he’s had some innocent quiet time to himself), and then fly into a crime scene and poo, potentially incriminating him.”

There’s also the chance that a forensic investigator could sample fly poop thinking it’s blood spatter, she says, and find DNA that’s not from the victim.

A fly might occasionally be helpful to the cause of criminal justice. If a fly eats bodily fluids from a crime scene and then flies away into another room and poops there, it might save a sample of DNA from the perpetrator’s attempts to clean up.

Flies aren’t the only potential problem for interpreting DNA. As the technology used in forensic labs has become more sensitive, there’s greater risk of picking up tiny bits of DNA transferred to a crime scene, forensic scientist Cynthia Cale argued last year in Nature.

In fact, Cale showed that one person can transfer another person’s DNA to a knife handle after two minutes of holding hands. (Next she says she’ll try shorter times, to see if even a brief encounter could transfer DNA.)  

The fly-poop research is interesting, Cale says. Blowflies would probably be more likely to transfer DNA within a crime scene rather than bringing it in from outside, but even that could confuse the reconstruction of a crime.

“I think the biggest impact might be when a defense lawyer uses it to raise doubt in the mind of a jury,” Durdle says.  


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Amazing Video Reveals Why Roaches Are So Hard to Squish

No door will stop them: American cockroaches can squeeze through a space just three millimeters high.
No door will stop them: American cockroaches can squeeze through a space just three millimeters high.
Photo Credit Tom Libby, Kaushik Jayaram and Pauline Jennings. Courtesy of PolyPEDAL Lab UC Berkeley


Have you ever stomped a roach, just to have it skitter away unscathed?* Or seen one disappear into an impossibly small crack?

Now scientists have figured out how they do that, and the results are terrifying.

The American cockroach (Periplaneta americana, aka “the big ones”) can squeeze through a crack the height of two stacked pennies in about a second—a fact newly discovered by two brave scientists who are probably still seeing roaches squeezing under the doors of their nightmares.

See for yourself:

Not only can roaches fit through tight spaces by flattening their flexible exoskeleton and splaying their legs to the side, the researchers found, they can keep running nearly as fast while squished, the team reports Monday in the Proceedings of the National Academy of Sciences. (In roach terms, top speed is 1.5 meters, or 50 body lengths, per second. Scaled up, that’s equivalent to a human running 200 miles per hour.)

Robert Full and Kaushik Jayaram at Berkeley built tiny tunnels and used a roach-squishing machine to test the animals’ limits. (No roaches were harmed—Full says “we only pushed them to 900 times their body weight, and they could still do that without being hurt.” In fact, they ran just as fast afterward.)

“We find them just as disgusting and revolting as everybody else,” Full says. But he also thinks they’re amazing, and is designing roachy robots that can squeeze and scuttle just like the real thing. The robots take inspiration from roaches’ jointed exoskeletons, with a design similar to folded origami.

A new compressible robot, nicknamed CRAM, is inspired by the flexible yet tough cockroach.
A new compressible robot, nicknamed CRAM, is inspired by the flexible yet tough cockroach.
Photograph by Tom Libby, Kaushik Jayaram and Pauline Jennings. Courtesy of PolyPEDAL Lab UC Berkeley

Full sees roaches and other arthropods—insects, spiders, and the like—as the next big thing in robots inspired by nature. Unlike other soft robots inspired by worms or octopuses, insect-bots with hard exoskeletons and muscles could run fast, jump, climb, and fly, while still remaining flexible.

“We know that cockroaches can go everywhere. They’re virtually indestructible,” Full says. For roaches, being able to scuttle quickly through small spaces has allowed them to spread into virtually every habitat imaginable and outrun their competition. Other insects probably have their own versions of these super-squishing superpowers, too, he says.

(For more on the positive side of roaches, learn why cockroaches made it onto our list of “All-Star Animal Dads.”)

The new roach study “transformed how I view a seemingly ‘hard’ animal,” says Daniel Goldman of Georgia Tech, who studies the physics of animal movement.  

“Their idea to create a “soft” robot out of deformable “hard” parts is great, and should transform how we think of creating all-terrain robots,” Goldman says.

*If you would never, ever, stomp on a roach, and are horrified at the suggestion, you’re a kind person and a sensitive soul. Keep watching the video though—it may surprise you.

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You’ll Find the Biggest Male Appendage in the World—at the Beach

So tell me: Of all the males on our planet—and I’m talking all, scale be damned, from the littlest insects to the biggest of whales—who’s got the most impressive appendage? Who (you should pardon the expression) is our Biggest Daddy?

And I don’t mean just sex organs, impressive as they sometimes are. I’m talking about any outstanding male appendage—whatever guys have that thrills the ladies, the obvious non-penile example being the peacock tail, which as we all know when fully displayed makes peahens dream of George Clooney.

Picture of a peacock with its feathers fanned out
Photograph by Richard I’Anson, Getty
Indian Peafowl, or Peacock, displaying tail feathers.. Photograph by Richard I'Anson

Impressive? Yes. The problem being that between trysts, a superheavy tail must be a drag to lug around. It costs energy to maintain and more energy to get up and unfurled. But the drive to reproduce is a powerful thing, and sexual selection, as Darwin taught us, just keeps pushing the limits of bigness.

