scholarly journals ACQUISITION OF MAGNETIC DIRECTIONAL PREFERENCE IN HATCHLING LOGGERHEAD SEA TURTLES

1994 ◽  
Vol 190 (1) ◽  
pp. 1-8 ◽  
Author(s):  
K Lohmann ◽  
C Lohmann
Keyword(s):  
Magnetic Field ◽  
Visual Cues ◽  
Laboratory Experiments ◽  
Sea Turtles ◽  
Magnetic Orientation ◽  
Loggerhead Sea Turtles ◽  
Preferred Direction ◽  
Open Sea ◽  
Directional Preference ◽  
The Magnetic Field

During their natal migration, hatchling loggerhead sea turtles (Caretta caretta L.) establish courses towards the open ocean and maintain them after swimming beyond sight of land. Laboratory experiments have demonstrated that swimming hatchlings can orient using the earth's magnetic field. For the magnetic compass to function in guiding the offshore migration, however, hatchlings must inherit or acquire a magnetic directional preference that reliably leads them towards the open sea. On land, hatchlings find the ocean using light cues associated with the seaward horizon. To determine whether turtles might acquire a preference for a specific magnetic direction on the basis of such cues, we studied the magnetic orientation of turtles initially exposed to light from either magnetic east or west. Hatchlings that had been exposed to light in the east subsequently oriented eastward when tested in darkness, whereas those that had been exposed to light in the west swam westward. Reversing the magnetic field resulted in a corresponding shift in orientation, indicating that the turtles were orienting to the ambient magnetic field. These results demonstrate that light cues can set the preferred direction of magnetic orientation by loggerhead hatchlings. We therefore hypothesize that hatchlings initially establish a seaward course using visual cues available on or near land, then maintain the course using magnetic cues as they migrate into the open sea.

scholarly journals Magnetic orientation by hatchling loggerhead sea turtles (Caretta caretta)

1991 ◽  
Vol 155 (1) ◽  
pp. 37-49 ◽  
Author(s):  
K. J. Lohmann
Keyword(s):  
Magnetic Field ◽  
Laboratory Experiments ◽  
Caretta Caretta ◽  
Sea Turtle ◽  
Magnetic Orientation ◽  
Complete Darkness ◽  
Loggerhead Sea Turtles ◽  
Loggerhead Sea Turtle ◽  
The Earth ◽  
The Magnetic Field

Laboratory experiments were conducted to test the ability of loggerhead sea turtle hatchlings (Caretta caretta L.) to orient using the magnetic field of the earth. Hatchlings were tethered to a rotatable lever-arm apparatus which tracked swimming orientation in complete darkness. Hatchlings tested in the earth's magnetic field were nonrandomly oriented with a mean angle of 42 degrees; those tested under an earth-strength field with a reversed horizontal component were also nonrandomly oriented, but with a mean angle of 196 degrees. The distributions under the two magnetic field conditions were significantly different, indicating that loggerhead sea turtle hatchlings can detect the magnetic field of the earth and use it as a cue in orientation.

scholarly journals Orientation and open-sea navigation in sea turtles

1996 ◽  
Vol 199 (1) ◽  
pp. 73-81 ◽  
Author(s):  
K Lohmann ◽  
C Lohmann
Keyword(s):  
Magnetic Field ◽  
Visual Cues ◽  
Sea Turtles ◽  
Positional Information ◽  
Sea Turtle ◽  
Compass Orientation ◽  
Loggerhead Sea Turtle ◽  
Open Sea ◽  
Nesting Beaches ◽  
Field Inclination

Loggerhead sea turtle hatchlings (Caretta caretta L.) emerge from underground nests, scramble to the sea and begin a transoceanic migration by swimming away from their natal beach and into the open ocean. Evidence suggests that hatchlings sequentially use three different sets of cues to maintain orientation during their initial migration offshore. While on the beach, hatchlings find the ocean by crawling towards the lower, brighter seaward horizon and away from the dark, elevated silhouettes of vegetation and dunes. Upon entering the ocean, turtles initially orient seawards by swimming into waves, which can be detected as orbital movements from under water. Laboratory experiments have demonstrated that turtles can transfer a course initiated on the basis of waves or visual cues to a course mediated by a magnetic compass. Thus, by setting a magnetic course on the basis of nearshore cues that indicate the seaward direction, hatchlings may continue on offshore headings after entering deep water beyond sight of land. Sea turtles may use the earth's magnetic field not only as a cue for compass orientation but also as a source of world-wide positional information. Recent experiments have demonstrated that loggerheads can detect subtle differences in magnetic field inclination and intensity, two geomagnetic features that vary across the surface of the earth. Because most nesting beaches and oceanic regions are marked by a unique combination of these features, these findings raise the possibility that adult sea turtles navigate using a bicoordinate magnetic map.

scholarly journals Lepton-driven Nonresonant Streaming Instability

2021 ◽  
Vol 923 (2) ◽  
pp. 208
Author(s):  
Siddhartha Gupta ◽  
Damiano Caprioli ◽  
Colby C. Haggerty
Keyword(s):  
Magnetic Field ◽  
Laboratory Experiments ◽  
Magnetized Plasma ◽  
Ion Current ◽  
Pulsar Wind Nebulae ◽  
Particle In Cell ◽  
Streaming Instability ◽  
Electrons And Positrons ◽  
Pulsar Wind ◽  
The Magnetic Field

Abstract A strong super-Alfvénic drift of energetic particles (or cosmic rays) in a magnetized plasma can amplify the magnetic field significantly through nonresonant streaming instability (NRSI). While the traditional analysis is done for an ion current, here we use kinetic particle-in-cell simulations to study how the NRSI behaves when it is driven by electrons or by a mixture of electrons and positrons. In particular, we characterize the growth rate, spectrum, and helicity of the unstable modes, as well the level of the magnetic field at saturation. Our results are potentially relevant for several space/astrophysical environments (e.g., electron strahl in the solar wind, at oblique nonrelativistic shocks, around pulsar wind nebulae), and also in laboratory experiments.

