We’ve heard of sailors using the stars to navigate their ships, long before they started using a compass.
But did you know, sea turtles have an inbuilt compass that guides them back to where they were born? They return to their ‘home’ beaches to reproduce, and in doing so, kickstart many more cycles of travel.
The study by the University of North Carolina focused on loggerhead sea turtles, which cover thousands of miles periodically, guided by the Earth’s magnetic field.
Sea Turtles And Their Migration
Loggerhead sea turtles get their names from their larger-than-normal heads. They are found across the world often near coastal areas and live for about 50 years in the wild.
However, poaching, pollution, and even tourism have placed them on the endangered list for the past three decades. Their primary diet consists of shellfish, crabs, and even seaweeds. Among the largest turtles on earth, adult loggerheads typically measure just under a meter in length and weigh almost 115 kg on average.
While male turtles rarely leave the water, the females often cross thousands of miles to return to the beaches where they were born. These beaches are perfect for their needs - accessible, with few predators, and the perfect climate for nesting and hatching. Biologists call this behavior ‘natal homing’ – going back to their birthplace.
How Do They Do It?
Scientists believe sea turtles track their home turf’s magnetic signatures. Every location has unique magnetic coordinates which the hatchling turtles register.
When they migrate, they leave their "birth beaches" and follow ocean currents to different regions. Later, as adults, when they are ready to reproduce, they automatically go back home. This is called geomagnetic imprinting – which means absorbing the magnetic signatures of the surroundings shortly after birth.
Now, the Earth’s natural movements often cause its molten inner core to shift around. Think of it as liquid metal sloshing about. This leads to small changes in the magnetic field.
Researchers from the University of North Carolina studied 19 years of data on the nests of loggerhead turtles in Florida, the largest population in North America. They found that when magnetic signatures of beaches moved closer to each other, the turtles’ nests were also densely packed in that region. And when the magnetic signatures moved away, each region had fewer turtles’ nests!
While there is no explanation for how they do it, scientists believe small magnetic particles in the turtles’ brains help them follow the Earth’s magnetic field.