Obviously, there is such a thing as too big. I imagine it gets awkward to be a walrus with tusks curling dangerously close to your chest.

Picture of a pacitic walrus with very long tusks lying on rocks
Photograph by Yva Momatiuk & John Eastcott, Minden Pictures / National Geographic
Pacific Walrus (Odobenus rosmarus) bull portrait on coastal rocks in haul-out cove, summer, Round Island, Bering Sea, Bristol Bay, Alaska. Photograph by Yva Momatiuk & John Eastcott / Minden Pictures / National Geographic

And the weight of these things? Not the absolute weight, but the proportional weight—that’s another limitation. How much can a guy carry? According to Douglas Emlen in his wonderful book Animal Weapons: The Evolution of Battle, while the rack of bone that sits atop a male caribou is hugely impressive (those antlers can weigh 20 pounds and stretch five feet across) …

Picture of a caribou with large antlers amid a lush green landscape on a misty day next to an equal sign that says ''8%''
Photograph by Bob Smith, National Geographic Creative
Close up portrait of a male caribou, Rangifer tarandus. Photograph by Bob Smith, National Geographic Creative

… as big as they are, they account for only 8 percent of the male’s total body weight. Moose and elk have even larger antlers, but even the biggest elk antlers equal only 12 percent of its body weight. So that’s doable. Once upon a time, 11,000 years ago, there was a deer (called Megaloceros giganteus, or the Irish elk) that wandered Europe and Asia, and those guys had boney tops so insanely branched, so crazily big, that our prehistoric humans painted them worshipfully onto the cave walls at Lascaux.

Picture of an Irish elk painted onto the wall at Lascaux cave next to a ''less than'' sign that says 20% next to it
Photograph by Sisse Brimberg, National Geographic Creative
Prehistoric artists painted a red deer on a cave wall. Photograph by Sisse Brimberg, National Geographic Creative

But even these antlers, 12 feet across and wildly branched, weighed less than 20 percent of the total animal.

Go Small to Get Big

You have to drop down to the insect family, to a group of horned beetles, to find a big appendage that approaches a third of the animal’s body weight. There are several beetles that have fighting, clamping horns almost the size of their bodies, and a thing like that growing out of your skull, writes Emlen, “is a little like having your leg sticking up out of your forehead.” You feel it.

Picture of a rhinocerous beetle on wood
Photograph by altrendo nature, Getty
Rhinoceros Beetle, male, Columbia, South America, Photograph by altrendo nature

But if you’re looking for the male who wears the crown, whose appendage is so big, so startling, so colorful, so attractive, so monstrous, and therefore unequaled in the animal kingdom—if you’re looking for the champ? Well …

He’s not in the African savannah. He doesn’t have a tusk. He’s not especially large. You have to look down to see him, down near your feet when you’re at the beach. This is him:

Picture of a fiddler-type crab standing on sand and waving a claw in the air
Photograph by Michael Nichols, National Geographic Creative
Loango National Park, Gabon. A fiddler-type crab with claw raised standing outside its burrow, Photograph by Michael Nichols, Getty

He’s a fiddler crab. And that appendage is his claw. And while sizes vary from crab to crab, the biggest fiddler crab claws weigh roughly half the body weight of the animal. Half! That’s nature’s biggest appendage, says Emlen. And what is it for? Not for feeding. The claw is useless at mealtime. Males eat with their other, smaller claw only. But, says Cornell biologist John Christy, the claw’s bright colors definitely attract female attention. It can also snap down and inflict real harm, so they’re potential weapons. But mostly, he discovered, males use them—I kid you not—to wave.

“Up and down, up and down, again and again,” writes Emlen, “they raise their claws high and drop them. Dozens of times each minute, thousands of times per hour, hour after hour … ” They look a little silly doing this, like a lonely fan trying to start a stadium wave. Check out this fellow:

Why are they waving? It’s a warning. “Look what I’ve got!” the male is saying to any male who would trespass into his burrow. “This thing is going to pound you if you come near, so stay away!” In effect, Emlen writes, “fiddlers are employing their claws as warnings rather than instruments of battle.” And it works. “An overwhelming majority of contests end before they ever begin, without anything even resembling a fight. A mere glance at a big claw is sufficient to deter smaller males.”

The male has built a tunnel, which leads to a nesting burrow. His claw has attracted a lady, and she’s down below raising his family. His job is to stay on top, waving till she’s done or he drops. It’s a tough life, lifting that gigantic appendage over and over, using up energy, constantly getting bothered by would-be challengers. The male can’t eat. Not while he’s guarding. His food is at the water’s edge, which is down lower on the beach. So he stands there, day after day, getting hungrier, until eventually, Emlen says, “Even the best males run out of steam and are forced to abandon their burrows to go feed and refuel. The instant they leave, others will claim their burrows.” And then they become challengers and have to start all over again.

So while it may be glamorous to top the list of Biggest Appendage Ever, what with the lifting, the waving, the straining, the not eating, the worrying about how long you’ll last, it might be better to have a medium-size claw and not have to be always worrying about the biggest bullies at the beach. Yes, the big claw does dramatically increase your chances of producing babies, which, as Darwin will tell you, is the whole point. But if I were a fiddler crab lucky enough to have the biggest appendage in the world, I think I’d get myself a nail file (claw file?), erase my genetic advantage, and spend lazy afternoons sipping pond scum by the ocean’s edge. I like a gentler life.

