The invisible but vital imprint of turtles

Birds do it, frogs do it, #link:http://www.pnas.org/content/early/2008/08/22/0803650105:cows# do it, #link:http://www.livescience.com/42317-dogs-poop-along-north-south-magnetic-lines.html:dogs# do it, and so do sea turtles… They all use the #link:http://www.ks.uiuc.edu/Research/magsense/ms.html:earth’s magnetic field for orientation# purposes.

While birds rely on it (in part) to fly south in winter, and frogs to find the fastest way to shore in moments of danger, the creature that makes most fascinating use of the big magnet known as earth is the turtle.

You might already know that each turtle #link:http://www.unc.edu/depts/oceanweb/turtles/:returns to the beach where it hatched# to lay its own eggs. How they do it has had scientists scratching their heads for some time. Although they knew it had something to do with the magnetic field, they didn't know exactly what.

After a series of experiments, researchers at the University of North Carolina believe they have lifted the curtain on that mystery. When turtles are born the pattern of the magnetic field in their birthplace is literally #link:http://uncnews.unc.edu/2015/01/13/sea-turtles-theres-no-place-like-magnetic-home/:imprinted on them#. Albeit invisibly.

When they reach maturity and are ready to lay their own eggs, they swim along shorelines looking for the unique magnetic signature left on them when they first saw the light of day.

It becomes a little trickier if the earth’s field shifts during the turtle’s lifetime. The scientists observed that if the magnetic signatures of adjacent locations moved closer together, turtles packed into a shorter stretch of beach. By contrast, if the magnetic signature dispersed, the turtles also spread out, laying eggs in different nests along the beach.

The next mystery to solve is how they actually sense the magnetic field.