Tag Archives: magnetic navigation

loggerhead turtle swimming

Sea turtles use Earth’s magnetic field like a GPS to find their birthplace

Although they might not have seen or been to their nesting grounds for decades, loggerhead turtles (Caretta caretta) know how to come back home with impressive accuracy rivaling man-made GPS. Now, a new study found just how exactly the turtles manage this feat: they use Earth’s magnetic field to navigate across miles and miles.

loggerhead turtle swimming

Credit: Public Domain.

For years, the loggerheads swim in loops from their nesting sites in North Carolina and Florida to North Africa. Despite the vast distances they cover, the turtles always manage to find their way home, returning to their nest beaches within about 40 to 50 miles of where they were originally born.

“Loggerhead sea turtles are fascinating creatures that begin their lives by migrating alone across the Atlantic Ocean and back,” says Kenneth Lohmann, professor of biology at the University of North Carolina at Chapel Hill.

“Eventually they return to nest on the beach where they hatched—or else, as it turns out, on a beach with a very similar magnetic field.”

According to researchers at the University of North Carolina, the loggerheads employ so-called geomagnetic imprinting to navigate their surroundings — the same process employed by some birds and fish. According to the team of researchers, the turtles can sense both the magnetic field’s intensity and inclination angle.

The scientists came to this conclusion after studying the genetic makeup of more than 800 Florida loggerheads. They showed that the turtles that nest on beaches with similar magnetic signatures were also more genetically similar than turtles that nest on beaches that were physically close to each other. Usually, you’d expect animals that are born geographically close to one another to be more related than those conceived at geographically distant locations — but the opposite was true here.

Not only was the variation of Earth’s magnetic field around a nesting site a better predictor of genetic differentiation than geographic distance, it was also a better predictor than typically important environmental conditions, such as beach temperature.

Baby loggerhead. Credit: Maxpexel.

Baby loggerhead. Credit: Maxpexel.

Although the study’s findings are limited since they’re based on genetic data, rather than experimental evidence, a more definite study is not really an option. Loggerheads take about 20 years to become sexually active and reproduce, and only 1 in 1,000 hatchlings make it to this age. It’s just unrealistic to run such an experiment for this long. But, at the end of the day, you don’t need things to be definitive for them to be evident.

Conservation efforts should consider the importance of a beach’s magnetic field for attracting loggerhead sea turtles. For instance, sea walls, power lines, and large beachfront buildings are just a few examples of perturbing factors that may alter the magnetic fields that turtles encounter.

“This is an important new insight into how sea turtles navigate during their long-distance migrations. It might have important applications for the conservation of sea turtles, as well as other migratory animals such as salmon, sharks, and certain birds,” Lohmann says.

The findings appeared in the journal Current Biology.

Humpback Whale

Humpack whales flawless natural navigation studied

Humpback Whale

A recently published study 8 years in the making reveals the uncanny ability humpback whales have of following seemingly perfect straight paths for weeks at a time. The navigational precision of humpback whales cannot be explained by known theories.

Humpback whales feed during the summer near polar oceans and migrate to warm tropical oceans for the winter, where they mate and calves are born. This means that during a year a single humpback whale can easily amass 10,000 miles worth of return journeys, making them one of the most farthest migrating animals on Earth. Their migrating paths are perfectly straight, sometimes deviated only by a few degrees, fact that poised researchers to study them and see exactly what mechanism compels the huge watery mammals to become such precise navigators.

Researchers from the University of Canterbury, in Christchurch, tracked 16 radio-tagged whales as they migrated thousands of miles north from the South Atlantic and South Pacific with unswerving accuracy, often covering more than 600 miles but deviating off course by less than one degree.

“Such remarkable directional precision is difficult to explain by established models of directional orientation,” the researchers, led by Travis Horton from the University of Canterbury, wrote in the Royal Society journal Biology Letters.

Each animal was tagged with a special positioning device which attached to the whale from four weeks to seven months before falling out, transmitting precise position data and provided one of the most detailed sets of long-term migratory data for humpbacks ever collected.

Most long-distance traveling animals are believed to navigate using an internal compass that relies either on the earth’s magnetic field or the position of the sun. However, the scientists wrote, “it seems unlikely that individual magnetic and solar orientation cues can, in isolation, explain the extreme navigational precision achieved by humpback whales.”

They instead added, “The relatively slow movements of humpback whales, combined with their clear ability to navigate with extreme precision over long distances, present outstanding opportunities to explore alternative mechanisms of migratory orientation.”

Earth’s magnetism varies too much to explain the whales’ arrow-straight patterns, and you can’t really rely on solar navigation when navigating through water.

“Humpback whales are going across some of most turbulent waters in the world, yet they keep going straight,” said environmental scientist Travis Horton of the University of Canterbury, whose team will publish their findings April 20 in Biology Letters. “They’re orienting with something outside of themselves, not something internal.”

Horton suspects humpbacks rely on both mechanisms, and perhaps the position of the moon or stars. John Calambokidis of the Cascadia Research Collective, suggested a fourth mechanism for steering: long-distance songs that can carry for hundreds or thousands of miles underwater, and may provide navigational cues or help migrating whales coordinate their movements.

“These whales are clearly using something more sophisticated to migrate than anything we’ve surmised,” said Calambokidis. “I’m really looking forward to seeing what this team does next.”

Prepared to see, correction, hear something really amazing? Check out the video below.

UPDATE: a recent study has finally proven that sockeye salmon indeed rely on magnetic field to guide itself back to the freshwater stream of their birth – a trait that’s believed to be also used by the humpbacked whale.