Leatherback sea turtles rely on a soft pink spot atop their heads that uses the sun to tell them what season it is.

Leatherback sea turtles spend most of their lives in water, with females only coming to land to lay their eggs.

Up until now, it was unknown how these creatures navigated the oceans, and how females knew when to mate and come back to shore.

Researchers from Ireland and Hawaii examined four dead turtles that were found after being killed by long-line fisheries.

They found a non-pigmented spot located on top of their heads.

Referred to as the "pink spot," this may be the key behind how the turtles know the seasons are changing.

The bone and cartilage beneath this spot is thinner than the rest of the turtle's skull, allowing sunlight to radiate through.

The sunlight reaches a specific region of the brain, known as the pineal gland.

The pineal gland acts as a biological clock, in charge of setting the turtles' seasonal behavior.

Researchers believe this method of sensing the change in sunlight and temperature during the year is used to notify the turtles when it's time to migrate.