At the beginning of their offshore migration, hatchling sea turtles enter the ocean
at night and establish a course away from land by swimming directly into oceanic waves.
How turtles can detect wave direction while swimming under water in darkness, however,
has not been explained. Objects in a water column beneath the surface of the ocean
describe a circular movement as waves pass above. In principle, swimming turtles might,
therefore, detect wave direction by monitoring the sequence of accelerations they
experience under water. To determine whether loggerhead (Caretta caretta L.) and green
turtle (Chelonia mydas L.) hatchlings can detect wave direction in this way, we constructed
a wave motion simulator to reproduce in air the circular movements that occur beneath
small ocean waves. Hatchlings suspended in air and subjected to movements that simulated
waves approaching from their right sides attempted to turn right, whereas movements
that simulated waves from the left elicited left-turning behavior. Movements simulating
waves from directly in front of the turtles elicited little turning in either direction.
The results demonstrate that hatchling sea turtles can determine the propagation direction
of ocean waves by monitoring the circular movements that occur as waves pass above.
Although sea turtles are the first animals shown to be capable of detecting wave direction
in this way, such an orientation mechanism may be widespread among other transoceanic
migrants such as fish and cetaceans.