Migration and Navigation of the Loggerhead turtle
 Loggerheads travel thousands of miles across the Atlantic Ocean to the  circular current systems called gyres that serve as open ocean nurseries, where they stay for several years to mature. The male turtles will then migrate to their foraging areas, while the females eventually will return near their birth place to lay their eggs.
Sea turtles are using the earths magnetic field , the sun, and skylight polarization to navigate across the oceans and find specific destinations, as well as to return to the beach where they were hatched. They calibrate their built in "compass" to the horizon when they are first born and utilize the oceans waves to guide them several miles out to sea after they first enter the water. Since these turtles are sensitive to small differences in field inclination and intensity (Lohman, 1996) they can use the fields that exist at specific locations to help them navigate.
They also use those fields as markers along their journey, and detect errors in the course by changes in the angle of the magnetic field.
Metal cages are often placed over the nests to protect the eggs from predators like dogs, foxes, and especially racoons. However, some studies seem to indicate that the metal in those cages disrupts the

photo courtesy by sciencedirect.com

calibration of the turtles to the magnetic field. One option to resolve that issue is to construct cages made of non magnetic material. The lights from hotels and streets near nesting beaches can also distort the hatchlings, as they try to find their way towards the ocean, and take them inland instead. Having dimmed or no lights during hatching season can help the little turtles with their journey.
 www.nature.com/nature

Sources
Geomagnetic map used in sea-turtle navigation, by K. Lohmann, Nature|Vol 428|29 April 2004|
www.nature.com/nature
Magnetic field distortion produced by protective cages around sea turtle nests, by Irwin, Horner,Lohmann Biological Conservation 118 (2004) 117-120