(Burrowing Owl Update Below)
Ed Yong is the author of I Contain Multitudes: the Microbes Within Us and a Grander View of Life (2016), a book that peered intensely inside us and other living things to discover the myriads of bacteria, viruses, and other microscopic species that colonize us and live in symbiosis with us. He now brings his rare talent of jargon-free science writing to an outer world, specifically the slivers of the environment that our sensory equipment allows us to perceive. By “us,” he means a vast range of mammals, birds, reptiles, amphibians, fish, and insects, many of which can perceive things that are far outside the range of human perception. Following an older zoologist’s nomenclature, Yong calls this specific sensory envelope the creature’s Umwelt.
Every Umwelt is a filter. It excludes from the great noise of stimuli that surrounds us everything except that which the creature needs to survive and thrive. So, the tick doesn’t see colors or hear sounds; it only senses body heat, the touch of hair, and the gases that emanate from skin. We can’t see infrared radiation that many animals can detect, nor the ultraviolet light that’s essential to the worlds of birds and bees.
Some of these features, such as the keen odor sense of dogs, have been known since antiquity. A huge amount of knowledge about animal senses is new. Ongoing research using equipment unavailable a couple of decades ago is discovering animal sense perceptions that challenge our imaginations. Yong does a great job along the way introducing us to scientists who are doing the work. He’s also often funny.
The first step along the journey is to dump Aristotle’s five distinct senses, and five only: sight, hearing, smell, taste, touch. Many animals mix those up, seeing without eyes, hearing without ears, blending smell, taste and touch into the same organs. And many operate with senses that Aristotle could not imagine: such as electric fields and the magnetic fields of the earth.
Yong’s first chapter, titled “Leaking Bags of Chemicals,” is on the senses of smell and taste. He starts with the relatively well known, a dog’s sense of smell, which is legendary. Yet other animals, including rats, pigs, and elephants, are also excellent sniffers, and humans, contrary to myth, outperform dogs on a number of smell tests. Many human hunting-gathering groups have extensive smell vocabularies and rely on smell for survival. And then there is the puzzle of bacteria and viruses, which have no noses, but leave chemical trails and can follow the chemical trails of others. Smell is a chemical sense, and noses are not required equipment. Male sphinx months pick up sexual odors released by females miles away using feathery antennae. Ants also smell with their antennae, navigating in a complex set of smelly substances — pheromones — that govern an ant’s identity, its hive allegiance, its current task, and much else. Smell is at the core of ants’ sophisticated societies. The whole animal kingdom issues sexual pheromones in great clouds of a millionth of a gram that travel for distances. The champion smellers among mammals are elephants. They outperform highly trained dogs in chemical detection tasks. Their long and flexible trunks give them access to odors at many levels and their brains contain a huge olfactory processing center. What about birds? Since Aristotle, scholars knew that vultures had a keen sense of smell. Then along came John James Audubon, the bird painter, insisting this was all wrong. Through a series of bizarre experiments he maintained that vultures had no sense of smell and found their prey by sight alone. This remained ornithological textbook gospel for decades and the study of avian smell fell into neglect. Then Betsy Bang, a researcher and artist in the 1960s, noticed in the dissected beaks of a number of birds a set of cavities very similar to dogs’ which could have no other purpose but to smell. She also measured their olfactory bulbs and found they were especially large in turkey vultures and a number of other species, including tubenoses, long-distance sea birds such as albatrosses. She took on the fight with the legacy of Audubon, and soon found allies, such as Bernice Wenzel, one of the few female physiology professors in the U.S. at the time, and Gabrielle Nevitt, who was interested in tubenoses. It was Wenzel who discovered the role of dimethyl sulfate (DMS), a gas produced in the sea by plankton when eaten by krill. DMS is the single olfactory magnet that attracts tubenoses from many miles away on the high seas. It is for them not only a dinner bell but a relatively stable map of the oceans that they use to navigate. Visually the surface of the sea looks much the same, but to the bird’s nose, it has rich and distinctive features. Yong doesn’t drive the point home, but we know today that Audubon was dead wrong about birds’ sense of smell generally, and about turkey vultures particularly; they have an excellent sense of smell. Smell is also key to navigation for the snake. Its forked tongue collects odor molecules from both sides of the path ahead and transports them to sensors in the roof of its mouth, directly connected to its brain. The forked tongue lets the snake smell in stereo. The spots that the tongue contacts in the mouth are the vomeronasal organ. The snake’s regular nose, by contrast, has little to do. Many other animals, including elephants, horses, and cats, still have a vomeronasal organ in addition to a conventional nose. It isn’t clear why. Taste is obviously similar to but also dependent on smell. Some tastes, such as bitter, are said to be inborn and universal, while smell requires linkage with experience and culture to be evaluated. There are just five taste receptors in humans (salt, sweet, bitter, sour, umami) but an infinity of smells. Many insects taste with their feet. Others have taste receptors on other organs. Catfish have taste receptors all over their bodies and are basically “swimming tongues.” Most vertebrates don’t have taste buds for sweet. They can’t taste sugar and so don’t crave it. Many birds, by contrast crave all the bounty of sweetness that nature may offer.
