Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
23 Cards in this Set
- Front
- Back
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 |