Douglas J. Emlen’s book, Animal Weapons: The Evolution of Battle, is a fascinating account of how animal weaponry, both offensive (claws, horns, teeth) and defensive (armor, shelter, thorns, claws again) parallel human weaponry, both offensive (arrows, lances, swords, missiles, A-bombs) and defensive (armor, castles, spying). It’s a compelling, fun, often scary analysis. And David Tuss’ drawings, especially his animals, made me jealous.

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Baboon-Trackers Herald New Age of Animal Behaviour Research

Picture a troop of olive baboons, moving over the savannah. There’s around fifty of them, and they cover a lot of ground as they search for grass, seeds, insects, and other bits of food. They need to stick together so they don’t get eaten, but different animals might want to head in different directions at any one time. How do they coordinate their choices to preserve the sanctity of their group? As primate researcher Joan Silk says, “It’s hard enough to get two adults and two kids into the car at the same time let alone 50 baboons who can’t talk.”

It’s a fairly simple question—how do animals make decisions as a group?—but it’s also incredibly hard to answer, even for animals like baboons that have been actively studied since the 1950s. A field-worker can easily track a single baboon, or even a few. But she can’t track all 50 at once, let alone note down who’s getting up, who’s leading, and who’s following, over long periods of time.

She can, however, turn to technology. By fitting wild olive baboons with sophisticated GPS collars, which automatically record their movements, Margaret Crofoot from University of California, Davis had learned exactly how they make decisions about where to go and whom to follow. Some of her results are surprising, others are more intuitive; regardless, her study heralds a new age of zoology, in which scientists can analyse animal behaviours on a scale that was previously impossible.

For several years, Crofoot had been using radio-trackers on wild capuchin monkeys, to study how they fend off predators and fight other monkeys as a group. “I was getting increasingly interested in how individual decisions scale up to group behaviours,” she says, “but you can’t watch everyone at once.” Then, she heard about the collars.

GPS collars aren’t new but they often have poor temporal resolution. They might take a reading once every few hours, for example—good enough to track a migrating bird. Newer models are much more sensitive and can take readings once a second—good enough to track a running cheetah. “I thought, wow, if you could put these collars on primates, you could do all these studies on an intact social group, living in its natural habitat,” says Crofoot.

Olive baboons were an obvious choice. They’re well-studied, so their behaviours can be interpreted in the light of decades of knowledge. They live in open habitats, where GPS signals are strong and good. And unlike many other monkeys which scamper through trees, baboons live on the ground, making them easier to follow, trap, and collar.

A troop of olive baboons. Credit: Stig Nygaard
A troop of olive baboons. Credit: Stig Nygaard CC-BY-2.0

The hardest bit was actually finding the right troop. Many researchers have spent a lot of time in habituating baboons to their presence, and they were concerned that trapping the individuals would wreck that hard-earned tolerance. So Crofoot worked with a troop in Kenya’s Mpala Research Centre, which weren’t part in any other studies. Over a week, her team caught and collared 25 of the individuals.

Once the data were in, team members Ariana Strandburg-Peshkin and Damien Farine worked together to interpret it. They wrote a programme that would automatically identify events where, say, one baboon walked off and others followed, or when one walked off and then returned to the same spot. The video below shows 25 minutes of movements, sped up 25 times.

Surprisingly, they found that a baboon’s rank in the pecking order didn’t affect its odds of being followed. Rank matters a lot in baboon society, and affects how much sex, food, and support each individual gets. When making foraging decisions, the dominant males wield a despotic hold over the rest of the group, enforcing choices even when they’re the wrong ones.

But when it comes to more mundane decisions like “Where should we go?”, their tyrannical sway isn’t evident. The data revealed that the troop members didn’t weigh the movements of dominants any more heavily than those of subordinates. Age and sex didn’t matter either. “It’s a little surprising that dominants aren’t using their social power to drive group decision in ways that are beneficial to them,” says Crofoot. “It seems that on a day-to-day level, most decisions are made more democratically.”

The team also showed that what happens if baboons have differences of opinion. If two baboons move off in different directions, but at the same time, the angle between their paths determines what the others do. If that angle is small—say, less than 90 degrees—other baboons will split the difference and head off in the average direction. If the angle is big, the followers make a choice, and trail one initiator or the other.

That’s rather astonishing—not because of the rule, but because it exactly follows what Iain Couzin from Princeton University predicted a decade earlier, using just mathematical theory and computer simulations. Couzin, a leader in the field of collective behaviour and a collaborator in Crofoot’s study, modelled the movements of animal groups, creating digital swarms in which individuals were all the same and had no special relationships. By contrast, identities and relationships are paramount in baboon society. And still, “the simple model predicted the behaviour of the very complex social group,” says Crofoot. “We were really struck by just how closely the patterns matched.”

“It’s a great study, and really innovative,” says Joan Silk from the University of California, Los Angeles. “We’ve been perplexed for many, many years about how animals in groups figure out where to go next, and how the process of group movement is coordinated and negotiated. It’s been impossible to quantify the movement patterns of multiple individuals at the same time. But now, we can do this.”

This is just the beginning. The team have uploaded their gargantuan pile of data to Movebank—a free, online database of animal tracking data—so that others can have a play. They also have plans for more analyses of their own.

