1. How Do Animals Perceive the
World?
• Jakob von Uexküll’s Tick
• "...this eyeless animal finds the way to her
watchpoint [e.g. at the top of a tall grass
blade] with the help of only its skin’s
general sensitivity to light. The approach of
her prey becomes apparent to this blind and
deaf bandit only through her sense of smell.

2. Jakob von
Uexkull
The odor of butyric
acid, which
emanates from the
sebaceous follicles
of all mammals,
works on the tick as
a signal that causes
her to abandon her
post (on top of the
blade of grass/bush)
and fall blindly
downward toward
her prey.

3. A Tick’s World (Cont’d)
• If she is fortunate enough to fall on something
warm (which she perceives by means of an organ
sensible to a precise temperature) then she has
attained her prey, the warm-blooded animal, and
thereafter needs only the help of her sense of
touch to find the least hairy spot possible and
embed herself up to her head in the cutaneous
tissue of her prey.
• She can now slowly suck up a stream of warm
blood.

4. A Tick’s Three Sensory Cues
• Von Uexkull shows that the world of a
female tick is reduced to three sensory cues:
the smell of butyric acid, the warmth of a
mammal's skin, and the feel of a warm
liquid.
• At sexual maturity the tick mates with a
male, climbs to the tip of a branch, and
waits.

5. A Tick’s “Umwelt”
• No stimulus other than the smell of butyric acid
is detected. No light, no sound, no vibration, no
taste, no other smell.
• Amazingly, the female tick may sit dormant for as
long as 18 years sensing nothing and doing
nothing until molecules of butyric acid reach her
olfactory sense. When butyric acid is detected, the
tick drops off the branch. If it senses warmth, the
tick begins to burrow. If it senses a warm liquid, it
drinks, falls to the ground, lays its eggs, and dies.

6. A Tick’s “Umwelt” (Cont’d)
• Jakob von Uexkull (1934) who argued that to truly
understand animal behavior one must appreciate the
animal's "umwelt" or self-world. This self-world is
determined by the animal's sensory systems, the
means by which sensory information is processed and
perceived, and its action systems.
• To illustrate this approach, von Uexkull asks his
readers to "blow, in fancy, a soap bubble around
each creature to represent its own world, filled with
the perceptions which it alone knows."

8. The Sense Organs:
Windows to the World
• Sensory receptors are dendrites (one of three parts
of nerve cells) specialized to detect certain types
of stimuli.
• The five best known: taste, smell, hearing, vision,
and touch.
• Others involve: balance (rotational motion and
gravity), temperature, pain, electricity in some
fish, polarized light in birds, ultraviolet light in
some birds and insects, the earth’s magnetic field
in birds and sea turtles, and infrared in snakes.

9. The Sense Organs (Cont’d)
• Each type of sensory receptors detects a particular kind of
stimulus. When stimulation occurs, sensory receptors
initiate nerve impulses that are transmitted to the spinal
cord and/or brain. Sensation occurs when nerve impulses
reach the cerebral cortex. Perception is an interpretation of
the meaning of sensations.
• Sense of Hearing in humans: The ear has two sensory
functions: hearing and balance (equilibrium). The sensory
receptors for both of these are located in the inner ear, and
each consists of specialized hair cells that are sensitive to
mechanical stimulation (mechanoreceptors).

10. Sense Organs (Cont’d)
• Sense of Taste and Smell in humans: taste and smell are
due to chemoreceptors that are stimulated by molecules in
the environment. After molecules bind to receptor proteins
of taste cells and olfactory cells, nerve impulses go to the
cerebral cortex which determines taste and odor according
to the pattern of stimulation.
---since humans can respond to a range of sweet, sour,
salty and bitter tastes, the brain appears to survey the
overall pattern of incoming sensory impulses and takes a
“weighted average” of their taste messages as the
perceived taste.

