Turtles Find Their Way Using Magnetic Fields

October 25, 2001

We use light, sound, pressure, temperature, smell and taste to explore the outside world. However, our senses are tuned to only a small portion of the signals in the environment. For instance, the light we can see is only a small part of the electromagnetic spectrum. Other animals make use of signals in the environment that we cannot detect without special instruments. For example, rattlesnakes can "see" infrared wavelengths with pit organs and butterflies can see ultraviolet light. Moreover, we hear only sounds that have frequencies between 20 and 20,000 Hz. Elephants can hear sounds with frequencies below 20 Hz while bats, dolphins and dogs can hear sounds with frequencies above 20,000 Hz. New research shows that sea turtles take advantage of another environmental signal that humans cannot detect: magnetic fields!

Baby loggerhead sea turtles (Caretta caretta) swim from the southeast coast of the United States into the North Atlantic Ocean where they find a warm water current called the North Atlantic gyre. The turtles follow this current for five to ten years before returning to the coast where they were born. However, if they stray away from the warm gyre, cold water will kill them. How do the turtles know where to go? How do they avoid the cold water? Scientists in the Department of Biology at the University of North Carolina, now think they know how the turtles navigate across the Atlantic Ocean and stay within the warm current.

The scientists knew that magnetic fields vary across the earth's surface. To test whether loggerhead turtles could use information about magnetic fields, the scientists placed turtle hatchlings into a pool of sea water which was surrounded by electric coils. The coil system could be adjusted to change the magnetic fields around the pool. The location of each turtle was monitored by a computer tracking system.

The direction that the turtles swam was dependent on the magnetic field.
Type of Magnetic Field Swimming Direction
Northern Florida CoastEast-Southeast
Coast of PortugalSouth
Coast north of BrazilWest-Northwest

The path the turtles swam was influenced by the different magnetic fields that the scientists provided. The directions in which the turtles swam would have kept them within the warm North Atlantic gyre. Thus, it is likely that baby sea turtles have the innate ability to detect magnetic fields and use these cues for navigation. The brain mechanisms involved in the detection of magnetic fields remain a mystery for future study.

Reference and further information about loggerhead turtles:

  1. Lohmann, K.J., Cain, S.K., Dodge, S.A. and Lohmann, C.M.F., Regional magnetic fields as navigational markers for sea turtles. Science, 294:364-366, 2001.
  2. All photographs of the loggerhead turtles on this page are used with the permission of photographer John White.

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