"An Immense World"

[fiefoe]

Ed Yong's latest book is chock-full of amazing animal facts and admirable scientists who found out about such things.

• The disc of stiff feathers on the owl’s face funnels sounds toward its sensitive ears, one of which is slightly higher than the other. Thanks to this asymmetry, the owl can pinpoint the source of the mouse’s skittering in both the vertical and horizontal planes.
• All of this commotion goes unnoticed by the spider, which barely hears or sees the participants. Its world is almost entirely defined by the vibrations coursing through its web—a self-made trap that acts as an extension of its senses.
• Earth teems with sights and textures, sounds and vibrations, smells and tastes, electric and magnetic fields. But every animal can only tap into a small fraction of reality’s fullness. Each is enclosed within its own unique sensory bubble, perceiving but a tiny sliver of an immense world.
• Rather, he treated the Umwelt concept as a unifying and leveling force. The human’s house might be bigger than the tick’s, with more windows overlooking a wider garden, but we are still stuck inside one, looking out. Our Umwelt is still limited; it just doesn’t feel that way. To us, it feels all-encompassing. It is all that we know, and so we easily mistake it for all there is to know. This is an illusion, and one that every animal shares.
• There are animals with eyes on their genitals, ears on their knees, noses on their limbs, and tongues all over their skin. Starfish see with the tips of their arms, and sea urchins with their entire bodies. The star-nosed mole feels around with its nose, while the manatee uses its lips.
• “They move finished and complete, gifted with extensions of the senses we have lost or never attained, living by voices we shall never hear,” wrote the American naturalist Henry Beston. “They are not brethren, they are not underlings; they are other nations, caught with ourselves in the net of life and time, fellow prisoners of the splendour and travail of the earth.”
• Senses always come at a cost. Animals have to keep the neurons of their sensory systems in a perpetual state of readiness so that they can fire when necessary. This is tiring work, like drawing a bow and holding it in place so that when the moment comes, an arrow can be shot.
• The Umwelt concept... But to me, the idea is wonderfully expansive. It tells us that all is not as it seems and that everything we experience is but a filtered version of everything that we could experience. It reminds us that there is light in darkness, noise in silence, richness in nothingness. It hints at flickers of the unfamiliar in the familiar, of the extraordinary in the everyday, of magnificence in mundanity.

• It means that whenever we exhale, we purge the odorants from our noses, causing our experience of smell to strobe and flicker. Dogs, by contrast, get a smoother experience, because odorants that enter their noses tend to stay there, and are merely replenished by every sniff.
• They could detect a single fingerprint that had been dabbed onto a microscope slide, then left on a rooftop and exposed to the elements for a week.
• When Finn sniffs, he is not merely assessing the present but also reading the past and divining the future. And he is reading biographies.
• People also excel at discriminating between smells. While it’s easy to find two colors that humans can’t tell apart, it’s very hard to find indistinguishable pairs of odors. Neuroscientist John McGann has tried, and tells me, “We tried odors that mice can’t tell apart and humans were like: No, we’ve got this.”
• Their signals can then be detected and exploited by bacteria-killing viruses, which have a chemical sense even though they are such simple entities that scientists disagree about whether they’re even alive. Chemicals, then, are the most ancient and universal source of sensory information.
• The variation among possible odorants is so wide that it might as well be infinite. To classify them, scientists use subjective concepts like intensity and pleasantness... Even worse, there are no good ways of predicting what a molecule smells like—or even if it smells at all—from its chemical structure. And yet, many animals naturally grapple with the intricacy of olfaction,... Their noses are kings of infinite space.
• a slightly different version of OR7D4, androstenone smells like vanilla. That’s just one receptor out of hundreds, and all exist in varied forms, bestowing every individual with their own subtly personalized Umwelt. Everyone likely smells the world in a slightly different way.
• Smell is so important to them that when scientists transplanted the antennae of female sphinx moths onto males, the recipients behaved like females, seeking out the scent of egg-laying sites instead of mates... But they only put this amazing sense toward a few specific tasks. Moths have been described as “odor-guided drones,” and that’s not an exaggeration. Many males don’t even have mouthparts when they reach adulthood.
• Ant pheromones are another story. There are many, and ants put them to different uses depending on their properties. Lightweight chemicals that easily rise into the air are used to summon mobs of workers that can rapidly overwhelm prey, or to raise fast-spreading alarms... Medium-weight chemicals that become airborne more slowly are used to mark trails.
• Female lobsters urinate into the faces of males to tempt them with a sex pheromone.
• It was astonishing that just one compound could so greatly affect the sex lives of so complex an animal. It was even more astonishing that female moths attract males with the same substance... Rasmussen eventually discovered that elephants can tell, through smell, when females are at different parts of their estrus cycles, or when bulls are in the hyperaggressive sexual state called musth. They can also identify individuals. As they walk the time-worn trails that connect their home ranges, they leave dung and urine behind—not waste, but personal stories to be read by the trunks of others around them.
