It's well known that sea turtles and some other aquatic animals exhibit what is called "natal homing," where adults return to locations at or near their birthplace to reproduce. Many descriptions of natal homing would have you believe that every turtle returns to the exact beach or even the exact spot where they were born, but in practice this sort of precision is uncommon. In most cases, sea turtles return to a geolocation near their birthplace, but this may be the next beach, the next county, or even the next state.
Exactly how sea turtles engage in natal homing is still being studied, but evidence suggests that geomagnetic imprinting, a process by which animals use magnetoreception to detect and remember the geomagnetic signature of important locations such as their natal beach or foraging grounds. Since Earth's magnetic fields are not static, the signatures that the turtles are looking for may shift during the decade-long period where juveniles are living in open ocean currents. These variations impact where the turtle actually returns to and also impact nesting site densities, as more turtles will return to places where magnetic lines converge. That is, geomagnetic imprinting draws turtles to beaches with similar signatures to their home beach, even if it's not their exact home beach. As such, locations with similar magnetic field signatures are a better predictor of genetic similarity between turtles than are the distances between nesting areas.
It is also possible that additional cues are used for greater precision once the turtle locates the general geomagnetic region. While these additional cues are not well understood in sea turtles, other aquatic animals that engage in long oceanic migrations use similar tactics. As an example, salmon are known to use olfactory cues to pinpoint their home stream.
The loggerhead turtle population is separated into subpopulations that vary genetically. Turtles born in our region that make it to adulthood generally nest in areas that are part of the Northern Recovery Unit, which encompasses GA, SC, and NC. If you look at DNA records for some turtles, you will note that they stick to nesting on Seabrook, Kiawah and Edisto beaches. Does this mean they were born on one of these three beaches? Maybe, but not necessarily. In addition to natal homing, sea turtles also exhibit what is called "nesting site fidelity," which is when a mother returns to a preferred nesting beach for multiple nests and possibly multiple nesting seasons. While this beach isn't necessarily the turtle's birthplace, it becomes its adoptive home for the purposes of nesting time and time again, which is every bit as cool as precise natal homing!
The following is a good explainer on how geomagnetic imprinting associated with natal homing works:
https://lohmannlab.web.unc.edu/geomagnetic-imprinting/
This report discusses the evidence to support geomagnetic imprinting in sea turtles and how variations in the Earth's magnetic field impact nesting site densities:
https://www.sciencedirect.com/science/article/pii/S0960982214016388
Fun Fact: A mama that nested on Seabrook Island in 2016 also nested 315 miles up the coast in Cape Hatteras in the same year! This is the farthest distance between nests for a Seabrook mama since DNA records started being kept!
