Transcript magnetic field

大學部 生態學與保育生物學學程 (必選)
2010 年 秋冬
導航機制(Mechanisms of Orientation and
Navigation
─動物行為學 (Ethology)
鄭先祐(Ayo)
國立 臺南大學 環境與生態學院
生態科學與技術學系 教授
Ayo NUTN Web: http://myweb.nutn.edu.tw/~hycheng/
Part 2. 存活 (與環境的互動關係)
 生物時鐘 (Biological Clocks)
 導航機制 (Mechanisms of Orientation and Navigation)
 空間分佈的生態學與演化學 (The Ecology and
Evolution of Spatial Distribution)
 覓食行為 (Foraging Behavior)
 抗掠食行為 (Antipredator Behavior)
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09 導航機制 (Mechanisms of Orientation
and Navigation)
 Levels of Navigational ability
 Multiplicity of orientation cues
 Visual cues
 Magnetic cues
 Chemical cues
 Electrical cues and electrolocation
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Animals depend on oriented movements
 Both within and between habitats
 Animals respond to a complex and changing
environment by positioning themselves correctly in it

And by moving from one part of it to another
 Animals depend on proper orientation to key aspects of
the environment

For migration, seeking a suitable habitat, looking for
food returning home, searching for a mate, or
identifying offspring
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Levels of navigational ability
 Many animals travel between home and a goal
 But they do not all do this in the same manner
 Animal strategies for finding their way fall into three
levels
1. Piloting (引導)
2. Compass orientation (羅盤定位)
3. True navigation (真領航)
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1. Piloting
 The ability to find a goal by referring to familiar
landmarks

The animal may search randomly or systematically for
landmarks
 The guidepost may be any sensory modality
 Magnetic cues guide sea turtles during their oceanic
travels
 Olfactory cues guide salmon during their upstream
migration
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2. Compass orientation
 Animals head in a
geographical direction
without using landmarks

Use the sun, stars, and
earth’s magnetic field as
compasses
 If they are displaced before
beginning migration

Animals can end up in
ecologically unsatisfactory
places
Compass orientation is indicated
if an animal is moved to a
distant location and does not
compensate for the relocation
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Compass orientation
Displaced birds did
not reach their normal
destination and ended
up in ecologically
unsatisfactory places
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Uses for compass orientation: vector
navigation
 Compass orientation can be used in
 Short-distance and long-distance navigation
 Vector navigation: an inherited (innate) program
that tells juveniles in which direction to fly and how
long to fly


Birds in the laboratory flutter in the direction in which
they would be flying if they were free
Captive birds cease their activity at the same time as
free-living birds have completed their migratory
journey
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Animals can change compass bearing
 Many species (i.e. that fly from central Europe to Africa)
change compass bearing during their flight
 Garden warblers and blackcaps in the laboratory
change the direction in which they flutter in their cages

At the same time free-flying members change direction
 Migratory direction is inherited
 Offspring of crossbreeding two populations of blackcaps
that had different migratory directions oriented in a
direction intermediate between their parents
 Migratory direction is inherited by additive effects of genes
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 ←The Blackcap, Sylvia atricapilla,
is a common and widespread
sylviid warbler which breeds
throughout northern and temperate
Europe. the Blackcap's closest
living relative is the Garden
Warbler which looks different but
has very similar vocalizations.
 →The Garden Warbler, Sylvia
borin, is a common and
widespread typical warbler which
breeds throughout northern and
temperate Europe into western
Asia. This small passerine bird is
strongly migratory, and winters in
central and southern Africa.
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Uses for compass orientation: path
integration
 Path integration (dead reckoning): the animal
integrates information on the sequence of direction and
distance traveled during each leg of the outward journey

Then, knowing its location relative to home, the animal
can head directly there, using its compass(es)
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Path integration
 Information from the outward journey is used to
calculate the homeward direction (vector)