11. Sense Organs (Cont’d)
• Sense of Touch in humans: The skin has receptors
that are sensitive to touch, pressure, pain and
temperature (these are mechanoreceptors,
chemoreceptors and thermoreceptors).
• Sense of Vision in humans: Vision depends on the
eye, the optic nerves, and the visual areas of the
cerebral cortex. The eyes’ rod cells are sensitive to
dim light and the cone cells are sensitive to both
bright light and colors (they are both
photoreceptors).

12. Senses in Animals
(Niko Tinbergen’s Comments, 1965)
• “…All [animals] may be said to live in different worlds,
since each perceives best only that part of the environment
essential to its success. Thus, how an animal behaves has
much to do with what its sense organs are and whether
these are few or man, simple or complex.”
• “What sort or stimuli do animals receive? …they are not
necessarily the same as those to which a human might
react. …animals, including man, have different ‘windows
to the world.’ Some have sensory equipment that in some
respects is much poorer than ours; in others, the senses are
far superior. There are even animals that react to stimuli
which we cannot detect at all—sights or sounds or smells
which we could not discover without artificial extensions
to our own sense organs”

15. Extraordinary Senses in Animals
• Bat & The Moth

24. Bees and Ultraviolet Light

27. Human Vision vs. Snake Infrared
“Vision”
• The human visual system is sensitive to a
portion of the electromagnetic spectrum (in
wavelength, the typical way of talking
about light waves, from a bit less than 400
nanometers to a bit more than 700 nm).
• Note that although human beings cannot see
ultraviolet rays or infrared rays, other
creatures are sensitive to those portions of
the electromagnetic spectrum.

28. Pit Vipers
• For example, pit vipers (e.g., rattlesnakes,
copperheads, water mocassins) have a pit organ near
each eye.
• These organs allow the snakes to detect infrared
radiation with greater precision than one might
expect.
• For example, when blinded (humanely, for example,
using electrical tape), these snakes will strike at a rat
in back of its head—thereby avoiding its sharp
teeth. Thus, the infrared world "seen" by these
snakes must be fairly detailed.

32. Electric Fish

33. Electroreception
• Electroreception, which is the detection of weak electric
fields, is widespread among vertebrates, with cases in all
classes of fishes, two orders of amphibians and even
mammals (the duck-billed platypus). This 'exotic' sense
seems to be an ancestral vertebrate trait, as it is present in
lampreys and cartilaginous fishes.
• Its spotty presence in particular vertebrate groups indicates
that electroreception has evolved (been 'reinvented') a
number of times during vertebrate evolution. Particularly
compelling evidence for the independent evolution of this
sense is its presence in certain species of African and
South American fishes.

34. Electroreception (Cont’d)
• Electroreception is also found the duck-billed platypus, a
primitive, egg-laying, monotreme mammal.
• In all cases, electroreception does not seem to be the
ancestral condition. Most modern boney fish species are
not electroreceptive. Similarly, electroreception in the
duck-billed platypus is probably a derived trait because it
is not characteristic of reptilians (from which mammals
evolved).
• Electrogenic fish produce electric signals by discharging
their electric organs, which consist of columns of modified
muscle cells (electrocytes).

35. Electroreception (Cont’d)
• Some electric organs generate strong discharges (hundreds
of volts) that are useful for stunning prey (the electric eel),
whereas others produce weak discharges (millivolts) that
are used for social communication and electrolocation.
• Species that have electric organs of the weak discharge
type produce either intermittent (pulse species) or periodic
(wave species) discharges. Both types of weakly-electric
fish also have electroreceptors that are tuned to the
species-specific higher frequencies found in their
discharges.

36. Electric Eel Uses EODs to Stun
Prey for Capture and Eating

37. Electric “Eels”
• Despite their serpentine appearance, electric
eels are not actually eels. Their scientific
classification is closer to carp and catfish.
• These famous freshwater predators get their
name from the enormous electrical charge
they can generate to stun prey and dissuade
predators. Their bodies contain electric
organs with about 6,000 specialized cells
called electrocytes that store power like tiny
batteries.

