Leatherback sea turtles (Dermochelys coriacea), swim all along the cool temperate waters of the western and eastern margins of the North Atlantic during the summer, foraging for jellyfish and other food. These giants turtles have a strange-looking, non-pigmented punk spot on their head called the pineal which, new research suggest, functions like a skylight in their skull, which enables the turtles to sense subtle changes in sunlight.
Once summer comes to an end, the turtles stop foraging and leave their feeding grounds, which can be thousands of miles away from their breeding grounds, and head south. How they know when to start this journey has long puzzled researchers. In order to investigate this, team led by John Davenport from University College Cork examined a database of leatherback sightings in waters around Great Britain and Ireland.
After comparing the sightings to historical data for sea surface temperatures and day lengths to see if the levels or periodicity of either environmental triggers would prompt foraging turtles to turn south and leave their feeding grounds at summer’s end, the team found that sea surface temperatures were too variable and slow to change to be useful of a trigger. Instead, it was the shortening of day length as the late summer equilux approaches provides a credible cue to the changing seasons.
Read more about the story at Smithsonian.