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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/
大學部 生態學與保育生物學學程 ( 必選 ) 2010 年 秋冬
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 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 levels1. Piloting ( 引導 )
2. Compass orientation ( 羅盤定位 )
3. True navigation ( 真領航 )
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 8
Compass orientation
Displaced birds did not reach their normal destination and ended up in ecologically unsatisfactory places
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 11
→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.
←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.
Ayo 教材 (動物行為學 2010) 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)
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 16
An animal that finds its way by using true navigation can compensate for experimental relocation and travel toward the goal.
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 23
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
Ayo 教材 (動物行為學 2010) 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 )
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 28
A clock-shift experiment demonstrates time-compensated sun compass orientation.
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 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 )
Ayo 教材 (動物行為學 2010) 31
Indigo Bunting
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.
The Indigo Bunting, Passerina cyanea, is a small seed-eating bird in the family Cardinalidae.
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 33
The stars rotate around Polaris, the North Star. The positions of stars in the northern sky during the spring are shown here.
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 36
The orientation of indigo buntings to a stationary planetarium sky after exposure to different celestial rotations.
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 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.
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 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.
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 46
The earth’s magnetic field.
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 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.
Ayo 教材 (動物行為學 2010) 50
Birds orient using the inclination angle
In the laboratory, European robins oriented in the proper direction even without visual cues
Ayo 教材 (動物行為學 2010) 51
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.
Birds orient using the inclination angle
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 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”
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 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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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
Ayo 教材 (動物行為學 2010) 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
Ayo 教材 (動物行為學 2010) 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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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.
Ayo 教材 (動物行為學 2010) 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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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
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.
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。
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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 light-
dependent 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