• In the oceans, plankton release DMS when they’re eaten by krill—shrimp-like animals that are, in turn, eaten by whales, fish, and seabirds. DMS doesn’t dissolve easily in water, and eventually makes its way into the air. If it rises high enough, it seeds clouds... In particular, DMS is the scent of bountiful seas,
• Snake tongues come in shades of lipstick red, electric blue, and inky black... Schwenk tells me, still slightly outraged. “Someone who studied hummingbird nostril mites thought that what I did was funny!
• With the aid of its tongue, a snake smells the world. Each flick is the equivalent of a sniff. Indeed, the very first thing that a hatchling serpent does upon breaking out of its egg is to flick its tongue.
• It stabs the rodent with its fangs and injects venom. The toxins usually take a while to work, and since rodents have sharp teeth, the snake avoids injury by releasing its prey and letting it run off. After several minutes, it starts flicking its tongue to track down the now-dead victim. The venom helps. Aside from lethal toxins, rattlesnake venom also includes compounds called disintegrins, which aren’t toxic but react with a rodent’s tissues to release odorants. The snakes can use these aromas to distinguish envenomated rodents from healthy ones and to tell rodents envenomated by their own species from those bitten by other kinds of rattlesnakes. They can even track the specific individual that they attacked because they instantly learn the victim’s scent at the moment of a bite.
• Bill Ryerson, another of Schwenk’s students, analyzed those movements by getting snakes to tongue-flick into clouds of cornstarch... This motion creates two donut-shaped rings of continuously moving air that draw in odorants from the left and right sides of the snake. It’s as if the snake temporarily conjures up two large fans that suck in odors from either side,
• Taste is reflexive and innate, while smell is not... Odors, by contrast, “don’t carry meaning until you associate them with experiences,”... when the U.S. Army tried to develop a stink bomb for crowd control purposes, they couldn’t find a smell that was universally disgusting to all cultures.
• Taste, then, is the simpler sense... taste is almost always used to make binary decisions about food.
• The most extensive sense of taste in nature surely belongs to catfish. These fish are swimming tongues. They have taste buds spread all over their scale-free bodies,..  If you lick one of them, you’ll both simultaneously taste each other.
• small predatory dinosaurs probably lost the ability to taste sugar. They passed their restricted palate on to their descendants, the birds, many of which still have no sense for sweetness. Songbirds.. are an exception.
• This process is temporary: After the GPCRs are done, they either release or destroy the molecules that they’ve grabbed. But one group of them bucks this trend: opsins. They are special because they keep hold of their target molecules, and because those molecules absorb light. This is the entire basis of vision. This is how all animals see—using light-sensitive proteins that are actually modified chemical sensors. <> In a way, we see by smelling light.

• These tasks—sharp vision and motion detection—feel inseparable. And yet jumping spiders have separated them so thoroughly that they exist within different sets of eyes. The central ones recognize patterns and shapes and see in color. The secondary ones track movements and redirect attention.
• The Japanese yellow swallowtail butterfly has photoreceptors on its genitals. A male uses these cells to guide his penis over a female’s vagina, and a female uses them to position her egg-laying tube over the surface of a plant.
• ‘I think most of the carnivores are hunting at night, and their visual acuity is going to be so much worse than humans’. They probably can’t see the stripes.’... Our exceptionally sharp vision, Melin realized, gives us a rarefied view of a zebra’s stripes.
• Acute eyes also come with a hefty drawback. As the wedge-tailed eagle demonstrates, animals can achieve sharper vision by having smaller and more densely packed photoreceptors. But each receptor now collects light over a smaller area and is thus less sensitive. These qualities—sensitivity and resolution—seesaw against each other. No eye can excel at both...  (There are no nocturnal eagles.)
• Each one sits at the end of a mobile tentacle. Each has a little pupil: “It’s wild and creepy to see all of them opening and closing at the same time,” Speiser says. Light passes through the pupil and hits the back of the scallop’s eye, where it is reflected by a curved mirror. The mirror is a precisely tiled array of square crystals that collectively focus light onto the scallop’s retinas. That’s retinas, plural. There are two per eye, and they are about as different as two animal retinas could be.
• (scallop) knows when eyes in a certain region of its body have detected something, but it has no visual image of that object. It doesn’t experience a movie in its head the same way we do. It sees without scenes. <> This kind of vision is probably closer to our sense of touch than anything we experience with our eyes.
• A mallard duck’s visual field is completely panoramic, with no blind spot either above or behind it. When sitting on the surface of a lake, a mallard can see the entire sky without moving. When flying, it sees the world simultaneously moving toward it and away from it.