Path integration may be a type of vector navigation
 Estimates of distance and direction are adjusted
 For displacement due to current or wind
 Close to home, landmarks pinpoint the exact location
of home
Desert ant
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Many animals use path integration
 While foraging, a desert ant wanders far from its nest
 After locating prey, the ant heads directly toward home
 The ant knows its position relative to its nest
 Each turn and the distance traveled on its outward trip
 To determine the direction and distance of its outward
route


Direction is determined using the pattern of polarization of
skylight, which is caused by the sun’s position
Distance integrates the number of strides and stride length
(a “pedometer”)
 At home, cues in the nest reset the path integrator to zero
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 It is set again by the next
outward journey
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3. True navigation
 The ability to maintain or establish reference to a goal,
regardless of its location, without use of landmarks
 The animal cannot directly sense its goal

If displaced while en route, it changes direction to head
again toward its goal
 Only a few species (i.e. homing pigeons) have true
navigational ability


Oceanic seabirds and swallows (燕子)
Sea turtles and the spiny lobster
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 An animal that finds its way by using true navigation
can compensate for experimental relocation and travel
toward the goal.
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Astounding feats(令人驚奇的事蹟) of
migration
 Different species use different navigational mechanisms
 An arctic tern circumnavigates the globe
 A monarch butterfly flutters thousands of miles to Mexico
 A salmon returns to the stream in which it hatched
 Orientation systems include: multiple cues, a hierarchy
of systems, transfer of information among various
systems
 A species can use several navigational mechanisms


If one mechanism becomes inoperative, a backup is used
Navigational systems may use multiple sensory systems
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Visual cues: landmarks
 An easily recognizable cue along a route that can be quickly
stored in memory to guide a later journey

Based on any sensory modality, but is most commonly visual
 The digger wasp relies on landmarks to relocate its nest
after a foraging flight



A ring of 20 pine cones was placed around the nest’s opening
When a female wasp left the nest, she flew around the area,
noting local landmarks, and then flew off in search of prey
When the ring of pinecones was moved, the returning wasp
searched the middle of the pine cone ring for the nest opening
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Orienting with landmarks
 Homing pigeons wearing frosted contact lenses did not
see well

Their flight paths were still oriented toward home
 Pigeons do not need landmarks to guide their journey
home

But they may use landmarks when they are available
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Models of landmark use
 Species use landmarks in different ways
 One model of landmark use: the animal stores the image
of a group of landmarks in its memory, almost like a
photograph


Then it moves around until its view of nearby objects
matches the remembered “snapshot
A series of memory snapshots might be filed in the order
in which they are encountered
 Desert ants use path integration to return to the nest
 They also use landmarks, especially when they have
almost reached the nest
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Desert ants use memory snapshots of landmarks
 Close to the nest entrance, they search systematically to
find the nest’s opening

The search strategy varies with the species and number of
landmarks
 If available, ants use landmarks
 If the direct path is unfamiliar
 At a clearing, it uses path integration
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Visual cues: sun compass
 Many animals use the sun as a celestial compass
 Determining compass direction from the position of the
sun
 The specific course that the sun takes varies with the
latitude of the observer and the season of the year

But it is predictable
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 The sun follows of predictable path through the sky that
varies with latitude and season.
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The sun can be used as a compass
 If the sun’s path and the time of day are known
 The sun appears to move at about 15° an hour
 Species that take short trips do not adjust their course
 An animal traveling for long periods compensates for the
sun’s movement



It measures the passage of time and adjusts its angle with
the position of the sun
After 6 hours of travel, an animal switches from having the
sun 45° to its left to a 45° angle, with the sun on its right
Time is measured by using a biological clock
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Daytime migrants navigate by the sun
 Orientation (directionality) of
migratory restlessness is lost when the
sun is blocked from view
 Caged starlings are daytime migrants


They lose their directional ability
under an overcast sky
When the sun reappears, they orient
correctly again
 Birds orient to a new direction of the
“sun” when a mirror is used to change
the apparent position of the sun
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Starling (歐掠鳥)
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Experiments using migratory restlessness
 An orientation cage has 12 food
boxes encircling a birdcage



