Introduction

• Umwelt = part of the world that an animal can experience and perceive
  • Each is limited, but feels all-encompassing… an illusion
• Book about diversity, not superiority
  • About animals for animals, not for human uses
• Senses come at an energetic cost → no animal can sense everything well
• Hard to categorize senses cleanly — eg. platypuses sense electric fields & pressure with same organ, is this one or two distinct senses?
• Humans are very biased by vision when thinking about other senses/other umwelts (our language is full of visual metaphors)
  • Alexandra Horowitz → must take "imaginative leap" when thinking about other animals' senses
  • Studying/training in the arts, other divergent cognitive differences (eg. color blindness, face blindness) can also help

1: Leaking Sacks of Chemicals

• Dogs, when inhaling, have separate airstream that goes to olfactory epithelium → uninterrupted smell input, unlike humans (pause at each exhale); shape of nostrils further aids
• Very few smell words in English (stinky, fragrant, musty), but other languages have many more
• Pheromones = standardized chemical messengers between same species, mean the same thing
• Main purpose of olfaction → navigation?
• DMS = odorant released by bountiful seas, detected by seabirds (give ocean an olfactory topology)
• Vomeronasal organ = secondary scent organ in some animals (dogs, elephants, snakes, horses, cats…) → has its own receptors and nerves
  • Main scent organ for snakes (also unique because smell with tongue, forked → stereo info)
• Difference between smell and taste?
  • Taste is reflexive & innate, smell is not— reactions to scent must be learned via experience
  • Taste is much simpler: fewer receptors (only 5 in humans), used to make binary decisions rather than complex ones like navigation (eg. "Should I eat this?")
• Gustatory umwelts shrank and expanded to match needs of different species… ex. pandas and koalas have more bitter receptors and no sweet receptors since they only eat leaves

2: Endless Ways of Seeing

• Vision = based on similar GPCRs to olfaction, but sense light (smelling light?)
  • Opsins bound to chromophore which detects photons, conformational change signals to opsin
• Eyes come in very diverse forms → widely varying visual umwelts
• Don't have to see images to sense visual stimuli
• Different visual acuities (cycles per second, "sharpness" of sight— humans are great at this), speed of processing (in Hz)
• Many strategies for night vision: slower "shutter speed," larger eyes, reflective layer to bounce back missed photons
  • Why do giant squid have such massive, soccer-ball sized eyes despite diminishing returns of larger eye size in the deep sea? Only animal that benefits from what huge eyes can do, spotting large glowing things far away (like sperm whales that bounce up against bioluminescent shrimp)

3: (A Chapter on Color)

• Color vision stems from three types of cones that are stimulated differently by blue, green, and red light
• Also depends on neural network that compares the stimulation levels— opponency → raw signal from three cones can create entire spectrum of rainbow (in humans)
  • Unlike some animals, where specific cones trigger specific responses (water fleas)
  • Opponency offers constancy of color vision
• Most mammals (dogs, horses) are dichromats, so why are humans and most primates trichromatic? Perhaps to find fruit and such in the forest?
• Most animals that see color can see UV— we are the exception!
  • Reindeer can se non-UV reflecting moss/lichen vs background of UV reflecting snow
  • Tetrachromats see an entire new dimension of color, different conception of white
• Some animals have more than four kinds of photoreceptors, but additional ones almost certainly just hardwired for specific tasks
• In general: signal evolves in response to the eye of the beholder

4: The Unwanted Sense (Pain)

• Sensed by nociceptors
• Nociception = sensory process that detects damage, vs pain, the much more subjective concept of the suffering it causes (sensory vs emotional processes)
• Big ethical/moral question as to what animals can feel pain— not as simple as how large or complex their brains are

5: So Cool (Heat)

• TRP channels = most well studied temperature sensors
• Thermotaxis = ability of animals to follow and sense changes in temperature
• How do you sense heat from afar?
  • As temp increases and molecules move faster, emit electromagnetic radiation, primarily in IR spectrum (what you feel near a fire)
  • Certain beetles can sense radiant heat via IR light by weird "pits" of tiny liquid filled spheres that expand when absorb radiation, triggering signal → can sense fires from dozens of miles away
  • Similar to mosquitos, pit vipers
• Dogs keep their noses cooler than room temp like above animals → can they sense heat from afar? Seems like it

6: A Rough Sense (Contact & Flow)

• Different mechanoreceptors respond to different kinds of touch— steady, vibration, slip, etc. (different "flavors")
• Star-nosed mole's sense of touch via its… star nose… is incredibly fast and acute
• Most birds have mechanoteceptors on their bills/beaks
  • Ducks can filter food from muck in lakes by touch
  • Seabirds foraging for food buried in the sand can "touch at a distance" by sensing pressure waves of water in the sand being distorted by hard objects below
• Body whiskers on manatees → sense flow of water, can detect tiny motions around them (helpful for sensing currents, other manatees)
• Whiskers of seals can sense hydrodynamic wake of swimming fish precisely from large distances → can sense what was, not just what is
  • Have uniquely designed whiskers that limit interference with what they are sensing
• Fish have had millions of years more to evolve flow-sensing with their
• Birds and bats do the same via feathers to sense and respond to air currents

7: The Rippling Ground (Surface Vibration)

• Could argue that previous chapter's "flow," these surface vibrations, and sound are all aspects of hearing, but still have differences in how/which animals use them
• Insects (leaf hoppers and tree hoppers), elephants, spiders all detect/use this sense a lot
• Spider's web is a part of itself; spinning different webs changes it's umwelt (which vibrations it can sense, eg. what size of prey)

8: All Ears (Sound)