• To be more respectful of deep-sea Umwelten, Johnsen’s mentor Edith Widder created a stealth camera called Medusa. It films deep-sea animals with red light that most of them can’t see, and attracts them with a ring of blue LEDs that resemble a bioluminescent jellyfish. “The only real innovation is that we turned off the lights,” he says. “Once we do that, really big stuff shows up.”
• The largest toothed predators in the world, sperm whales are the giant squid’s main nemeses... They do not produce their own light, but just like a descending submersible, they trigger flashes of bioluminescence when they bump against small jellyfish, crustaceans, and other plankton. With its disproportionately large eyes, the giant squid can see these telltale shimmers from 130 yards away, giving it enough time to flee. It is the only creature with eyes large enough to see these bioluminescent clouds at a distance, and also the only one that needs to do so.

• And by collecting their poop and sequencing their DNA, she worked out which were trichromats and which were dichromats. Neither group, she found, is more likely to survive or reproduce than the other. The trichromats are indeed better at finding brightly colored fruit, but the dichromats surpass them at finding insects disguised as leaves and sticks.
• people who have lost their lenses to surgeries or accidents can perceive UV as whitish blue. This happened to the painter Claude Monet, who lost his left lens at the age of 82. He began seeing the UV light that reflects off water lilies, and started painting them as whitish blue instead of white.
• It’s very hard to detect movement with an eye that’s also moving. When we walk along a street or stare out a vehicle window, our eyes actually fix on specific points ahead of us, rapidly flicking from one to the next. These flicks, or saccades, are some of the fastest movements we make, which is just as well, because as they’re happening, our visual system shuts down. Our brains fill the millisecond-long gaps to create a sense of continuous vision, but that’s an illusion. The same thing happens to mantis shrimps when they do their slow midband scans... The jumping spiders we met in the previous chapter split different visual tasks—motion and colorful detail—among separate eyes. The mantis shrimps do the same among different portions of the same eye, and among different periods of time. To see movement, they have to give up color. To see color, they give up movement.
• It is formed when light is scattered by water or air, or when it reflects off smooth surfaces like glass, waxy leaves, or bodies of water. Humans are largely oblivious to polarization, but most insects, crustaceans, and cephalopods can see it in much the same way that they see color.
• Polarized light usually oscillates in a single fixed plane, but that plane can sometimes rotate, so the light travels along a twisting helix. This is called circular polarization. And as Marshall’s postdoc Tsyr-Huei Chiou found in 2008, mantis shrimps are the only animals that can see it... the only things in the mantis shrimps’ environment that reliably give off circularly polarized light…are the mantis shrimps themselves. One species reflects it from the large keel on its tail, which males use during courtship.
• They exploited it by slowly developing structures on their shells that reflect circularly polarized light, evolving signals that suited their eyes. This happens a lot. Signals are meant to be seen, and so the colors that adorn the fur, scales, feathers, and exoskeletons of animals are shaped by the colors that the animals’ eyes can perceive. In viewing nature’s paintings, eyes define its palette. <> Primates, for example, evolved trichromacy to better spot young leaves and ripe fruits. And once they added red to their Umwelt, they began evolving patches of bare skin that could convey messages by flushing with blood. The red faces of rhesus macaques, the red rumps of mandrills, and the comically red and bald heads of uakaris are all sexual signals made possible by trichromatic vision.
• Most of the fish in coral reefs are also trichromats. But since red light is strongly absorbed by water, their sensitivities are shifted toward the blue end of the spectrum. This explains why so many reef fish, like the blue tang that stars in Pixar’s Finding Dory, are blue and yellow. To their version of trichromacy, yellow disappears against corals, and blue blends in with the water. Their colors look incredibly conspicuous to snorkeling humans
• Cummings and Maan showed that you can work out who those predators are—in this case, birds—by studying the colors of their prey. Since eyes define nature’s palette, an animal’s palette tells you whose eyes it is trying to catch.
• I find these connections profound, in a way that makes me think differently about the act of sensing itself. Sensing can feel passive, as if eyes and other sense organs were intake valves through which animals absorb and receive the stimuli around them. But over time, the simple act of seeing recolors the world. Guided by evolution, eyes are living paintbrushes.

• In their wild burrows, naked mole-rats also sleep in large huddled piles to keep warm. Those at the bottom rapidly run out of oxygen, which is probably why they have evolved to withstand the gas’s absence. They’ve also been forced to tolerate carbon dioxide, which builds up in the nesting chambers with every exhalation.
• Nociception is the sensory process by which we detect damage. Pain is the suffering that ensues. Last week, when I accidentally touched a hot pan, the nociceptors in my skin sensed the scalding temperatures. That’s nociception, which triggered a reflex that forced my arm to withdraw before I realized what was happening.