Satellite tracking of migrating loggerhead sea turtles (Caretta caretta) displaced in the open sea

2003 ◽  
Vol 143 (4) ◽  
pp. 793-801 ◽  
Author(s):  
P. Luschi ◽  
G. R. Hughes ◽  
R. Mencacci ◽  
E. De Bernardi ◽  
A. Sale ◽  
...  
Keyword(s):  
Sea Turtles ◽  
Caretta Caretta ◽  
Satellite Tracking ◽  
Loggerhead Sea Turtles ◽  
Open Sea

scholarly journals On Special Features of Non-Thermal Solar X Radiation above 10 keV

1972 ◽  
Vol 14 ◽  
pp. 761-762
Author(s):  
G. Elwert ◽  
E. Haug
Keyword(s):  
Magnetic Field ◽  
Angular Distribution ◽  
Power Law ◽  
Impulsive Phase ◽  
X Rays ◽  
Energetic Electrons ◽  
X Ray ◽  
Preferred Direction ◽  
Field Lines ◽  
The Magnetic Field

The polarization and angular distribution of solar hard X radiation above 10 keV was calculated under the assumption that the X rays originate as bremsstrahlung from energetic electrons moving in a preferred direction. The source electrons are supposed to have a power-law spectrum. These conditions are to be expected in the impulsive phase of an X-ray burst. The spiral orbits of the electrons around the magnetic field lines are taken into account.

The case for light-dependent magnetic orientation in animals

1999 ◽  
Vol 202 (8) ◽  
pp. 891-908 ◽  
Author(s):  
M.E. Deutschlander ◽  
J.B. Phillips ◽  
S.C. Borland
Keyword(s):  
Magnetic Field ◽  
Physiological Model ◽  
Magnetic Compass ◽  
Magnetic Orientation ◽  
Orientation Behavior ◽  
Long Wavelength ◽  
Alternative Hypotheses ◽  
Magnetite Particles ◽  
The Magnetic Field ◽  
Effect Of Light

Light-dependent models of magnetoreception have been proposed which involve an interaction between the magnetic field and either magnetite particles located within a photoreceptor or excited states of photopigment molecules. Consistent with a photoreceptor-based magnetic compass mechanism, magnetic orientation responses in salamanders, flies and birds have been shown to be affected by the wavelength of light. In birds and flies, it is unclear whether the effects of light on magnetic orientation are due to a direct effect on a magnetoreception system or to a nonspecific (e.g. motivational) effect of light on orientation behavior. Evidence from shoreward-orienting salamanders, however, demonstrates that salamanders perceive a 90 degrees counterclockwise shift in the direction of the magnetic field under long-wavelength (>=500 nm) light. A simple physiological model based on the antagonistic interaction between two magnetically sensitive spectral mechanisms suggests one possible way in which the wavelength-dependent effects of light on the salamander's magnetic compass response might arise. Assuming that the wavelength-dependent characteristics of the avian magnetic response can be attributed to an underlying magnetoreception system, we discuss several hypotheses attempting to resolve the differences observed in the wavelength-dependent effects of light on magnetic orientation in birds and salamanders. By considering the evidence in the context of photoreceptor- and non-photoreceptor-based mechanisms for magnetoreception, we hope to encourage future studies designed to distinguish between alternative hypotheses concerning the influence of light on magnetoreception.

scholarly journals GEOMAGNETIC ORIENTATION OF LOGGERHEAD SEA TURTLES: EVIDENCE FOR AN INCLINATION COMPASS

1993 ◽  
Vol 182 (1) ◽  
pp. 1-10 ◽  
Author(s):  
P. Light ◽  
M. Salmon ◽  
K. J. Lohmann
Keyword(s):  
Magnetic Field ◽  
Field Component ◽  
Sea Turtles ◽  
Magnetic Compass ◽  
Magnetic Field Component ◽  
Vertical Magnetic Field ◽  
Earth’S Magnetic Field ◽  
Loggerhead Sea Turtles ◽  
Earth's Magnetic Field ◽  
Inclination Compass

Recent experiments have demonstrated that hatchling loggerhead sea turtles can orient using the earth's magnetic field. To investigate the functional characteristics of the loggerhead magnetic compass, we tested the orientation of hatchlings tethered inside a circular arena surrounded by a coil system that could be used to reverse the vertical and horizontal components of the ambient field. Hatchlings tested in darkness in the earth's magnetic field were significantly oriented in an eastward direction. Inverting the vertical magnetic field component resulted in an approximate reversal of orientation direction, whereas reversing both the vertical and horizontal components together did not. The hatchlings failed to orient in a horizontal field of earth-strength intensity. These results provide evidence that the magnetic compass of loggerheads is an inclination (axial) compass, functionally similar to that of birds.

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