Birds were trained to expect food
in a box in a certain compass
direction
As long as the birds could see the
sun, they approached the proper
food box
They compensate for the sun’s
movement
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Compensation for the sun’s movement
 Is through the biological clock
 Which can be reset by artificially altering the light-dark
regime
 Exposing a bird to a light-dark cycle that is shifted so that
the lights come on at noon instead of 6 am


Sets animal’s body time six hours later than real time
Orientation is shifted 90° (6 x 15°) clockwise, west instead
of south
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 A clock-shift experiment demonstrates time-
compensated sun compass orientation.
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Visual cues: star compass
 Many species of bird migrants travel at night
 Steering their course using stars
 Caged warblers housed in a planetarium oriented
themselves in the proper migratory direction for that
time of year


When the star pattern of the sky was rotated, the birds
oriented according to the sky’s new direction
When the dome was diffusely lit (光線擴散), the birds
were disoriented
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Star compass orientation in indigo
buntings
 In planetarium(天象儀) studies, these birds rely on the
region of the sky within 35° of Polaris (北極星)
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Indigo Bunting
 The Indigo Bunting,
Passerina cyanea, is a
small seed-eating bird in
the family Cardinalidae.
 It is migratory, ranging from southern Canada to
northern Florida during the breeding season, and from
southern Florida to northern South America during the
winter.
 It often migrates by night, using the stars to navigate.
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Stars rotate around Polaris (北極星)
 Polaris provides the most stationary reference point in
the northern sky

Other constellations rotate around it
 Birds learn that the center of rotation of the stars is in
the north

Which guides their migration northward or southward
 It is not necessary for all constellations to be visible at
once
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 The stars rotate around Polaris, the North Star. The positions
of stars in the northern sky during the spring are shown here.
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The axis of rotation gives directional
meaning
 Once their star compass has been set, birds do not
need to see the constellations rotate

Simply viewing certain constellations is enough
 The star compass has been studied in only a few
species

Garden warblers and pied flycatchers also learn that
the center of celestial rotation indicates north
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Young birds were oriented to
Betelgeuse(參宿四，位於獵戶座)
 Birds that had experienced Betelgeuse, not Polaris, as the
center of rotation interpreted the position of that star as
north

And headed away from it for their southern migration
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 The orientation of indigo buntings to a stationary
planetarium sky after exposure to different
celestial rotations.
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Visual cues: polarized light
 Many animals orient correctly even when their view of the
sky is blocked
 Another celestial orientation cue is available in patches of
blue sky
 Light consists of many electromagnetic waves vibrating
perpendicularly to the direction of propagation
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The nature of polarized light
 Unpolarized light: light waves vibrate in all possible
planes perpendicular to the direction in which the
wave is traveling
 In polarized light: all waves vibrate in only one plane
 Sunlight passing through the atmosphere becomes
polarized by air molecules and particles

The degree and direction depend on the position of the
sun
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 The sky viewed through a polarizing filter to show the
pattern of skylight polarization at (a) 9am (b) noon, and (c)
3pm. The diagrams below show the pattern of polarization.
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The pattern of polarized light
 Is related to the sun’s position
 One aspect of this pattern is the degree of polarization
 The light at the poles is unpolarized
 Becoming more strongly polarized away from the poles
 The e-vector: the direction of the plane of polarization
also varies according to the position of the sun


It is always perpendicular to the direction in which the
light beam is traveling
The pattern moves westward as the sun moves
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Uses of polarized light in orientation
 Polarized light reflected from shiny surfaces (i.e. water
or a moist substrate)

Attracts some aquatic insects to suitable habitat
 Horizontally polarized light reflected from the surface
of a pond helps the backswimmer locate a new body of
water
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Backswimmers
 Backswimmers get their
common name from their
characteristic habit of
swimming on their backs.
Although they must surface
for air, they often swim
around below the surface of
the water.
 Backswimmers or Back-swimmers (Family Notonectidae)
are common in ponds and other still waters here in
southeastern Arizona and throughout most of the rest of
North America.
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The plane of polarization is an orientation cue
 Polarized light is used as an axis for orientation
 Salamanders living near a shoreline use the plane of
polarization to direct their movements toward land or
water
 It can determine the sun’s position when blocked from
view