• Appel found that they will nonetheless evacuate if given a small electric shock. These flights looked reflexive, but the crabs didn’t always flee. It took a stronger shock to force them out of their favored periwinkle shells than it did to evict them from the less desirable flat-top shells. And they were half as likely to abandon their shells if they could smell the scent of predators in the water. “That told me that this isn’t a reflex,”
• Crook found that injured squid behave as if their entire bodies were sore... Body-wide sensitivity also makes sense for animals that cannot physically reach most of their bodies...
• Octopuses are different. Unlike squid, they can touch every part of their bodies. They can even reach inside themselves to groom their own gills—the equivalent of a human putting a hand down their throat to scratch their lungs.

• The fly can tell if one antenna is just 0.1°C hotter than the other, and uses those comparisons to steer toward the more comfortable temperature. When Gallio tells me about these results, I suddenly reconsider the movements of every fly I’ve ever seen. Their paths, which always seemed so random and chaotic, now take on an air of purpose, as if the insect is threading its way through an obstacle course of hot and cold that I can’t perceive
• The fire-chasing Melanophila beetles, however, are drawn to heat... Arriving at a fire, the beetles have perhaps the most dramatic sex in the animal kingdom, mating as a forest burns around them. Later, the females lay their eggs on charred, cooled bark. When the wood-eating grubs hatch, they find an Eden. The trees they devour are too injured to defend against insect larvae feeding within them. The predators that might eat them are put off by the smoke and heat emitted from the embers and ashes. In peace, they thrive, mature, and eventually fly off in search of their own blazes. But forest fires are rare and unpredictable, and the beetles must have some means of detecting them from afar.
• Below their wings and just behind their middle legs, these insects have a pair of pits. Each one contains a cluster of around 70 spheres that together look like a malformed raspberry...these spheres under a microscope, he saw that each is filled with fluid and encloses the tip of a pressure-sensitive neuron. When infrared radiation hits the spheres, the fluid inside them heats up and expands. It can’t bulge outward because the spheres have hard exteriors, so instead it squeezes the nerves, causing them to fire... The beetles’ spherical sensors must be extraordinarily sensitive, since the insects frequently travel to burning forests and other hot places from dozens of miles away.
• Australia, though. There, three other types of insects independently evolved infrared sensors that allow them to exploit the tranquil paradise of a charred forest. Fire-chasing is a trick so useful that it has evolved at least four times over.
• Blood, after all, is a superb source of food—rich in nutrients, well balanced, and usually sterile. It’s no surprise that at least 14,000 animal species have evolved to feed on it, or that many of these—bedbugs, mosquitoes, tsetse flies, and assassin bugs—are attuned to heat.

• Sea otters have neither the large heat-retaining bodies nor the insulating blubber of seals, whales, and manatees. They do have the densest fur in the animal kingdom, with more hairs per square centimeter than humans have on our heads, but even that isn’t enough to stop heat from rapidly bleeding off their bodies. To stay warm, they need to eat a quarter of their own weight every day; hence their frenetic nature
• Hard-shelled prey nestle among the similar hard rocks, but in a split second, the otter feels the difference between the two, and pulls the former from the latter. With its sense of touch, its dexterous paws, and its overabundant mustelid confidence, it snatches that clam, yanks that abalone, grabs that sea urchin, and finally ascends to eat its catches, breaking the water at the end of this sentence.
• In one experiment, people could distinguish between two silicon wafers that differed only in their topmost layer of molecules, telling them apart thanks to minuscule differences in the way their fingers slid over the two surfaces.
• the mole can identify its prey, swallow it, and begin searching for the next mouthful in an average of 230 milliseconds and as little as 120 milliseconds. That’s as fast as a human blink.
• “it can make maps of what it touches,” Grant tells me. The information that builds those maps must flicker in and out as the whisker tips move. But Grant says that a mouse’s brain probably interprets these discrete touches in a seamless way. I wonder if whisking for them is like vision for us—an experience that feels uninterrupted even though our eyes are constantly darting and blinking.
• with the bit between his upper lip and nostrils. This large area, known as the oral disk, gives manatees the hangdog expression that makes them so endearing... The disk is muscular and prehensile, more like an elephant’s trunk than a typical lip. By flexing and flaring the oral disk, a manatee can handle and investigate objects with the same dexterity and sensitivity as a hand.
• Hugh and Buffett could use their body whiskers to detect the minute vibrations of a sphere that was shaking in the water. The animals were blindfolded, their facial whiskers were covered, and the sphere was positioned a meter away from their flanks. They sensed it nonetheless, even when it was displacing the water by less than a millionth of a meter.
• The disturbances created by moving underwater objects ought to die away so quickly that beyond a range of a few inches, they would be undetectable. But hydrodynamic wakes can actually persist for several minutes. Dehnhardt estimated that a swimming herring should leave a trail that a harbor seal could follow from up to almost 200 yards away.