For example, Strandburg-Peshkin says that individuals baboons do vary in their odds of being followed—it’s just that this variation doesn’t correlate with anything obvious like sex, age, or dominance. What then? What makes one animal a likelier leader and another not? Is it something about where they sit in the group, in physical space rather than social hierarchy? For that matter, what determines where individuals sit, and how do their positions change as the group shifts and moves? And what happens when a stationary group decides to travel? “How do you overcome the inertia of whole bunch of baboons sitting around?” asks Crofoot.

Strandburg-Peshkin also notes that they only looked at data from one baboon troop, and she’d like to know if other groups—or other animals—show the same patterns. A decade ago, that would have been wishful thinking. Now, with improvements in GPS collars, flight trackers, and related tech, it’s a plausible expectation. We’re entering a new age in the study of animal behaviour.

But don’t neglect fieldwork! By casting their actual eyes and ears into the wild, researchers can understand the social structure and behavioural quirks of their animals—information that no collars can provide. The trick will be to marry that hard-won, old-fashioned knowledge with the world of big data. “That would be the dream,” says Strandburg-Peshkin.

“Most behavioural research on wild baboons requires years of study and yields very little data,” says Andrew King from Swansea University, who has done more work on baboons than most. “This study is an excellent example of how we can generate lots of data very quickly to complement long-term observational studies.”

“We are using similar tracking collars to understand baboon behaviour and ecology in Namibia and South Africa,” he adds. “The next few years will be a lot of fun.”

Reference: Strandburg-Peshkin, Farine, Couzin & Crofoot. 2015. Shared decision-making drives collective movement in wild baboons. Science http://dx.doi.org/10.1126/science.aaa5099

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Fish that Walks on Land Swallows With Tongue Made of Water

In the distant past, between 350 and 400 million years ago, a group of our fishy ancestors started crawling up on land. The fins that propelled them through the water gradually evolved into sturdy, weight-bearing limbs. Their hind legs connected directly to their hips, which became bigger. Swimming fish became walking, four-legged tetrapods, such as amphibians, reptiles, and mammals.

Scientists have studied the evolution of tetrapod limbs and skeletons in incredible detail, but other aspects of our invasion of land are less clear. How, for example, did our pioneering ancestors eat?

Many fish feed by sucking. As they open their jaws, a horseshoe-shaped bone called the hyoid pushes down on the floor of the mouth, expanding it, and creating a flow of water that draws prey inside. Even species that take bites and nibbles rely on a similar suction to swallow food once it’s inside their mouths.

This technique works because fish are constantly surrounded by water. It doesn’t work on dry land. Fortunately, tetrapods solve that problem with a muscular tongue, which helps to move food from the mouth to the throat. Once again, the hyoid is involved—it’s the bone that the tongue is attached to. But how did this structure evolve? How did the hyoid go from being a bone that creates suction to one that moves a tongue? How did the first tetrapods swallow?

These questions have been hard to answer because very few fossils of early tetrapods contain decent traces of the hyoid. But Krijn Michel from the University of Antwerp tried a different tactic: he studied a delightful fish called the Atlantic mudskipper. This tiny creature looks like a tiny doorstop with a pair of fins and googly eyes, and it lives throughout the mangrove swamps of eastern Africa, the Indian Ocean, and the western Pacific. It spends a surprising amount of time on land. It hauls itself about on its fins, fighting, mating, and foraging in the open air.

Michel filmed Atlantic mudskippers with high-speed cameras as they sucked up pieces of shrimp that had been placed on dry surfaces. As he reviewed the videos, he noticed something odd. In the moments after a mudskipper leans forward and opens its mouth, a small bubble of water protrudes from its open jaws. The water spreads over the morsel of food, which the mudskipper envelops with its mouth. It then sucks both morsel and water back up.

The water acts like a tongue—a “hydrodynamic tongue”, in Michel’s words. It allows the fish to lap up its food and then swallow it.

Michel showed how important the ‘tongue’ is by placing morsels of shrimp on an absorbent surface and filming the mudskippers with X-ray video cameras. This time, as the mudskippers leant in, their watery tongues were drained away. They could still grab the shrimp in their jaws but they couldn’t swallow. On 70 percent of their strikes, they had to return to water before they could gulp down their mouthfuls.

This explains why mudskippers almost always fill their mouths with water before they come out on land. By keeping that watery tongue, they can swallow several mouthfuls before having to return to the water. By contrast, the eel-catfish, which also ventures onto land but doesn’t use the same trick, must always return to water after it has grabbed its prey.

“These findings suggest that swallowing food in air may have been a substantial problem for the transition from water to land during vertebrate evolution,” says Beth Brainerd from Brown University. “When early tetrapods started feeding on land, they had to evolve a new way to move food to the back of the throat for swallowing.”

Did they use a watery tongue, a la mudskippers? Perhaps, but it’s important to remember that these are modern fish, and not tetrapods-in-the-making. Hundreds of millions of years of evolution separate them from our land-colonising ancestors. At most, they can hint at the kinds of strategies that early tetrapods might have used when they moved onto land.

