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23 Cards in this Set
- Front
- Back
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What two types of information can the earth's magnetic field provide?
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- Compass sense (maintain a heading with respect to compass direction)
- Magnet map (determine position relative to destination) |
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How does the inclination angle of the earth's magnetic field vary with latitude?
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0 at the equator, 90 degrees at the poles.
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Water are lines of equal magnetic field inclination angle called?
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Isoclinics
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What features of the earth's magnetic field might turtles detect?
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Inclination angle
Intensity Local field anomalies (due to magnetic minerals in the earth’s crust). |
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What do we mean when we say that turtles have a "magnetic map"?
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In the broadest sense, any information that specifies the direction an animal needs to turn at a given point in its journey. Or, could mean that they know where they are relative to a target. Not necessarily a "picture".
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Are juveniles capable of map based orientation and how do we know?
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and when displaced, display orientation toward a goal (i.e. returning to foraging area); thus, can be said to be capable of map-based orientation. Juveniles placed in a tank surrounded by a coil system; when experiencing a field characteristic of the area north of the fg, turtles turned south and so forth.
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What is magnetic waypoint navigation?
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Unproven idea that adult turtles might navigate by learning the direction they must turn at any particular “magnetic waypoint” (“turtles would only need to recognize a limited number of specific fields rather than having to learn the pattern of magnetic variation over an extended geographic region.”
- (one possibility is that young loggerheads may initially navigation by detecting magnetic field inclination and intensity, but later, as they learn the area, may make migrations via a series of waypoints). |
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What is "swimming the isoline"
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unproven idea that adult turtles may swim til they intersect an isoline, then follow it to their destination.
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what is coastal orientation?
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unproven idea that adult turtles may find the continent, and then swim north or south along the coast until they encounter the inclination angle or intensity characteristic of their destination.
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what is it called when a magnetic field changes over time.
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Secular variation
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How do adult turtles navigate?
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exploit multiple cues - including but not limited to magnetic orientation.
Magnetic fields vary regionally - thus, navigational strategies may also differ. |
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What happens when magnets are attached to the heads of sea turtles?
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they can still navigate, but not as well. suggests the influence of multiple cues. Might include wind-bourne cues...
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How do hatchlings find the water?
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slope (in the absence of other cues)
light unobstructed horizon |
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How do hatchlings initially orient upon reaching the water?
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Into the waves (based on accelerations).
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How do hatchlings respond to magnetic fields. Is this learned or instinct?
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"set" their magnetic compass based on initial angle of crawling or swimming (learned).
Later, swim south when exposed to magnetic fields at the north of the gyre, etc. (instinct). |
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What are lines of equal magnetic field intensity called?
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Isodynamics
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How do nesting turtles locate Ascension Islands after displacement?
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Wind-borne cues (turtles displaced down-wind were able to relocate the island much more quickly and directly.
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When do magnets need to be applied in order to affect migration?
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Either during or prior (even when then removed).
Magnets applied prior may disrupt magnetic receptors, or prevent turtles from figuring out displacement and direction of transport. |
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What new study has been conducted to elucidate role of magnetic orientation in adult turtles?
What was the method? |
Luschi et al. 2007. Marine turtles use geomagnetic cues during open sea migration.
Displace adult females from nesting site, released with three magnetic treatments. |
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Why was the result of Luschi's recent displacement experiment different?
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Didn't put satellite transmitters on head. this might have disrupted orientation of "control" turtles
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What might be some alternatives to magnetic orientation?
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Celestial navigation, wave direction, olfactory cues.
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What was the original experiment wherein turtles were fitted with satellite transmitters and magnets before their return migration from Ascension to Brazil?
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Papi et al. 2000. Open sea migration of magnetically disturbed sea turtles. J. Exp. Biol.
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Who carried out the displacement experiments on Ascension Island turtles (displacing females from their nesting beach)?
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Luschi
Akesson Wind-borne cues: Hays (Island finding ability of marine turtles. 2003. Biology Letters |
