Navigation

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migratory & nonmigratory animals both need navigation

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migrating- for unfamiliar enviro's

nonmigrating- need it to move about in home area.

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homing

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the pigeon has a remarkable ability to find its way back to its home site when displaced into areas it has never visited before.

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Method:

eliminate or disrupt a sensory system that is presumably important in navigation

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Charles Walcott - strapped magnets to the heads of pigeons, confusing their magnetic sense. This treatment disrupted the navigation of pigeons under some circumstances, suggesting that the magnetic sense was a significant factor in the birds' navication

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Method:

Test an animal's ability to nacigate after being moved to a different location.

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Wehner & Srin- displaced desert ants where the ants had traveled a certain distance from their nest and were beginning to return to their nest. the ants then traveled a distance and in a direction that would have been appropriate had tehy not been displaced.

Thus, the researchers concluded that the ants did not rely on landmarks to find their nest but used some other mechanism that gave them a sense of direction & distance.

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Method:

Expose animals to artificial conditions, such as a planetarium in which the apparent pattern of stars may be manipulated.

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EGF Sauer- placed warblers in a planetarium and reversed the normal pattern of stars. The warblers tended to orient in the direction opposite to that of their normal migration, suggesting that some birds are able to use the pattern of stars as a compass

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Method:

Look at the correlation b/t natural disruptions (such as magnetic storms) & disruptions in navgation.

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Frei found that during magnetic storms, pigeons tend to head off in a direction different from that appropriate for returning to their loft.

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Dead Reckoning

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involves estimating direction and distance to a goal, obtaining measures of the distance and direction traveled at different points along the journey, calculating present position @ each point, and then making appropriate adjustments in the direction headed. This method is particularly useful when an animal is traveling over or in open water devoid of landmarks.

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D.R. cont'd.

Once an animal obtains its initial orientation...

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-able to stay on c ourse/continue in the same direction for a period of time.
-even if the animal veers from its set course to avoid an obstacle, it is able to adjust in such a way that it returns to the correct course without using external cues>>This ability is facilitated by an INTERNAL INERTIA SYSTEM, a system that indicates the degree of a turn and allows the animal to reorient with considerable precision.

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What does the effectiveness of a dead reckoning system depend on?

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- the effectiveness of the internal inertial system
-the ability of flying or swimming animals to compensate for wind or current
-the distance the animals must travel using the dead reckoning system exclusively
-t he accuracy of the initial reading of direction

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D.R. Continued.

DESERT ANT

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-remarkable ability to use a type of dead reckoning system
-ant makes longgg journey of up to 100 meters away from its nest in search of food...after finding food, it heads directly for the nest and travels to within a few meterse of the nest
at this point the ant begins searching movements that shortly bring it to the oening of the nest. -apparently the ant "calculates the direction it must head as well as the distance that must be traveled on the basis of angles of turns and the time spent moving in each direction.

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Clock-Shifting

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expose the birds to shifting lifhgt and dark periods out of phase with those in the real world.when taken from the room and placed in sunlight, the pigeons oriented improperly toward their home loft, flying at an angle to the sun that was off by 6 hrs.

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Sun as a compass

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-North American birds caged in the outdoors consistentlyy orient in t he direction of their normal migration (that is, they flutter in a northerly direcftion in the spring and in a southerly direction in the fall)
-if the birds are placed indoors in artificual light, they flutter in various directions without specific orientaiton.

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Garden Warblers

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-special interest to researachers bc they normally fly southwest toward the Straits of Gibraltar for 2 months and then turn and fly southeast for 2 months toward central & southern Africa.
-Will theese birds change their direction of migratory restlessness if they are caged during their normal period of migration? --YES. caged garden warblers mimic the orientation of the migrating birds , fluttering in a southwesterly direction of the migrating birds, fluttering in a southwesterly direction for the 1st 2 months, then in a southeasterly direction for the next 2. It seems that there is a bio. clock mechanism that signals the birds to orient in the new direction after a certain period.