A watery tongue, for example, could have provided a workable interim solution, allowing the animals to feed successfully while their hyoids changed and they developed muscular tongues. Indeed, when Michel trained his X-ray cameras on a fish and a newt, to watch how their hyoids moved when they ate, he found that the newt’s movements more closely resembled those of the mudskipper. The bone’s making the right sort of movements, even if there’s no muscular organ attached to it.

Reference: Michel, Heiss, Aerts & Van Wassenbergh. 2015. A fish that uses its hydrodynamic tongue to feed on land. Proc Roy Soc B  http://dx.doi.org/10.1098/rspb.2015.0057

PS: Fish do have “tongues” but the term is a loose parallel; unlike our muscular organs, these tongues (usually) can’t stick out of the mouth, and they don’t help with swallowing. They can, however, help with chewing.

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In Which I Visit a Penguin Experiment and Hilarity Ensues

A few months ago, I noticed a tweet from John Hutchinson, saying that he was going to London Zoo to study their penguins, and how they move. I’ve covered Hutchinson’s work before; it frequently involves ushering animals over force-plates. And since the animals in this case would be penguins, it was practically guaranteed that something amusing would happen. Because penguins. So, I tagged along, and then wrote about it for the New Yorker’s Elements blog. It’s my first piece for them. Here’s a taster:

The first penguin approached. With an agility that belied its bumbling demeanor, it leaped straight over the smaller force plates. The second penguin seemed more circumspect, pausing at length to examine the unfamiliar terrain. Matyasova lured it on with sprat, but a third penguin blundered forward, joining it on the large force plate—a four-footed, two-penguin chimera. Matyasova then tried putting a penguin directly on the plate: it stood still and pecked at the duct tape holding the corridor together. Fortunately, this was just a dry run, though it was clear that Hutchinson’s patience was being tested as much as his equipment. “It almost always takes a while for the animals to get used to what you want them to do,” he said. “They’ll get progressively more coöperative.”

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Cave-Exploring Snake Robot Gets Inspiration From Sidewinders

Three years ago, a robotic snake called Elizabeth slithered into Egyptian caves to search for long-hidden ships.

The caves lie on Egypt’s east coast, and contained the dismantled remnants of vessels that the Egyptians used to sail the Red Sea. They were discovered about a decade ago and some have surrendered their secrets with relative ease. Others, however, are too dangerous and unstable for people to explore.

Enter Elizabeth. The serpentine robot, built by Howie Choset at Carnegie Mellon University and named after his wife*, was designed to explore spaces that humans cannot. She can slide over rough terrain, slink through tight cracks, and manoeuvre around rubble. During her Egyptian field test, she performed beautifully, with one major exception: When the team tried to drive her up sandy slopes, she slipped and slid.

Real snakes face the same problem, and many desert-dwelling species have solved it through a bizarre technique called sidewinding. It’s a very counter-intuitive style of movement. From above, it looks like the snake is travelling sideways in a beautiful undulating wave. But it leaves behind a series of straight tracks, each the length of its body.

The trick to understanding the technique is to realise that the snake is never sliding. Instead, it is constantly picking itself off from its current position and laying itself down in a new spot. The head goes first, and the rest of the body follows. But before the body catches up completely, the head is off again. At any point of time, the snake is only touching the ground with two short parts of its body. That’s why it moves in a wave, but leaves a straight track.

Sidewinding is perfect for negotiating dunes. Rather than pushing against slippery sand, the snake’s rolling motion means that it’s mostly in static contact with its surface. Many species of snake can do this, but only two have truly mastered the technique—a rattlesnake from the US and Mexico, and a horned viper from Angola and Namibia. Confusingly, both are called sidewinders.

Choset’s robot Elizabeth could sidewind, but not very well. It was missing something that its real counterparts were doing.

Elizabeth, the robot snake. Credit: Nico Zevalios and Chaohui Gong.
Elizabeth, the robot snake. Credit: Nico Zevalios and Chaohui Gong.

To discover that mystery ingredient, Choset teamed up with Daniel Goldman from the Georgia Institute of Technology. For decades, Goldman has been fascinated by how animals move on and through sand. He has studied baby sea turtles as they clamber over a beach, and a pointy-nosed lizard called the sandfish as it swims through sand. And his team have built robots that emulate these animals, to reveal the physics behind their movements. Guy knows sand; guy knows robots. And as luck would have it, he was already starting to study sidewinders.

The team, led by postdoc Hamidreza Marvi and student Chaohui Gong, worked with six sidewinders (the American kind) from Zoo Atlanta. They put the snakes on a sandy trackway that could be inclined at different angles. They even trucked in sand from Arizona’s Yuma Desert to give the snakes material that they would normally face in the wild. “They’re excellent study subjects,” says Goldman. “They sidewind on command. Put them in a container and off they go.”

At first, the team assumed that as the track got steeper, the sidewinders would respond by digging their bodies more firmly into the ground, just like we would if we climbed a steep dune. They didn’t. Instead, they kept more of their body in contact with the ground, giving themselves more purchase on increasingly treacherous slopes. As the researchers raised the flat track to a 20 degree incline, the sidewinders compensated by laying down twice as much body.

The team also tested 13 other species of rattlesnake from Zoo Atlanta. None of them sidewind naturally, and none of them could negotiate the same slopes that the sidewinders could. They tried to climb straight up, and failed. “It was quite amusing,” says Goldman. “One of the comments we got from our reviewers was that it was obvious what the sidewinders do. Well, it wasn’t obvious to the other snakes!”