• As a seal swims, its whiskers should produce their own swirling vortices of water... But harbor seals have an answer to this problem... Looking closely at his whiskers, I can see that they’re slightly flattened and angled so that the bladed edge always cuts into the water... the “beads” are part of the whiskers’ actual structure. They have an undulating surface that repeatedly widens and narrows along their entire length. The Rostock team showed that these shapes dramatically reduce the vortices left by the whiskers themselves.
• A swimming fish displaces the water in front of it, creating a flow field that envelops its body. Obstacles distort that field, and the lateral line can detect those distortions, providing the fish with a hydrodynamic awareness of its surroundings. If it swims toward an aquarium wall, the wall “prevents the water particles giving way as freely as in unobstructed water,”
• Each fish only attends to the small volume of water around it, but the sense of touch connects them all and allows them to act as a coordinated whole. Blind fish can still school.
• While most catfish have expanded their taste buds to cover their bodies, this cave species has done the same with its teeth, turning them into a body-wide coat of flow sensors... Those raging currents, she thinks, might have overwhelmed the lateral line, forcing the fish to evolve stiffer sensors. They now use their skin-teeth to find calm zones
• Bird flight looks so effortless that it’s easy to forget just how demanding it is. To stay aloft, birds continuously adjust the shape and angle of their wings. If they get everything right, air flows smoothly over the contours of each wing, producing lift. But if they hold their wings at too steep an angle, the smooth flows form turbulent vortices and the lift disappears. This is called stalling, and if the bird can’t avoid or correct it, it will drop out of the sky. This rarely happens, in part because filoplumes provide birds with the information they need to rapidly adjust their wings and stay in the air.
• The filiform hairs of crickets and the trichobothria of spiders are almost inconceivably sensitive. They can be deflected by a fraction of the energy in a single photon—the smallest possible quantity of visible light. These hairs are a hundred times more sensitive than any visual receptor that exists, or could possibly exist. Indeed, the amount of energy needed to shift a cricket’s hairs is very close to thermal noise—the kinetic energy of jiggling molecules... But the cricket hairs are a rare example of maximization, he says. “They almost couldn’t be better than they are, and that’s surprising.

• In the air, an animal’s pitch is normally tied to its size, which is why mice don’t bellow and elephants don’t squeak. That constraint doesn’t exist for surface waves, so small animals can make low-frequency vibrations that seem like they’re coming from much larger bodies... Airborne sounds have another limitation: They radiate outward in three dimensions, and so lose energy very quickly. Insects compensate for this by concentrating all their efforts in a narrow range of frequencies, producing simple chirps.
• Its sensors lie in its feet. On the joint that could be loosely described as an “ankle,” there’s a cluster of eight slits, as if the exoskeleton had been scored by a sharp knife. These are the slit sensilla—vibration-detecting organs common to all arachnids. Each slit is spanned by a membrane and connected to a nerve cell. When a surface wave reaches the scorpion, the rising sand pushes against its feet. This compresses the slits by an infinitesimal amount, but enough to squeeze the membrane and cause the nerves to fire. By sensing the tiniest changes in its own exoskeleton, the scorpion can feel the steps of passing prey.
• But the ancient bone-conduction pathway still works: Vibrations can pass directly to the inner ear via the bones of the skull, bypassing the outer ear and eardrum altogether... bone-conduction headphones... which is why people often think they sound strange on recordings. Those recordings reproduce the airborne components of our voices, but not the vibrations traveling through our skulls.
• Cats, for example, have a lot of vibration-sensitive mechanoreceptors in the muscles of their bellies. When a cat crouches down during a stalk, is it doing more than lying low? Is it also sensing the vibrations of potential prey?
• These spiders construct the surfaces that they then sense vibrations through. For that reason, the orb web isn’t just another substrate, like soil, sand, or plant stems. It is built by the spider and it is part of the spider. It is as much a part of the creature’s sensory system as the slits on its body.
• This dependency on vibrations is so absolute that many animals can exploit orb-weavers by camouflaging their footsteps. The small dewdrop spider Argyrodes is a thief, stealing from larger spiders like Nephila by hacking their webs. From a nearby hiding place, it runs several lines of silk over to the hub and spokes of a Nephila web, effectively plugging its sensory system into that of the bigger spider...  It also holds on to any strands it cuts to avoid any sudden releases in tension. Through such subterfuge, this thief is almost never caught. As many as 40 of them might be plugged into a single Nephila web.
• An orb-weaver not only builds its own vibrational landscape but also can adjust it as if tuning a musical instrument. The range of that instrument is immense... A spider can theoretically change the speed and strength of those vibrations by altering the stiffness of its silk, the tension in the strands, and the overall shape of the web.

