Geomagnetic Navigation in Sea Turtles

How These Reptiles Use Earth’s Magnetic Field to Find Their Way

Jul 31, 2009

Sea turtles have a remarkable ability to use a "compass sense" to help them find their way to regular feeding and nesting areas.

From the moment sea turtle hatchlings make their way to the ocean for the first time, they use environmental cues to find their way into the unknown.

Scientists have learned that these ancient creatures have a highly developed “map sense” and a geomagnetic “compass sense” that enables them to navigate the sea unerringly.

How Sea Turtle Hatchlings Find Their Way to the Sea

Baby sea turtles depend on the natural environment to provide cues to help them find their way into waters to mature. Once there, they will use their more refined senses to navigate the open ocean, locate food, and eventually return to home shores to breed. But in the moments after hatching, the babies instinctively know their future home is toward the starry, open sky and unobstructed horizon.

This is the reason why the bright lights of man’s residential or business districts can have a negative effect if the hatchlings are on beaches near such lights. The turtles will mistake the lights for the night sky or horizon, and soon find themselves lost, far from the edge of the water. Hatchlings that do reach the water will eventually make their way far into the sea, and begin orienting themselves in direction and latitude using Earth’s magnetic field.

In his 2006 book Sea Turtles: An Extraordinary Natural History of Some Uncommon Turtles, author Blair Witherington writes that “a hatchling at this milestone has not only learned the magnetic feel of movement out to sea, but it has also acquired a magnetic awareness of location applicable to any of (its) travels from that point forward.”

A Sea Turtle Has A Map Sense and a Compass Sense

Studies by Kenneth Lohmann and colleagues at the University of North Carolina at Chapel Hill have been instrumental in bringing to the forefront information about the relationship between sea turtles and geomagnetic navigation. The Lohmann Lab web site explains a study of the juvenile green sea turtle’s map sense.

The results of the study showed that the turtle has a magnetic map that helps it know its position relative to a specific destination, such as feeding grounds, and may be used with the turtle’s compass—or directional—sense, as well as other environmental cues (such as the shoreline) to put itself on a course to reach that specific destination.

The Olfactory Section of the Turtle’s Brain

While researchers have long suspected that a sea turtle’s excellent sense of smell plays a role in navigation, a nasal structure called the Jacobson's organ is thought to be linked with the turtle’s geomagnetic skill. This organ is connected the olfactory bulb in the turtle’s brain. It is possible that small particles of magnetite, an iron ore, are located near the sea turtle’s nose, which help “stimulate the turtle’s brain with a sense of magnetic location,” according to Witherington.

Why Sea Turtles Must Know How to Orient Themselves

All of these advanced skills are important to sea turtles because, after hatching, they may spend up to five years floating in the ocean among various habitats specific to their species. For loggerhead turtles, the journey at sea to maturity is longer, maybe a decade. Each species of sea turtle has its preferred feeding grounds, and every female sea turtle instinctively returns to breed at the beach where she hatched—the same nesting site as her forebears. It is a part of her DNA. This faithfulness to the beach where she was born is called “natal philopatry.”

Perhaps one day researchers will know for sure all of the mysteries behind the sea turtle’s amazing instincts and navigational abilities. It is yet another example of how an animal considered ancient and perhaps simple has more advanced inner workings than man currently understands.

The copyright of the article Geomagnetic Navigation in Sea Turtles in Turtles is owned by Cheryl Kraynak. Permission to republish Geomagnetic Navigation in Sea Turtles in print or online must be granted by the author in writing.