Now, new findings by a research team headed by Drs. Kenneth and Catherine Lohmann, marine biologists at the University of North Carolina at Chapel Hill, indicate that the navigational ability of sea turtles is based at least partly on a "magnetic map" -- a remarkable ability to read geographic position from subtle variations in the Earth's magnetic field.
Previous work by the group showed that baby sea turtles can use magnetic information as a built-in compass to help guide them during their first migration across the Atlantic Ocean. Their latest studies reveal that older turtles use the Earth's field in a different, far more sophisticated way: to help pinpoint their location relative to specific target areas, the scientists say. In effect, older turtles have a biological equivalent of a global positioning system (GPS), but the turtle version is based on magnetism.
A report on experiments with juvenile green turtles appears in the April 29 issue of Nature, a scientific journal. Besides the Lohmanns, authors are Timothy Swing, a recent UNC graduate, and biology professor Dr. Llew Ehrhart and graduate student Dean A. Bagley, both of the University of Central Florida.
Working and living for a summer on the coast near Cape Canaveral, Fla., the team built a special cube-shaped magnetic coil system almost the height of a two-story house. They used the coil to reproduce the magnetic fields that exist in different areas along the southeastern U.S. coast. They also placed a pool of water in the center of the coil so that they could expose the turtles to various magnetic fields while observing the direction in which they swam.
"We captured juvenile turtles using a 400
Contact: David Williamson
University of North Carolina at Chapel Hill