And provide orientation cues at dawn and dusk, when the
sun is below the horizon
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Magnetic cues
 Magnetic sense helps an organism locate a preferred
direction

i.e. when bacteria swim toward the muddy bottom
 The earth’s magnetic field may also orient nest building
 In the Ansell’s mole rat, or roosting place of bats
 A magnetic compass evolved in non-migratory birds first
 Optimized paths to and from nest, feeding, and drinking sites
 Advantages to using the earth’s magnetic field as a
compass:


Used where visual cues are limited or absent
Unlike celestial cues, it is constant year round, night and day
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Cues from the earth’s magnetic field
 The magnetic poles are shifted slightly from the
geographic, or rotational, poles
 The earth’s magnetic declination: the difference
between the magnetic pole and the geographic pole


Small in most places (< than 20°)
Magnetic north is usually a good indicator of
geographic north
 Polarity, inclination, and intensity of the earth’s
magnetic field vary with latitude to provide three
potential orientation cues
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 The earth’s
magnetic field.
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The magnetic field provides
orientation cues
 Spiny lobster and certain fish and birds, rats and
bats respond to polarity
 Most birds and sea turtles use the angle of
inclination



They distinguish between “poleward” (steep lines of
force) and “equatorward” (lines of force parallel to
the earth)
The horizontal component of the earth’s field (the
polarity) indicates the north-south axis
The vertical component (the inclination of the field)
tells whether it is going toward the pole or equator
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Ansell’s mole rats orient using polarity
 They build nests in the southeastern part of their
enclosure
 When the horizontal component (the polarity) was
reversed

The rats built nests in the northwest sector of the arena
 When the vertical component (the angle of inclination)
was inverted

They continued nesting in the southeast sector
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 The earth’s magnetic field can serve as a compass
(a) mole rats respond to the polarity (horizontal
component) of the ambient magnetic field.
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Birds orient using the inclination angle
 In the laboratory, European robins oriented in the
proper direction even without visual cues
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Birds orient using the inclination angle
 Birds use the inclination of the lines of force (vertical
component of the earth’s magnetic field) as a compass.
The lines of force are steepest at the poles and
horizontal at the equator.
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Homing pigeons use the angle of inclination
 On cloudy days, pigeons rely on magnetic cues instead
of their sun compass

Orienting as if north is the direction where the magnetic
lines of force dip into the earth
 Birds that were misdirected by
reversed magnetic information

Headed away from home
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The Earth’s magnetic field serve as a
magnetic compass
 Animals respond to the intensity of the
geomagnetic field




Bees
Homing pigeons
Sea turtles
American alligator
 If changes in magnetic intensity can be
sensed

The gradual increase in strength between
the equator and the poles could also serve
as a crude compass
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An inherited migratory program
 Migratory birds inherit a program telling them to travel in
a geographical direction based on magnetic cues for a
certain amount of time

They fly toward the equator (horizontal lines of force) in the
fall and toward the pole (vertical lines of force) in the spring
 Some birds cross the equator during migration and keep
going



They reverse their migratory direction with respect to the
inclination compass
They now fly “poleward” instead of “equatorward”
Experience: the switch that causes the birds to fly
“poleward”
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The sensitivity of the magnetic compass
 Corresponds to the strength of the earth’s magnetic
field
 A bird does not respond to magnetic fields that are
stronger or weaker than typical in the area where it
has been living
 Sensitivity may be adjusted by exposure to a field of a
new strength for a period of time

Responsiveness is fine-tuned during migration
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The magnetic compass of sea turtles
 Sea turtles travel tens of
thousands of kilometers during
their lifetimes


Continuously swimming for
weeks
With no land in sight
 Loggerhead sea turtles are
guided by the earth’s magnetic
field
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A hatchling sea turtle’s magnetic compass
 Is based on the inclination of
the magnetic lines of force

Similar to a bird’s compass
 Hatchlings swim toward magnetic northeast in the
normal geomagnetic field

And continue to do so when the field is experimentally
reversed
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A sea turtle’s journey begins after hatching
 Using local cues to head toward the ocean
 When they first enter the ocean, they swim into the
waves

To maintain an offshore heading, taking them out to sea
 In the open ocean, waves are not a navigational cue
 They can come from any direction
 Sea turtles maintain the same angle with the magnetic
field that they assumed while swimming into the waves
to stay on course
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Is there a magnetic map (磁場地圖)?
 True navigation requires not only a compass but also a
map


The map is used to know one’s position relative to the
goal
A compass guides the journey in a homeward direction
 An animal has a magnetic map if it can obtain
positional information from the Earth’s magnetic field

Relative to a target or goal
 The map may be inherited or learned
 Specific or general
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Magnetic signposts (磁場路標)
 Magnetic maps consist of inherited responses to
landmarks

Signposts (路標) trigger changes in direction
 Signposts occur along the migratory pathways of the
pied flycatcher



Key geographical locations have characteristic magnetic
fields
These fields act as signposts telling them to shift flight
direction
Birds avoid the Alps, Mediterranean Sea, and central
Sahara
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Magnetic signposts affect sea turtles
 Triggering changes in swimming direction during the
open-sea navigation of sea turtles
 Hatchling loggerhead sea turtles first swim toward
magnetic northeast using the earth’s magnetic field
as a compass



Bringing them to the Gulf Stream
Then to the North Atlantic gyre (北大西洋流), a
circular current that flows clockwise around the
Sargasso Sea (藻海)
Where they remain for 5 to 10 years
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Young sea turtles are programmed to swim
 Hatchling loggerheads that had never been in the
ocean swam in a direction that would keep them in the
gyre if they had been migrating
 Regional differences in the earth’s magnetic field
serve as navigational beacons (導航的燈塔)


Guiding the open-sea migration of young loggerheads
They have no conception of their geographic position or
goal
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 Magnetic
signposts in
the earth’s
magnetic field
may direct
juvenile sea
turtles in the
proper
direction to
remain within
the North
Atlantic gyre.
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The magnetic field is a map
 Animals use the earth’s magnetic field as a map to locate
their position relative to a goal

Using inclination and the intensity of the earth’s magnetic
field
 The geomagnetic field may be more than a compass
 Birds released at magnetic anomalies prefer magnetic valleys
 They detect and respond to spatial variability of the
geomagnetic field
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 The flight paths of pigeons in magnetic anomalies. The paths of
these pigeons seem to follow the magnetic valleys, where the field
strength is closer to the value at the home loft.
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Sea turtle migration
 As a sea turtle matures, it learns the geomagnetic
topography of specific areas

This is part of the map it uses to locate an isolated target
(i.e. a nesting beach)
 After spending years in the North Atlantic gyre
 Sea turtles migrate between summer feeding grounds and
winter feeding grounds in the south
 Adults return to nest on the same beaches where they
hatched
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Sea turtles migrate with extraordinary precision
 The earth’s magnetic field provides a global positioning
system that tells them their position relative to a goal
 Juveniles and adults use the geomagnetic field as
navigational map

A more complex use than hatchlings
 The magnetic field tells the turtle whether it is north or
south of its goal

It moves in the appropriate direction until it encounters
other cues that identify the feeding grounds
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 As sea turtles mature, they
use the earth’s magnetic
field to determine their
location relative to home.
Sea turtles return to the
same feeding grounds
every year.
 The turtle swam in a
direction that would return
them to their feeding
grounds (the test site) if
they actually had been
displaced.
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Light-dependent magnetoreception
 Animals sense the earth’s magnetic field through at
least two types of magnetoreceptors: light-dependent
and magnetite
 Light-dependent magnetoreception: involves
specialized photoreceptors