• They act like a radar dish that collects incoming sound waves and funnels them toward the ear holes. These enormous openings are found behind the owl’s eyes, hidden among its feathers. In some species, they’re so wide that if you part the overlying feathers and look into the ears, you can see the back of the owl’s eyeball.
• An owl’s ears, however, are uniquely asymmetric, with the left being higher than the right... The owl’s brain uses these differences in timing and loudness to work out the position of a sound’s source in both the vertical and horizontal.
• the first insects were deaf. They had to evolve ears, and over their 480-million-year history, they did so on at least 19 independent occasions, and on almost every imaginable body part. Ears exist on the knees of crickets and katydids, the abdomens of locusts and cicadas, and the mouths of hawkmoths. Mosquitoes hear with their antennae. Monarch caterpillars hear with a pair of hairs on their midsection. The bladder grasshopper has six pairs of ears running down its abdomen, while mantises have a single cyclopean ear in the middle of their chests.
• Courting males might call 5,000 times in a single evening before they’re chosen. Ryan knows this because he spent 186 consecutive nights at Barro Colorado, recording the serenades and escapades of a thousand individually marked túngara frogs from dusk to dawn. It was a marathon of voyeurism, from which he learned one crucial fact: Chucks are very sexy... Courting males might call 5,000 times in a single evening before they’re chosen. Ryan knows this because he spent 186 consecutive nights at Barro Colorado, recording the serenades and escapades of a thousand individually marked túngara frogs from dusk to dawn. It was a marathon of voyeurism, from which he learned one crucial fact: Chucks are very sexy.
• Dooling found that humans could only distinguish between these sounds if the chunks were longer than 3 to 4 milliseconds. Canaries and budgerigars hit their limit at between 1 and 2 milliseconds. And zebra finches weren’t even slightly duped by the shortest 1-millisecond chunks.
• They completely shuffled the order of the syllables—C-E-D-A-B. The finches still couldn’t discriminate between them. The two sequences are patently different, but not different in a way that matters to the finches... “they don’t give a crap about the sequences,” Dooling says. “They care about what’s inside the individual notes.”
• The communication barrier between species is also a sensory one. Birds encode meaning in aspects of their songs that our ears can’t pick out and our brains don’t pay attention to.
• animal ears become more adept at discriminating between similar frequencies if their neurons integrate sound information over longer periods of time. But in doing so, they also become less sensitive to fast changes that occur within those periods. We saw a similar trade-off in the chapter on vision: Eyes can have exceptional resolution or exceptional sensitivity, but not both. Likewise, ears can have exceptional temporal resolution or exceptional pitch sensitivity, but not both.
• At that time, the birds need to parse all the information encoded within the fine structure of their calls, so their hearing needs to be as fast as possible—and it is. Lucas found that in the fall, their temporal resolution goes up, but their pitch sensitivity goes down.
• Knowing that fin whales also produce infrasound, Payne calculated, to his shock, that their calls could conceivably travel for 13,000 miles. No ocean is that wide... Clark calculated that one individual was 1,500 miles from the sensor that recorded it.
• Those songs might have other uses, too. Their notes can last for several seconds, with wavelengths as long as a football field. Clark once asked a Navy friend what he could do with such a call. “I could illuminate the ocean,” the friend replied. That is, he could map distant underwater landscapes,.. He also suspects that the animals can build up such maps over their long lives, accruing sound-based memories that lurk in their mind’s ear.
• If a whale hears the song of another whale from a distance of 1,500 miles, it’s really listening back in time by about half an hour, like an astronomer gazing upon the ancient light of a distant star...  When he thinks about whales, the world feels bigger, stretching out in space and time.
• Krill aren’t evenly distributed across the oceans, so to sustain their large bodies, blue whales must migrate over long distances. The same giant proportions that force them to undergo these long journeys also equip them with the means to do so—the ability to make and hear sounds that are lower, louder, and more far-reaching than those of other animals.
• the team showed that African elephants use infrasound just like their Asian counterparts—and in every conceivable context. There are contact rumbles that help individuals find each other.
• Hummingbirds eat insects as well as nectar, so perhaps they produce ultrasonic calls that they can’t hear to flush out the insects that can.

• Since we rarely see bats, it’s easy to mistake them for ecological B-listers that dine on the nocturnal scraps that birds leave behind. It’s actually the other way round: In some rainforests, bats devour twice as many insects as birds.
• The bat’s call is scattered and reflected by whatever’s around it, and the animal detects and interprets the portion that rebounds. But to successfully do this, a bat must cope with many challenges. I count at least 10. <> First, distance is an issue... Even the so-called whispering bats, which are meant to be quiet, will emit 110-decibel shrieks, comparable to chainsaws and leaf blowers. These are among the loudest sounds of any land animal.