Seeing forms the topic of Yong’s second chapter. The dazzling diversity of the smell chapter now seems like just a warmup for vision. We first meet a jumping spider, which has four pairs of eyes, each with different functions. The main pair discerns shapes, two others only detect motion. Their brains are the size of a poppy seed but they follow humans with their eyes and are clever at planning strategies to capture their insect prey. There exists a dizzying array of different kinds of eyes with different functions. At the base of them all is a cell, called a photoreceptor, which contains two partner molecules. When a photon strikes one of these molecules, it snaps into a different shape, compelling its partner to start a chemical chain reaction that travels down a neuron. Some animals have just the basic photoreceptors on their skins, such as some jellyfish, deep-sea snakes, and other marine creatures. A slightly more sophisticated version exists on the Japanese yellow swallowtail butterfly, which has these photoreceptors on its genitals, where they are helpful in completing coitus and laying eggs. Then, up a step on the evolutionary ladder, photoreceptor cells combine, and the animal can discern blurry shapes. Scallops have dozens or sometimes 200 eyes around the edges of their shells, which they use to detect food and avoid danger. (Mussels and oysters have none.) Finally the cells add lenses, and sharp vision begins in an inconceivably complex diversity of forms. But many primitive eyes remain, such as those on the arms of a starfish, just good enough to detect big objects. Humans, contrary to myth, have sharper vision than almost any other animal. This became an issue in the study of zebras. Was their striping camouflage to hide from lions or hyenas? Turns out lions’ and hyenas’ eyes are so dull they couldn’t possibly make out a zebra’s stripes until they were close enough to hear and smell it. Until then it looks just grey to them. Most animals’ visual acuity is at a level that humans consider legally blind. They rely more on other senses. Only eagles and other birds of prey have substantially sharper vision than humans. But that’s only an advantage in daylight. At night, many animal eyes, while not so sharp, are far more sensitive and thus more useful for nocturnal hunting. Not only the structure of an eye, but its position matters. Vultures, eagles and similar raptors with superb detail vision nevertheless regularly crash into wind turbine blades. They have a blind spot in their visual field directly ahead of them. Mallard ducks, by contrast, can see 360 degrees with no blind spots ahead, behind, or above. Seals have sharp vision upwards, poor vision looking down. When a seal swims upside down it’s scanning the water below with its best sight. Cows don’t see up or down very well but have a panoramic view of the horizon. Human eyes can distinguish flashes of light at around 60 cycles per second (Hz). Killer flies, that look like ordinary houseflies but eat them, see distinct flashes at more than 350 Hz. A human movie would look like a slow slideshow to them. There is no way a human hand can swat one. Some flycatcher birds, and many bees, dragonflies, and flies also have faster eyes than humans. The sweat bee Megalopta genalis can navigate in total darkness as well as other insects can in daylight. In ocean depths below 500 feet it’s dark all the time. This is the realm of the giant squid, the owner of the biggest and most sensitive eye, the size of a soccer ball, more than twice the size of a blue whale’s eye. The squid needs an eye that big to see sperm whales, their nemeses.
That’s only the beginning of the topic of vision. Next is the chapter on color. Tune in tomorrow to read my notes on this and the following chapters of An Immense World by Ed Yong.
Burrowing Owl Update
The Burrowing Owl this morning had left cloistered Perch A and returned to Perch B, where park visitors could see it from the paved trail outside the “art” fence. When I filmed it, the bird remained immobile, swiveling its head from side to side in a relaxed manner, very occasionally raising up slightly and opening its eyes wide in a brief alert, mostly with eyes half dimmed, semi-snoozing but always awake and responsive to its setting.
There was other good news as well. Thanks to an emergency intervention from Phil Rowntree, whose fine pictures have appeared here many times, a fresh set of “Area Closed: Burrowing Owl Sanctuary” signs went up on the fence in mid-afternoon. If you have any information about who ripped down the six existing signs late Tuesday or very early Wednesday morning, please contact firstname.lastname@example.org.
Setting aside reserved space for birds, even charismatic creatures like Burrowing Owls, has long aroused the wrath of dog libertarians, who see any limit on their pets’ freedom to roam and kill as violation of a God-given right. This was a hot issue when the Albany Plateau Burrowing Owl Mitigation Area fence was established. Many dog boundary signs have been vandalized in our park here over the years. Whoever ripped down the owl signs here this week was probably doing a symbolic substitute for tearing down the fence entirely. Although the “art” fence here is not a meaningful physical barrier to invading dogs or people, it’s better than no fence at all. Weak as it is, it marks a symbolic boundary where birds are owed respect and canines must keep out. For some dog owners that’s not acceptable. Most dog owners, it bears repeating, act responsibly. They know and obey park rules. Many love nature and appreciate birds. But there is an extremist minority among them that causes much harm.
Here is the Burrowing Owl in Perch B this morning: