1. 導航機制(Mechanisms of Orientation and Navigation ─動物行為學 (Ethology)
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:

2. 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)
Ayo 教材 (動物行為學 2010)

3. 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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4. 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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5. 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
Piloting (引導)
Compass orientation (羅盤定位)
True navigation (真領航)
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6. 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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7. 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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8. Compass orientation
Displaced birds did not reach their normal destination and ended up in ecologically unsatisfactory places
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9. 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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10. 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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11. ←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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12. 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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13. 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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14. 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
It is set again by the next outward journey
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15. 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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16. An animal that finds its way by using true navigation can compensate for experimental relocation and travel toward the goal.
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17. 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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18. 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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19. 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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20. 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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21. 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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22. 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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23. The sun follows of predictable path through the sky that varies with latitude and season.
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24. 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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25. 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
Starling (歐掠鳥)
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26. 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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27. 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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28. A clock-shift experiment demonstrates time-compensated sun compass orientation.
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29. 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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30. 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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31. 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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32. 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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33. The stars rotate around Polaris, the North Star
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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34. 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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35. 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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36. The orientation of indigo buntings to a stationary planetarium sky after exposure to different celestial rotations.
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37. 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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38. 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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39. 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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40. 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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41. 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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42. 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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43. 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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44. 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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45. 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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46. The earth’s magnetic field.
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47. 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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48. 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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49. 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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50. Birds orient using the inclination angle
In the laboratory, European robins oriented in the proper direction even without visual cues
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51. 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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52. 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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53. 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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54. 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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55. 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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56. 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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57. 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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58. 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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59. 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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60. 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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61. 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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62. 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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63. 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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64. 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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65. The flight paths of pigeons in magnetic anomalies
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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66. 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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67. 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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68. 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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69. 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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70. Seeing the earth’s magnetic field. The visual field of a bird flying.
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71. 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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72. Cryptochromes Cryptochrome是一種藍光/紫外光受體，與果蠅生物鐘的控制有關。
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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73. 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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74. 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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75. 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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76. 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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77. 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 light-dependent magnetoreception process, to head in the appropriate direction
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78. 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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79. 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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80. A map of Hansen creek, Alaska, showing the distribution of olfactory cues in different regions of the creek area.
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81. 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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82. 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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83. 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
Ayo 教材 (動物行為學 2010)

84. 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
Ayo 教材 (動物行為學 2010)

85. 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.
Ayo 教材 (動物行為學 2010)

86. 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
Ayo 教材 (動物行為學 2010)

87. 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)
Ayo 教材 (動物行為學 2010)

88. 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
Ayo 教材 (動物行為學 2010)

89. 小口彎頜 象鼻魚(Campylomormyrus phantasticus)
Ayo 教材 (動物行為學 2010)

90. 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
Ayo 教材 (動物行為學 2010)

91. 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
Ayo 教材 (動物行為學 2010)

92. 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
Ayo 教材 (動物行為學 2010)

93. 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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94. 問題與討論 Japalura@hotmail.com
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Ayo 教材 (動物行為學 2010)