Is light dependent
 Certain animals may “see” the earth’s magnetic field
 Photoreceptor molecules absorb light better under
certain magnetic conditions
 The amount of light absorption provides information
about the local magnetic field
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 Seeing the earth’s magnetic field. The visual field of a
bird flying.
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Light dependent magnetoreception in birds
 The magnetoreceptor is located in the right eye
 Birds cannot remain oriented to a magnetic field in darkness
 Light must of specific wavelengths
 Blue light is needed to remain oriented to a magnetic field
 Birds may orient to red light if they are given time to adjust
 Cryptochrome: a photopigment involved in
magnetoreception


Stimulates photoreceptors differently depending on the
orientation of the magnetic field
Migratory birds sense the magnetic field as a visual pattern
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Cryptochromes
 Cryptochrome是一種藍光/
紫外光受體，與果蠅生物
鐘的控制有關。
 Cryptochrome可用作磁場
的一種傳感器。
 Cryptochromes are a class of blue light photoreceptors of plants
and animals. They form a family of flavoproteins that regulate
germination, elongation, photoperiodism, and other responses in
higher plants. Cryptochromes are involved in the circadian
rhythm of plants and animals, and in the sensing of magnetic
fields in a number of species.
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Cryptochrome
 Cryptochrome absorbs blue-green light
 Wavelengths important for magnetic orientation
 In night-migratory birds, cryptochromes are produced at
night
 Nonmigratory birds produce cryptochromes during the day
 Cryptochrome-containing cells of the retina connect to
neurons in a brain region called Cluster N


Neurons are active when night-flying migrants orient to a
magnetic field
The retina and cluster N are connected through the
thalamus, a brain region important for vision
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Magnetite (磁鐵礦)
 Magnetite: a magnetic mineral in animals
 It orients to the geomagnetic field
 Found in bees, trout, salmon, birds, and sea turtles
 In vertebrates, these deposits are found in the head or skull
 It can twist to align with the earth’s magnetic field,
stimulating a stretch receptor
 In the rainbow trout, nerves contain fibers that respond
to magnetic fields
 Along with their light-dependent inclination compass,
birds have magnetite deposits in their upper beak
 The polarity compass of bats is based on magnetite
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Two magnetoreceptor systems
 Animals might have one or both types of magnetic
sensitivity


Light-dependent and magnetite
Each serving a different purpose
 Eastern red-spotted newts
 Use a light-dependent magnetic compass based on the
inclination of the magnetic lines of force when orienting
toward the shore
 Their homing ability is sensitive to polarity changes
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Magnetoreception in migratory birds
 The two mechanisms of magnetoreception serve
different functions


The light-dependent mechanism: a magnetic compass
The magnetite based mechanism: detects minute
variations in earth’s magnetic field and is part of the
magnetic “map” receptor
 To use the geomagnetic field as a map, an animal
compares the local intensity of the field with that at
the goal
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Juvenile vs. adult silvereye receptor systems
 Adult, not juvenile, migrants have a navigational map
 Juvenile silvereyes remained oriented in the appropriate
migratory direction after a magnetic pulse



They have not yet formed a magnetic map
Their orientation is based on an innate migratory program
They use their magnetic compass, based on the lightdependent magnetoreception process, to head in the
appropriate direction
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Chemical cues
 Some species use olfactory cues for orientation during
homing
 Olfaction and salmon homing



Salmon hatch in the cold, clear fresh water of rivers or
lakes and then swim to sea
After several years, they reach their breeding condition
and return to the very river from which they came
Swimming upstream, they return to the specific location
of the natal stream in which they were born
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Salmon return to their incubation site
 Researchers buried salmon embryos at the bottom of a
pond


The embryos emerged and migrated to the sea
And then migrated back to the creek
 The marked salmon returned to the site of their
incubation

The pond
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 A map of Hansen creek, Alaska, showing the
distribution of olfactory cues in different regions of
the creek area.
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Salmon migration depends on olfactory cues
 Navigation in the open seas depends on several sensory cues
 Magnetism, sun compass, polarized light, and odors
 The olfactory hypothesis of salmon homing: young salmon
learn the odors of the home stream

The odor is a mixture of amino acids in the water
 Salmon use olfactory cues to locate the mouth of the river in
which they hatched