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Azimuth

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-amount of horizontal displacement
-the rate of this is different depending on the time of day, season, and the latitude.
-if a honeybee assumed that the amount of change was the same in every hr or every season/latitude, it would make significant errors in its nacigation.
-The honeybee is able to compensate for differences in the rate of azimuth change in naviaging its return to the hive.
-James Gould caputred bees & held them for 2hrs. released bees, measured angle of flight. - his hypothesis was that the bees would "calculate" their angle of flight on the basis of info they received just before their incarceration. if this is correct, the bees should be slightly inaccurate in their orientation bec t he sun moves across the sky faster during the pd of 11 and 1 than it does just before 11.
-the bees predicted inaccuracy was very c lose to that actually observed, so hypothesis was confirmed.
-how did bees deal with inaccuracy? they were able to adjust their navigational error after they were set free and could again observe the suns movement.
-bees take periodic readings of the rate of movement of the sun when tehy are able to see the sun. they then base their estimates on those readings. . they can readjust if they cannot see the sun for a pd of time.

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Polarized Light

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-pattern of polarization shifts in a predictable way as the sun moves across the sky--so animals sensitive to polarized light receive info about the position of the sun if they can see a patch of blue sky.
-honeybees are able to use the sun as a compass even on party cloudy days

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Another advantage to polarized light

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-natural light strongly polarized at sunset, and there is a band of maximal polarization that runs north to south as the sun sets in the west. Thus, the many birds that begin their migratory movements ast sunset may use the pattern of polarized light at sunset to set their direction of flight.
-birds DO use cues from polarized light in orientation.

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The Pattern of Stars

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-many species navigate by the pattern of the stars
-Stephan Emlen- experimented w/ indigo buntings...selectively shifting certain patterns of stars
-Found that birds do not respond to the total pattern of stars, but TO PATTERNS WITHIN 35 DEGREES OF THE CELESTIAL

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The Moon

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only visible on 1/2 the days, so few animals evolved to use it as a compass.
-Exception: Talitrus Saltitor (beach hopper)

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Earth's Magnetic Field

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-magnetareceptors found in many animals
-Walcott's classic exp- pigeons magnetic sense was disrupted - demonstrates effects of magnetism on bird orientation. this disruption only occured on cloudy days. the magnetically disoriented birds oriented correctly when released on sunnydays. (PIGEONS USE SUN FIRST, IF NOT POSSIBLE THEN THEY USE MAGNET)

-marine animals also sensitive to mag. cues.- loggerhead turtles indicate that when surrounding magnetic field is experimentally reversed, turtles reverse their direction of orientation.

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Landmarks

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-visual, auditory, olfactory as "maps" to recognize the appropriate general area at the end of the journey

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Visual Landmarks

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-prominent geo. features
-pigeons familiar with area return home more quickly than birds that do not know area.
-young first leave nest-they get randomly fly around to learn landmarks.
-younger depend on older
-flying V : allows change in the flight pattern of individual birds which may reflect some knowlege of the migratory route to be communicated to the other birds.
-Not important in qqua. animals

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Acoustic Landmarks

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-some birds can recognize low frequency sounds like surf and wind to detect shorelines/forests
-Bats: echos. Dolphins too to some extent

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Chemical Cues

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Some animals are able to discriminate among diff. levels of concentration of a particular checmical substance.

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Homing in Salmon

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- Hasler & Larson
- young learn distinctive checmical cues associated w. water from particular tributatries and use these cues in their well developed homing response as adults
-without the use of olfactory cues (they plugged nose of fish) the fish were unable to find the tributary where they hatched .
-they can differentiate between odors of other streams.

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Homing in Sea Turtles

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-South America-Ascension Island=2000 miles
-they get carried away from Ascension Island to S.A. by equatorial current.
-Return few yrs later, they follow the countercurrent to get home.
-can also be explained chemically: turtles surface to breathe, they smell the current's chemical cues. (ocean currents have distinct chemical signature)
-they learn these cues when they 1st hatch.
-Why migrate so far if there are good nesting places in S.A.? it may be that mig. pattern established when S.A. and Ascension were closer together. tendency to migratae in this pattern survived.

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Olfactory Cues in Pigeons?

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-inconclusive
-they need to integrate olfactory info with other types of information in order to home.