• Asymmetric ears on an owl give it more precision in determining vertical position of a source of sound
• Lessons from diversity of insect ears
  • Hearing is helpful but not necessary (ears evolved many times in different ways, but most insects don't have them)
  • Hearing can be incredibly simple — automatic recognition, reflexive reaction
  • Animal hearing can drive evolution of animal calls and vv
• Some species of birds have much more fine grained, FAST hearing than humans and other birds
• Can distinguish between two adjacent tones better when integrating a sound over longer time, but at the cost of missing rapid changes in note
  • Birds can change what type of listening they do depending on season (eg. mating calls that need to have faster pitch or speed) → happens by changes in hormones
• Large whales (blue whales, fin whales) produce such loud and deep (infrasound) noises that they can travel thousands of miles, theoretically across an entire ocean
  • Allow whales to build of geographical maps of the ocean?
  • Elephants too communicate in infrasound
• Many rodents, etc. produce ultrasonic calls
  • Helpful for smaller creatures to use sound to locate sources because small wavelength
  • Smaller range → don't attract predators (also makes it hard to study and detect)

9: A Silent World Shouts Back (Echos)

• Bats and toothed whales are only two masters of echolocation
• Different than other senses because involves putting energy into the system
• Bats have to "scream" very loudly, so have to contract middle ear when calling to prevent deafening themselves, then open ear back up to detect echo
  • Often make "silly mistakes," because echolocation is extremely mentally taxing, esp at speed → also rely on memory, heuristics
  • Most bats = FM (frequency modulating), but some are CF (constant frequency) → can detect own echos with more sensitivity
• Even people who are blind can echolocate via clicking

10: Living Batteries (Electric fields)

• Another "active" sense
• Many fish can generate electric fields— eg. certain catfish can generate 90 V!
  • Evolved ability by modifying other electrically active cell types like muscle cells, neurons → electrocytes, align cells to build up large voltages
  • Detect signal with electro receptors
• Electric eels and torpedo rays are most strongly electric
  • Other elephant and knife fish are more weakly electric → use electric fields to sense surroundings and communicate (the core of their unwelt) → active electrolocation
• Electrolocation based on insulating/conductive properties of items and surroundings → very sensitive to metal, salinity, capacitance (usually sign of living things)
• Big difference from other senses → signal of electric fields does not travel, so the sense is instantaneous (and omnidirectional)
• Evolved from lateral line and analogous to how gosh sense their surroundings from water currents
• Used to communicate with other fish, even as part of mating preferences, etc.
  • Can only send signals short range otherwise requires large, energetically expensive voltages, but can listen passively via electroreceptors
  • Communication and navigation require same electric pulses, so literally must stop awareness of surroundings to communicate
• Sharks → passive electroreception, can detect natural electric fields of living organisms in water
• Some mammals too have passive electroreception— certain dolphin species, platypus, echidna
• Ancient sense! But lost in most vertebrates, to be gained in aforementioned species
• For a long time, assumed electroreception could only work in water, because air is incredibly strong insulator… but then, bees!
  • Atmosphere itself contains vertical voltage gradient, about 100 V per meter
  • Flowers, grounded in earth, have negative charge; bees flying through the air build up positive charge perhaps by electrons knocked off by debris → even before a bee lands on a flower, pollen grains jump to the insect
  • Bees can detect electric fields from flowers (distinct at edges especially)
  • Tiny hairs covering bees that deflect and signal changes in air current are also moved by electric fields; extended sense of touch
• Spiders too sense electric fields, can also "ride" them

11: They Know the Way (Magnetic fields)

• Sense we know least about, despite knowing it's been there for a long time— hypothesis in need of evidence
• Earth's geomagnetic field guides migrations… how do animals like birds sense such an incredibly weak signal? Could prove they did in experiments
• How to test whether animals like whales have a magnetic sense? Correlated whale movement with solar storms, which mess with magnetic fields → solar storms correlated with higher chances of whales beaching themselves
• Sea turtles → two magnetic senses… magnetic compass and inclination/intensity "map"
• Many species create magnetic imprint of birthplace to return to
• How to find magnetoreceptors? Don't need to be exposed since magnetic fields pass easily through flesh

12: Every Window at Once (Uniting the senses)

• Often require multiple senses/signals to lead to an outcome (eg. mosquitos tend toward heat but only if in the presence of CO2)
• All sense organs must distinguish between exafference (signals coming from outside) and reafference (signals coming from within, eg. turning your head)
  • Motor commands are duplicated and sent to sensory system, which simulates the self-produced signal
• Sentience = process of sorting perceptual experiences into self-generated and other-generated
• Octopus: each tentacle has an umwelt dominated by taste and touch, while the main body's is dominated by vision— though probably crosstalk between the two

13: Save the Quiet, Preserve the Dark (Threatened sensescapes)

• Light pollution ever increasing year on year in size and intensity
• Tribute in lights from 9/11 interferes with huge migration of birds, waylaying over a million
• Sound pollution → some birds sing louder, at different pitches to be heard
• Most damaging effect of sound pollution is loss of the "background" noise, eg. rustling of leaves an owl listens to for pray, flap of wings that warns the mouse
• Growing shipping fleets adding tons of noise pollution to the oceans, making many species vulnerable
• Light and sound pollution are an "ecological gimme"— can be stopped as soon as lights are turned off, engines are quieted
• Many solutions exist (turning lights red, not shining them over the horizon, slowing boats, sound barriers), but societal/economic pressure does not
• Idea of "the wild" separates us from the nature that we live within

Interesting article about how AI could be used to reconstruct an animal’s umwelt…