The team then programmed Elizabeth to mimic the sidewinders, and found that she suddenly became much better at moving up slopes. Her performance revealed that snakes have to stick within a certain range of contact lengths, and this range narrows as the slopes get steeper. If they don’t lay down enough body, they slip. If they lay down too much, they can’t lift the rest of themselves effectively, and run into the sand in front of them. They end up digging a hole, rather than making progress.

So, by playing with their robot, the team understood more about what the snakes do. And by studying the snakes, they improved their robot. “Using our understanding of fundamental engineering, we advanced these robots very far but we couldn’t get them up sandy hills,” says Choset. They only surmounted that final hurdle by studying nature.

Choset thinks that the snake-bots have many possible uses. They could search for survivors trapped in collapsed buildings. They could also inspect dangerous environments like nuclear storage facilities. And, of course, they could explore archaeological sites. “If we have the opportunity to return to Egypt, we’d use this capability,” he says. “Archaeology is like search and rescue except everyone’s been dead for thousands of years so there’s no rush.”

* Choset tells me that there was a second snake robot called Howard, but he was lost in some airline baggage mix-up. Samuel L. Jackson was unavailable for comment.

Reference: Marvi, Gong, Gravish, Astley, Travers, Hatton, Mendelson, Choset, Hu & Goldman. 2014. Sidewinding with minimal slip: Snake and robot ascent of sandy slopes. Science http://dx.doi.org/10.1126/science.1255718

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On The Evolution of Migration

Every autumn, the swallow may fly south with the sun. It is joined by the house martin, the plover, and hundreds of other species of birds. After spending the summer in temperate breeding grounds, where both daylight and food are plentiful, they head south before both resources fade in the winter. When spring returns, so do these migrants.

Their treks can be epic. The bar-tailed godwit flies from Alaska to New Zealand. The Arctic tern makes a 70,000 kilometre round-trip from one pole to another. Even less ambitious migrations still involve small birds, the size of your hand, crossing whole continents.

Migration evolved from stagnation. The ancestors of these birds stayed in the same place all-year round, and gradually, they shifted either their breeding grounds or their wintering ones. Most scientists believe that the former happened: that tropical birds gradually moved their breeding grounds north, either to chase a glut of summer food or to leave their competitors behind. But some think that the opposite happened: birds in temperate climates gradually moved south to escape the harsh winters.

Fossils would normally help to settle these competing explanations, but small songbirds have tiny, hollow bones that don’t fossilise very well. So, Benjamin Winger and Richard Ree from the University of the Chicago used a different approach. They built a mathematical model that uses the ranges of modern birds and their evolutionary relationships to reconstruct the historical ranges of their ancestors. It’s a tool for looking at geography, back through history.

They focused on New World emberizoids—an unfamiliar name for a group of extremely familiar songbirds including warblers, sparrows, blackbirds, orioles and tanagers. “They’re really familiar birds to birdwatchers and ornithologists,” says Winger (providing a great example of nominative determinism). “If you go out during spring migration, these are many of the birds you’ll see.”

Most of the emberizoids live in the tropical parts of the Americas, and stay there throughout the year. But they also include 120 species of migrants, which travel north in the spring to breed. At first glance, it looks like these birds originated in the tropics and gradually expanded north, supporting the dominant idea. But Winger and Ree found that the opposite scenario was more common. Their model told them that emberizoid migrants were twice as likely to evolve out of North America as out of the tropics.

The team also found that for many species, migration was a gateway drug for a permanent tropical existence. From an all-year life in the north, they started moving south in the winter, until some of their descendants just stayed in the tropics all the time.  They cashed in their return tickets for one-way passes and never went back.

“This is something that people have observed at a smaller scale,” says Winger. “The barn swallow is a nice example. They breed in North America and winter in the tropics, but there’s a population that has begun breeding in Argentina.”

Of course, this only tells us about how some birds evolved their long migrations, but not why they did so. That’s a topic for another study (and another post; although here’s a good primer). But Winger says the how is important. “There are many competing hypotheses for the evolutionary drivers of migration, but they rely on certain patterns of geographic change.” By better understanding how those patterns changed, he hopes to bring more clarity about why they did so.

“In some ways, it’s intuitive,” he adds. “The winter is a pretty harsh place to be, so birds that leave, or evolve the ability to leave, will go on to survive.”

Reference: Winger, Barker & Ree. 2014. Temperate origins of long-distance seasonal migration in New World songbirds. PNAS. http://dx.doi.org/10.1073/pnas.1405000111

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Why Octopus Arms Don’t Get Tangled

If you cut off an octopus’s arm, the severed limb will still move about for at least an hour. That’s because each arm has its own control system—a network of around 400,000 neurons that can guide its movements without any command from the creature’s brain.

The hundreds of suckers along each arm can also behave independently. If a sucker touches an object, it will change its shape to form a tight seal, and contract its muscles to create a powerful suction. It grabs and sucks, by reflex.

This setup allows the octopus to control its astonishing appendages without overly taxing its brain. Your arm has a small number of joints and can bend in a limited number of ways. But an octopus’s arm can create as many joints as it wants, in any direction, anywhere along its length. It can also extend, contract, and reshape itself. To control such infinitely flexible limbs, it needs to outsource control to the limbs themselves.

But what happens if one arm brushes past another? If the suckers grab objects on reflex, why aren’t octopuses constantly grabbing themselves by mistake?

To find out, octopus arm expert Benny Hochner teamed up with octopus sucker expert Frank Grasso.“Octopus suckers are undervalued in terms of their complexity,” says Grasso. “I’m one of their proponents. They’re really exquisite manipulation devices.”

Together with Nir Nesher and Guy Levy, the duo noticed that the suckers on a freshly amputated arm will never attach to another arm. Sure, they’ll grab skinned parts of an amputated arm or the bare flesh at the point of amputation, but not the arm itself. They’ll grab Petri dishes, but not those that are covered with octopus skin.

Common octopus. Credit: Pseudopanax.
Common octopus. Credit: Pseudopanax.

Octopuses clearly have some kind of sucker-proof coating on their own skin.  The team confirmed this idea by extracting chemicals from the skins of both fishes and octopuses, and applying these cocktails onto Petri dishes. They found that the octopus extract could block a sucker’s grabbing reflex but the fish extract could not.

“We all knew that octopuses are very dependent on chemical sensing but we haven’t done much research on this,” says Jennifer Mather from the University of Lethbridge, who studies octopus behaviour. “This paper will probably kick start it.”

Whatever the mystery chemical, it’s clear that octopuses can override its influence. The team showed that that living animals will occasionally grab amputated arms, even by the skin. Their brains can veto the reflexes of their suckers.

They can even tell if an amputated arm belonged to them or to another octopus. If they sensed another individual’s severed arm, they would often explore it, grab it, and hold it in their beaks in an unusual posture that the team called “spaghetti holding”. (Common octopuses will cannibalise their own kind, so a floating arm is fair game.) But when they sense their own severed limbs, they typically avoided it, and only rarely treated it like food.

“This gives us some idea of how octopuses might generate a sense of self—not by vision, which would be hopeless given their changeable appearance, but by chemical cues,” says Mather.

The octopus’s self-avoiding arms are a great example of embodied cognition—the idea that an animal’s body can influence its behaviour independently of its brain. As Andrew Wilson and Sabrina Golonka explain, “the brain is not the sole resource we have available to us to solve problems. Our bodies… do much of the work required to achieve our goals.”

The octopus… well… embodies this idea. Its brain governs many of its decisions and exerts control upon its arms, but the arms can do their own thing, including getting out of each others’ way. The animal doesn’t need to know the location of each of its arms to avoid embarrassing entanglements. It can let its arms do the work of evading each other.

This concept might be useful for designing robots. A typical robot, like Honda’s ASIMO, relies on top-down programs that control his every action. He can pull off pre-programmed feats like dancing or running, but he trips over even minor obstacles. He’s inflexible and inefficient. By contrast, Boston Dynamics’ Big Dog relies on embodied cognition. His springy legs are designed to react to rough terrain without needing new instructions from his central processor. (Thanks again to Wilson and Golonka for the examples.)

By studying the arms of octopuses, scientists may one day be able to design soft versions of Big Dog, pairing its flexible movements with an equally flexible chassis. Big Octopus, perhaps.

Reference: Nesher, Levy, Grasso & Hochner. 2014. Self-Recognition Mechanism between Skin and Suckers Prevents Octopus Arms from Interfering with Each Other. Current Biology. http://dx.doi.org/10.1016/j.cub.2014.04.024

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Homing Pythons Re-Enact Homeward Bound

In the Disney film Homeward Bound, two dogs and a cat undertake a perilous journey through the American wilderness to try and find their way home.

This story is the same but instead of pets, we have six giant snakes.

The Burmese python can grow up to 5.7 metres in length, making it one of the world’s largest snakes. As its name suggests, it hails from south-east Asia, but the exotic pet trade unleashed it upon the USA. Since 2000, these giants have spread across 1,000 square kilometres of Florida’s wetlands, suffocating local mammals and birds (and the odd alligator) along the way.

In 2006, Shannon Pittman from the University of Missouri-Columbia travelled to the Everglades National Park and implanted a dozen pythons with radio transmitters to track their movements. As part of that study, she put six of the snakes in sealed plastic containers, and drove them to locations 21 to 36 kilometres away before releasing them.

Pittman expected the snakes to randomly wander about their new environment. That is not what happened.

Instead, the pythons slithered home.

All of the them started moving towards the places where Pittman had originally captured them. Their accuracy was incredible. They stayed within 22 degrees of the right homeward bearing, and within 3 to 10 months, five of them had ended up within five kilometres of their original position.

This map shows their movements. Each colour represents a different snake. They were captured at the circles, taken to the triangles, and ended up at the diamonds. They all did spectacularly well. Even the blue snake seems to have headed in mostly the right direction before veering off for whatever reason.

Credit: Pittman et al, 2014.
Credit: Pittman et al, 2014.

Homing pythons!


Many animals, from pigeons to salmon to spiny lobsters, have incredible navigational skills, but this is the first time that any snake has demonstrated a similar acumen. They must have some sort of compass sense because they kept the right bearing, and they must have an internal map because they knew when they had reached the right destination.

For a compass, they could be picking up on the position of the sun or stars, the smell of home, or changes in the Earth’s magnetic field. As for the map, the snakes were always transported in sealed containers so they couldn’t memorise cues about their journeys as some animals do. They must be using some cues in their environment to work out their position but, again, we have no idea what those cues might be. (I would personally love it if they turned out to have a magnetic sense because I’ve written about such senses extensively—but really, who knows?)

Pittman suspects that this navigational prowess may have contributed to the Burmese python’s skill as an invader, allowing them to explore new terrain in confidence and expand their range more quickly. The discovery may also help scientists to better predict and control the snakes’ movements.

Reference: Pittman, Hart, Cherkiss, Snow, Fujisaki, Smith, Mazzott & Dorcas. 2014. Homing of invasive Burmese pythons in South Florida: evidence for a map and compass senses in snakes. Proc Roy Soc B http://dx.doi.org/10.1098/rsbl.2014.0040

Related: Invasive Pythons Can Find Home 20 Miles Away, Study Says

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Where Do Baby Turtles Go During Their Lost Years?

Never agree to write a turtle’s biography. You will, at one crucial point, run out of material.

Every sea turtle begins life in the same way. It hatches within its buried nest, forces its way to the surface, and sprints towards the water past a gauntlet of crabs, birds and other predators. Many die, but they emerge in such numbers that there are plenty of survivors. They dive beneath the waves… and disappear.

By the time Atlantic loggerhead turtles start showing up in coastal waters again, they’ve grown from palm-sized infants into large animals whose shells are a couple of feet long. They must have been away for several years, but their movements are secrets withheld by the vastness of the ocean. We know the beaches that the baby turtles hatch from and many of the sites where adults go to feed and breed, but their biographies are missing the all-important childhood chapters.

“It is easy to walk along a beach, counting nesting females or successful hatchlings,” says Katherine Mansfield from the University of Central Florida, who has studied turtles for over 20 years. “It is much harder to survey an entire ocean basin.”

Mansfield doesn’t have to. By fitting 17 newborn loggerheads with tiny satellite tags, she has tracked their movements and made a clear map of their so-called “lost years”.

Her team took a long time to perfect the tags, and tested them extensively in the lab to make sure that they would not interfere with the tiny babies. They couldn’t be too heavy, so the team used solar panels rather than clunky batteries. They couldn’t be too buoyant either. And most importantly, they had to stick for as long as possible. When the team used glue, the turtles’ shells grow so quickly that the tags all fell off within few weeks.

“We realized that the turtles’ shells are made of keratin—the same thing as human fingernails,” says Mansfield. “So, we contacted my collaborator’s manicurist and she suggested using an acrylic base coat to seal the shell from peeling.” Her idea worked. The tags finally stuck.

The team released the turtles off the south-east coast of Florida, and the tags tracked their movements for anywhere from 27 to 220 days.

Turtle-migrationsAt first, the babies all followed the Gulf Stream, the warm current that flows from the tip of Florida, past the eastern seaboard of the US, and across the Atlantic Ocean. They hugged the edge of the continent at first, but once they got past North Carolina, they left these predator-rich waters and headed eastwards into more open waters.  In just seven months, one of them swam as far as the Azores—more than 3,000 miles away—before its tag finally came off.

Some of this fits with what scientists had guessed, based on circumstantial evidence. Loggerheads that hatch in Florida clearly head north-east, since loggerheads in the eastern Atlantic are genetically linked to those that nest in the west, and also bigger.

Mansfield’s data also offered a few surprises. Most people assumed that the turtles stay within the North Atlantic Gyre—a set of powerful currents that circle clockwise around the Atlantic, and that include the Gulf Stream. That’s mostly right, but the turtles weren’t carving a fast or straight path across the Atlantic. Overall, they headed in the right direction, but they also spent a lot of time going in local circles. Some of these deviations took them out of the Gyre altogether, into the Sargasso Sea—an area in the middle of the Atlantic rich in floating Sargassum seaweed.

“The basic overall pattern of movement is similar to what has been proposed previously, but there is considerable variation in the individual paths that different turtles take,” says Ken Lohmann at the University of North Carolina, who studies the magnetic senses of turtles.

“The findings are consistent with recent models suggesting that young turtles are active navigators and do not simply drift passively with the currents,” he added. “They also support the idea that turtles use regional magnetic fields as open-ocean navigational markers, and correct their headings when they are in danger of swimming too far north or south.”

Mansfield also suggests that the turtles might have encountered a floating habitat, like Sargassum, and just stayed with it until they ended up in the Sargasso Sea. Sargassum is a good habitat for a baby turtle. Its brown fronds, branches and floats provide shelter from predators. They also absorb a lot of sunlight, warming the local water by six degrees over the surrounding ocean. Turtles are cold-blooded and could grow faster in warmer waters, reaching sexual maturity at an earlier age and outgrowing potential predators.

The turtles also spent most of their time near the ocean surface—another trait that would help to keep them warm.  Water is water to us. To a turtle, the seaweed-filled surface waters are the equivalent of luxury accommodation.

Mansfield now wants to study the lost years of other turtle species, including those from other oceans with different currents and scarce Sargassum. “There are so many questions that still need answering,” she says.

Reference: Mansfield, Wyneken, Porter & Luo. 2014. First satellite tracks of neonate sea turtles redefine the ‘lost years’ oceanic niche. http://dx.doi.org/10.1098/rspb.2013.3039