Loggerhead Turtles Home In On Nests Magnetically
Around the world there are certain beaches that marine turtles return to each year to lay their eggs buried beneath the soft sand. Distinctive marking on some turtles show that they return to the same beach every two or three years to lay more eggs. Loggerhead turtles, for example, leave their natal beaches as hatchlings and traverse entire ocean basins before returning to nest, at regular intervals, on the same stretch of coastline where they were born. How sea turtles accomplish this natal homing has remained an enduring mystery until now. Scientists have been telling us that the turtles find the way back to the same beach by means of the earth magnetic fields. That point, while widely accepted, has not had any evidence to support the theory.There are many conservation organizations that protect turtle eggs. Some use beach watchers to locate turtles digging their nest and the location is marked. If the nest can be protected in place, it is left alone. If not the eggs are carefully removed and relocated. In most cases before the hatchings make their way to the sea, scientists will count and weight the turtles. When the turtles are ready to be release to the wild, generally at the next sun down, the hatchlings are made to crawl their way to the water. The reason given is so that the turtles can imprint the magnetic fields of the beach.
A just released study has finally added some scientific evidence that the theory may be true. A paper entitled " Evidence for Geomagnetic Imprinting and Magnetic Navigation in the Natal Homing of Sea Turtles" brings some hard data to the theory. The paper presented data on the following points:
•Sea turtle nesting density varies with slight changes in Earth's magnetic field
•Results imply that sea turtles locate nesting beaches using geomagnetic cues
•Turtles likely imprint on the unique magnetic signature of their natal beach
•Similar mechanisms may explain natal homing in diverse long-distance places of migration.
Researchers study magnetic data from along the US east coast covering 19 years. They located times and places they believe that nesting would be modified.The Earth's field shifted so that the magnetic signatures of adjacent locations along the beach moved closer together. When that happened, nesting turtles packed themselves in along a shorter stretch of coastline. In places where magnetic signatures diverged, sea turtles spread out and laid their eggs in nests that were fewer and farther between. While the means that the turtles can do that is still not known, it does add weight to the theory of magnetic imprinting.