project news

Animal magnetism or turtle pragmatism?

News item submitted by Ben Margerison
News item dated 28 Feb 2011


It has been known for a while that many migratory species are able to navigate long distances using cues from the earth’s magnetic field. Spiny lobsters, many species of bird and several species of marine turtle have been shown to be able to deduce their position relative to the magnetic field of the earth in a latitudinal sense (north to south) and several species are thought to be able to navigate using changes in magnetic gradients longitudinally (east to west).

The magnetic field of the earth varies far more with a change in latitude than with a change in longitude. This has meant evidence on magnetic longitudinal navigation has proven extremely hard to extract, although it most certainly appears to be an adaptation utilised in the animal kingdom. A recent study on navigation in loggerhead turtles has provided the first piece of significant evidence that such an adaptation exists

The study, undertaken by Nathan Putnam et al. from the University of North Carolina, consisted of a test on two groups of loggerhead hatchlings from Eastern Florida that had not yet swum in the ocean. One group was placed in a tank in which a magnetic field typical of that found near Cape Verde on the East side of the Atlantic was replicated. The other group was placed in a tank with a magnetic field typical of that found near Puerto Rico on the western side of the Atlantic. The latitude of the replicated magnetic field was identical for both groups. The two groups were shown to instinctively swim in a significantly different direction to one another with the direction being characteristic of the migratory pattern of the species.

This is the first documented case of a species in possession of both a latitudinal and longitudinal magnetic map. For hundreds of years humans struggled to navigate accurately, with longitudinal navigation posing a particular problem. Precise navigation is a relatively modern development for humans, but as this fascinating study has shown, it’s something that comes wholly naturally to loggerhead turtles.

Volunteers on the Tanzania marine project recently witnessed the hatching of hundreds of green turtles, and those on the Costa Rica project recently witnessed the hatching of hundreds of Olive Ridley turtles. Although no one can know what life holds in store for these hatchlings, one thing’s for sure, they’ll always be able to find their way.