Loggerhead sea turtles are capable of navigating using both latitudinal and longitudinal magnetic cues as demonstrated in a recent study published in the journal Current Biology. The project was led by Nathan F. Putman of the University of North Carolina.
The experiment was the first to demonstrate the existence of a bicoordinate map system in animals which can integrate both longitudinal and latitudinal information detected from Earth’s magnetic field.
Previous experiments have shown that animals are capable of determining their geographical position latitudinally using Earth’s magnetic field.
The magnetic pull decreases noticeably as one moves away from the north and south poles. Longitudinally (moving east or west), however, the detected force remains constant, while the angle varies only minimally.
The idea that animals are able to perceive both latitudinal and longitudinal differences is hard to believe. However, the ability of turtles and other migratory animals to find their exact locations over long distances with considerable accuracy suggests otherwise.
In this experiment, sea turtle hatchlings were individually placed in the center of a water pool surrounded by computerized coil systems. The coils were used to set the magnetic field felt by the turtles.
All turtles started with an initial magnetic field identical to the one the animals were exposed to when they were born.
After 10 minutes, the magnetic field was changed to either match a field similar to one near Puerto Rico or to one near the Cape Verde Islands.
These two locations lie along the same latitude, but are on opposite sides of the world. The hatchlings were given three minutes to adapt to the new field, after which each turtle’s swimming direction was recorded for the subsequent five minutes.
Results show that turtles exposed to the Puerto Rico field swam in the northeast direction, while those exposed to the Cape Verde Islands swam in the southwest direction.
Both groups were statistically significantly oriented, indicating that loggerhead turtles are capable of distinguishing between magnetic fields of different longitudes along the same latitude.
Furthermore, both groups swam towards the direction that would lead them back to the coast of North America, where most loggerhead sea turtles live as juveniles.
The directions the turtles swam in also avoided numerous natural obstacles such as the Guinea Current and southeast branch of Canary Currents between North America and the Cape Verde Islands that may have displaced the turtles off course.
The turtles’ ability to use both longitudinal and latitudinal information suggests that they use at least two distinct and varying geomagnetic characteristics of the Atlantic Ocean.
Results of this study show that turtles use a bicoordinate magnetic map in navigation — a skill long suspected but never proven in animals.
Loggerhead turtles’ internal representation of the magnetic map is unknown. It is also possible that hatchling turtles use other cues to guide their migratory route.
How animals detect both latitudinal and longitudinal differences remains unknown. In addition to magnetic bicoordinate maps, other possible sensory information includes sensitivity of biological clock to time differences, olfactory cues and infrasound.
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