38. Electric Eels (Cont’d)
• When threatened or attacking prey, these cells will
discharge simultaneously, emitting a burst of at
least 600 volts, five times the power of a standard
U.S. wall socket.
• They live in the murky streams and ponds of the
Amazon and Orinoco basins of South America,
feeding mainly on fish, but also amphibians and
even birds and small mammals.
• They have poor eyesight, but can emit a low-level
charge, less than 10 volts, which they use like
radar to navigate and locate prey.

40. Electric Organ Discharge (EOD)
in Fish
• Electric fish can use electricity as a communicative device,
much as humans use auditory signals. Using its electric
organ, the fish produces an electric organ discharge
(EOD), which is broadcast through the surrounding water
and received by other fish in the environment.
• Detecting these signals other fish process various aspects
of the signal to determine its significance. Fish constantly
emit EOD's, which can express a fish's species, gender,
reproductive intent, social status, and even level of
aggression.
• Decoding electrocomminicative "fish speak" is a difficult
process, and much remains to be discovered. Each species
of electric fish varies its EOD differently to communicate
different cues.

41. Electric Fish

42. Electric Fish Communication

43. Electric Eel Relationships

44. Echolocation in Whales
and Porpoises
• Toothed whatles (dolphins, porpoises, river dolphins, orcas
and sperm whales) use echolocation (or biosonar) in their
underwater habitat becaise it has favourable acoustic
characteristics and vision is extremely limited.
• Toothed whales emit a focused beam of high-frequency
clicks in the direction that their head is pointing. These
sounds are reflected by the dense concave bone of the
cranium and an air sac at its base. Most toothed whales use
clicks in a series, or click train, for echolocation, while the
sperm whale may produce clicks individually. Different
rates of click production in a click train give rise to the
familiar barks, squeals and growls of the bottlenose
dolphin.

45. Echolocation in Whales
and Porpoises
• Echoes are received using the lower jaw as the primary
reception path, from where they are transmitted to the
inner ear via a continuous fat body. Lateral sound may be
received though fatty lobes surrounding the ears with a
similar acoustic density to bone.
• Some researchers believe that when they approach the
object of interest, they protect themselves against the
louder echo by quieting the emitted sound. In bats this is
known to happen, but here the hearing sensitivity is also
reduced close to a target.

46. Echolocation Apparatus in a
Bottlenosed Dolphin

48. Sensing the Earth’s Magnetic Field
• Both migratory birds and sea turtles are able to sense the
earth’s magnetic field and appear to be able to use it in
navigation.
• An experiment with a migrating Australian bird, the
silvereye, provides evidence.
--1. Scientists subjected migrating silvereyes to a strong
magnetic pulse; the result was that the orientation of their
subjects different significantly to that of untreated control
birds; it took ten days for most of the treated birds to
correct their direction.
--2. Conclusion: adult silvereyes rely upon magnetic field
information during their migratory journeys.
Graphic: G. Scott Fig. 4.18, p. 89.

49. Atlantic Salmon Annual Migration
Route

50. Sensing the Earth’s Magnetic Field
• Another conclusive experiment involved green sea
turtles that migrate over long distances.
• Fig. 4.46, p. 139, Alcock: experimental
manipulation of the magnetic field affects the
orientation of green sea turtles.
• Turtles that experience the magnetic field
associated with an area to the north of their actual
location swim south; turtles that sense the
magnetic field of an area to the south of their
actual location swim north.

51. Green Turtle Annual Migration
(to/from Ascension Is. to the Coast of Brazil)

52. Sensing Ultraviolet
and Polarized Light
• Hypotheses: monarch butterfly navigation is dependent on
ultraviolet radiation as well as polarized sunlight (p.
136-137, Alcock).
• A monarch flight cage was covered with a UV interference
filter, which screened out this component of sunlight
(which humans can’t see).
• The monarchs became confused and many stopped flying
altogether; most individuals resumed flight, however, as
soon as the filter was removed.
• A similar experiment with polarized light with monarchs
yielded similar results: monarchs can orient to polarized
light, using it to consistently orient to the southwest—the
direction of their annual migration