Following a chemical trail to the tributary where they hatched
If they choose the wrong branch, they return to the fork and
swim up another branch
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Mosaic model of avian olfactory navigation
 Pigeons form a mosaic map of environmental odors
within a radius of 70–100 kilometers of their home loft



Some of this map takes shape as young birds experience
odors at specific locations during flight
More distant features of the map are filled in as wind
carries faraway odors to the loft
The bird associates each odor with the direction of the
wind carrying it
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Gradient model of olfactory navigation
 Assumes that there are stable gradients in the intensity
of one or more environmental odors
 Wherever it was, the bird determines the strength of the
odor and compares it to the remembered intensity at the
home loft
 The gradient model demands that the bird make both
qualitative and quantitative discriminations

The mosaic model requires only that the bird make
qualitative discriminations among odors
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Distorting the olfactory map
 Manipulating olfactory information distorts the bird’s
olfactory map



Deflecting wind by wooden baffles makes it seem that odors
come from another direction
A pigeon forms a shifted olfactory map
But, the shift in orientation might be due to something other
than a distorted olfactory map
 The baffles also deflect sunlight, and change the sun
compass
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 The results of an
experiment that
manipulated a pigeon’s
olfactory information.
 (a) the experimental
pigeons were kept in a
loft that was exposed to
natural odors, as well as
to a breeze carrying the
odor of benzaldehyde
from a source northwest
of the loft.
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Depriving birds of their sense of smell
 Olfaction plays an important role in pigeon homing
 Anosmic pigeons (birds deprived of their sense of
smell) are less accurate in their initial orientation

And fewer return home from an unfamiliar, but not
from a familiar, release site
 The procedures do not affect the birds’ motivation to
return home

Anosmic pigeons home as well as control pigeons when
they are released from familiar sites
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Electrical cues and electrolocation
 Electrical cues have many uses for those organisms that
can sense them


Predators use electrical cues from organisms to detect prey
Electrical fields generated by nonliving sources (i.e. ocean
currents, waves, tides and rivers) provide cues for
navigation
 There is no evidence that migrating fish such as salmon,
shad, herring, or tuna are electroreceptive

But electrical features of the ocean floor may help guide the
movements of bottom-feeding species (i.e. dogfish shark)
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Some aquatic species have electric organs
 That generate pulses, creating electrical fields used in
communication and orientation
 The electric organs located near the tail of weak electric
fish generate brief electrical pulses



Creating an electrical field around the fish - the head acts
as the positive pole and the tail as the negative pole
Nearby objects distort the field
These distortions are detected by electroreceptors in the
lateral lines on the sides of the fish
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 小口彎頜 象鼻魚(Campylomormyrus phantasticus)
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Electrolocation is useful
 In muddy water or in fish that are
active at night
 In distinguishing between living
and nonliving objects in the
environment


An object with greater conductivity
than that of water (i.e. another
animal) directs current toward itself
Objects that are less conductive (i.e.
a rock) deflect the current away
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Fish use electrical fields to explain their
environment
 Distortions in the electrical field create an electrical
image of objects



Telling a fish a great deal about its environment
Varies according to the location of the object
The location of the image on its skin tells the fish where
the object is located
 The fish performs a series of movements close to the
object under investigation

To provide sensory input that helps the fish determine
the object’s size or shape
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Summary
 Navigational strategies are grouped into three levels
Piloting, compass orientation, true navigation
Vector navigation: an inherited program that tells a bird to fly
in a given direction for a certain length of time
Path integration: memorizing direction and distance on the
outward journey and use of a compass to travel directly home
True navigation requires a map and a compass
Visual cues are: landmarks, the sun, stars, moon and
polarization
Animals must learn to use the sun as a compass






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Summary
 Birds learn that the center of celestial rotation is north
 The earth’s magnetic field provides cues for




orientation: polarity, inclination, and intensity
Animals develop a detailed magnetic map with
experience
Two types of magnetoreceptors: light dependent and
deposits of magnetite
Some species use olfactory cues for orientation during
homing
Some aquatic species can use electrical fields or
organs for navigation and communication
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