• Bats fly so quickly that they must update those snapshots regularly to detect fast-approaching obstacles or fast-escaping prey. John Ratcliffe showed that they do so with vocal muscles that can contract up to 200 times a second—the fastest speeds of any mammalian muscle.
• They also space their calls, so that each goes out only after the echo from the preceding one has returned. The air between a big brown bat and its target is only ever filled by a call or an echo, and never both... the bat’s nervous system is so sensitive that it can detect differences in echo delay of just one or two millionths of a second, which translates to a physical distance of less than a millimeter.
• they account for one in every five mammal species. There are bats that pluck insects from the air and bats that pluck fruit from trees. There are bats that catch frogs, bats that drink blood, and bats that sip nectar with tongues more than twice as long as their bodies. There are bat-eating bats. There are bats that go fishing by echolocating on ripples. There are bats that pollinate plants by echolocating on dish-shaped leaves that are adapted to reflect sonar pulses.
• Their brief sonar pulses are separated by long gaps, so an FM bat has to get very lucky to hit an insect’s wing at exactly the right moment to return a glint. By contrast, the pulses of CF bats are long enough to cover an entire wingbeat. They catch glints galore.
• CF bats can compensate for Doppler shifts. When closing in on a target, they produce calls that are lower than their normal resting frequency, so the upshifted echoes hit their ears at exactly the right pitch... They can even do this for several targets simultaneously.
• Tiger moths, a diverse group of 11,000 species, have a pair of drum-like organs on their flanks. These vibrate to produce ultrasonic clicks that seem to baffle bats, causing them to miss the moths.
• The sperm whale—the biggest odontocete of all—does something even stranger. Its titanic barrel of a nose can make up a third of its 52-foot body, and the phonic lips lie at the very front. When they vibrate, most of their sound goes backward through the whale’s head. It passes through a fat-filled organ called the spermaceti (the contents of which whalers once prized), bounces off an air sac at the back of the head, and then moves forward through another fatty organ called the junk (which whalers deemed worthless). The sound that emerges from this absurd detour is the loudest in the animal world. At 236 decibels, it’s basically an explosion. When scientists want to calibrate hydrophones to record sperm whale clicks, they throw cherry bombs into the water.
• The dolphins were using sound to spot tennis balls across the length of a football field, in the underwater equivalent of a rock concert... It can almost certainly tell different species apart based on the shape of those air bladders. And it can tell if a fish has something weird inside it, like a metal hook. In Hawaii, false killer whales often pluck tuna off fishing lines

• Indeed, electric fish evolved their unique powers by modifying their own muscles or nerves into special electric organs. These organs consist of cells called electrocytes, stacked together like towers of pancakes flipped on their sides. By controlling the flow of charged particles called ions through an electrocyte, a fish can create a small voltage across it. And by lining these cells up and triggering them together, it can combine the minuscule voltages into substantial ones.
• They are also sensitive to salinity. In the Amazon basin, where many knifefishes live, heavy rainfall regularly flushes ions out of the water. Against this desalinated background, the conductive, salt-filled bodies of other animals pop out to fish that can electrolocate.
• Almost all other senses depend on stimuli that move. Odor molecules, sound waves, surface vibrations, and even light must all make journeys from sources to receivers. But whenever a knifefish fires its electric organ, electric fields immediately materialize around it... Electrolocation is an instantaneous sense.
• To double the range of its electric sense, it would have to expend eight times more energy—and it already spends a quarter of its total calories on generating its fields... With their awareness mostly confined to a small sensory bubble, they must quickly react to whatever they detect... This is another example of the intimate connections between an animal’s body and its sensory systems. The black ghost knifefish’s agility wouldn’t be much use without its wraparound electric sense, and its sense would be of little use if the fish weren’t so agile.
• The electric sense evolved from the lateral line. Electroreceptors grow from the same embryonic tissues that create the lateral line, and both sense organs contain the same kinds of sensory hair cells (which are also found in your inner ear).
• They are sensitive not only to conductance, which is an object’s ability to carry a current, but also to capacitance, which is its ability to store a charge. And in natural environments, “capacitance is a mark of the living,”
• These devices have revealed that fish use electric fields not just to sense their environment but also to communicate. They court mates, claim territory, and settle fights with electric signals in the same way other animals might use colors or songs.
• The neuroscientist Ted Bullock once showed that the black ghost’s electric field usually oscillates once every 0.001 seconds, with an error of just 0.00000014 seconds. It’s one of the most accurate clocks in the natural world.
• it’s as if the mormyrins have the electric version of color vision, while other elephantfishes are stuck with monochrome. <> Carlson suspects that these changes were triggered by a shift in the fishes’ social lives... These fish have diversified their electric signals 10 times faster than other elephantfishes and given rise to new species at three to five times the rate seen elsewhere.
• Animal bodies, then, are living batteries, producing bioelectric fields through the mere act of existing. These fields are thousands of times fainter than those produced by even weakly electric fish.
