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23 Cards in this Set

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What two types of information can the earth's magnetic field provide?
- Compass sense (maintain a heading with respect to compass direction)
- Magnet map (determine position relative to destination)
How does the inclination angle of the earth's magnetic field vary with latitude?
0 at the equator, 90 degrees at the poles.
Water are lines of equal magnetic field inclination angle called?
Isoclinics
What features of the earth's magnetic field might turtles detect?
Inclination angle
Intensity
Local field anomalies (due to magnetic minerals in the earth’s crust).
What do we mean when we say that turtles have a "magnetic map"?
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".
Are juveniles capable of map based orientation and how do we know?
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.
What is magnetic waypoint navigation?
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).
What is "swimming the isoline"
unproven idea that adult turtles may swim til they intersect an isoline, then follow it to their destination.
what is coastal orientation?
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.
what is it called when a magnetic field changes over time.
Secular variation
How do adult turtles navigate?
exploit multiple cues - including but not limited to magnetic orientation.

Magnetic fields vary regionally - thus, navigational strategies may also differ.
What happens when magnets are attached to the heads of sea turtles?
they can still navigate, but not as well. suggests the influence of multiple cues. Might include wind-bourne cues...
How do hatchlings find the water?
slope (in the absence of other cues)
light
unobstructed horizon
How do hatchlings initially orient upon reaching the water?
Into the waves (based on accelerations).
How do hatchlings respond to magnetic fields. Is this learned or instinct?
"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).
What are lines of equal magnetic field intensity called?
Isodynamics
How do nesting turtles locate Ascension Islands after displacement?
Wind-borne cues (turtles displaced down-wind were able to relocate the island much more quickly and directly.
When do magnets need to be applied in order to affect migration?
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.
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.
Why was the result of Luschi's recent displacement experiment different?
Didn't put satellite transmitters on head. this might have disrupted orientation of "control" turtles
What might be some alternatives to magnetic orientation?
Celestial navigation, wave direction, olfactory cues.
What was the original experiment wherein turtles were fitted with satellite transmitters and magnets before their return migration from Ascension to Brazil?
Papi et al. 2000. Open sea migration of magnetically disturbed sea turtles. J. Exp. Biol.
Who carried out the displacement experiments on Ascension Island turtles (displacing females from their nesting beach)?
Luschi
Akesson

Wind-borne cues:
Hays (Island finding ability of marine turtles. 2003. Biology Letters