• Stephen Kajiura showed that a small species of hammerhead can detect an electric field of just one nanovolt—a billionth of a volt—across a centimeter of water... The undersides of their “hammers” are loaded with ampullae, and the sharks use these as one might use metal detectors, sweeping them over the seafloor in search of buried (edible) riches.
• The knifefishes and elephantfishes are special cases. On opposite sides of the world, they independently and successively evolved three kinds of electroreceptors: first, for passively detecting the electric fields of other fish; then, for actively sensing their own self-made fields; and finally, for detecting the fields of other electric fish.[*30] The history of these two groups is a spectacular example of convergent evolution, where two different groups of organisms accidentally show up at life’s party in the same outfits.
• They only work when immersed in a conductive medium. Water certainly counts, and it’s no coincidence that almost every electroreceptive animal we’ve met so far is aquatic.
• every day, around 40,000 thunderstorms crackle around the world. Collectively, they turn Earth’s atmosphere into a giant electric circuit. Whenever lightning strikes the ground, electric charge moves upward, so the upper atmosphere ends up with a positive charge and the planet’s surface with a negative one. This is the atmospheric potential gradient—a strong electric field that stretches from sky to ground. Even on calm, sunny days, the air carries a voltage of around 100 volts for every meter off the ground.
• Flowers, being full of water, are electrically grounded, and bear the same negative charge as the soil from which they sprout. Bees, meanwhile, build up positive charges as they fly, possibly because electrons are torn from their surface when they collide with dust and other small particles. When positively charged bees arrive at negatively charged flowers, sparks don’t fly, but pollen does.
• Alongside the bright colors that we can see (and the ultraviolet ones we cannot), flowers are also surrounded by invisible electric halos. And bumblebees can sense these.
• He found that spiders can sense Earth’s electric field and ride it... Spider silk picks up a negative charge as it leaves a spider’s body, and is repelled by the negatively charged plants on which they sit. That force, though tiny, is enough to launch the spider into the air. And since the electric fields around plants are strongest at points and edges, spiders can ensure a vigorous takeoff by ballooning from twigs and blades of grass.
• A striking pattern emerged: On days with the most intense solar storms, gray whales were four times more likely to beach themselves.
• He had signed up for a two-year project, and “my main concern was what I would do for the second year,” he tells me. “That was over 30 years ago. The only part I got right was that they have a magnetic sense.” He didn’t realize that they have two... Both inclination and intensity vary around the globe, and most spots in the ocean have a unique combination of the two. Together, they act like coordinates, much like latitude and longitude. They allow the geomagnetic field to act as an oceanic map. And turtles, as Lohmann found, can read that map.
• For this reason, most of the species that convincingly have a map sense use it to travel over long distances. <> Some songbirds recognize magnetic signposts on their migration routes, just as turtle hatchlings do.
• magnetoreception remains the only sense without a known sensor. Magnetoreceptors are “the holy grail of sensory biology,”
• He noted that a bird’s inner ear contains three canals full of conductive fluid. As a bird flies, the geomagnetic field could theoretically induce a detectable voltage in that fluid. Almost 130 years later, David Keays confirmed that he was right. Moreover, he found that these birds have the same protein in their inner ears that sharks use to sense electric fields.
• Schulten realized that if magnetoreceptors depend on radical pairs, then they can’t be found anywhere in an animal’s body. Instead, they’re probably in the organs best suited to collecting light. A songbird’s compass, he suggested, lies in its eyes. This idea lay fallow until 1998, when Schulten read about a new discovery. A group of molecules called cryptochromes, which were thought to only exist in animal brains, had also been found in their eyes. “I just fell off my chair,” Schulten told me, because he remembered that cryptochromes can form radical pairs with partner molecules called flavins.
• Animals might have to keep a running average of the signals from their magnetoreceptors over long periods of time. This limitation makes magnetoreception slow, cumbersome, and deeply paradoxical. It detects one of the most pervasive and reliable stimuli on the planet—the geomagnetic field—but does so in an inherently unreliable way.

• Whenever an animal moves, it unconsciously creates a mirror version of its own will, which it uses to predict the sensory consequences of its actions. With every action, the senses are forewarned about what to expect and can prepare themselves accordingly.
• Distinguishing self from other isn’t a given; it’s a difficult problem that nervous systems have to solve. “This is largely what sentience is,” neuroscientist Michael Hendricks tells me. “And perhaps it’s why sentience is: It’s the process of sorting perceptual experiences into self-generated and other-generated.”
• But as philosopher Peter Godfrey-Smith wrote in Other Minds, an octopus has “a body of pure possibility.” Aside from its hard beak, it is soft, malleable, and free to contort... The question turns out to be irrelevant. The brain doesn’t have to. It can mostly let the arms sort themselves out