Hatchling sea turtles emerge from underground nests on oceanic beaches, crawl to the sea, and swim directly offshore to the open ocean. At no point in the life cycle are orientation abilities more vividly displayed, or more crucial to survival. Hatchlings are small and defenseless, and they move too slowly to evade predators. Minimizing time on the beach thus reduces the likelihood of being eaten by animals such as racoons, foxes, and ghost crabs. Similarly, moving rapidly through shallow, near-shore waters to the open sea reduces exposure to predatory fish and birds that are concentrated in coastal areas. It is therefore not surprising that natural selection has favored orientation mechanisms that guide young turtles quickly and reliably to the relative safety of the open ocean along paths that approximate straight lines.

 

A hatchling loggerhead turtle emerges from its egg shell.	More than 100 hatchlings may emerge from a single nest.

      The orientation mechanisms of hatchling sea turtles have been studied most thoroughly along the east coast of Florida, U.S.A. In this geographic region, baby loggerhead turtles swim offshore to the Gulf Stream, a vast, warm-water current that sweeps north along the Florida coast. Along the way, turtles appear to use three different sets of orientation cues. The set of web pages that comprise the offshore migration module summarize how hatchlings use visual cues, wave direction, and the Earth's magnetic field to stay on course and guide themselves from their nests to the Gulf Stream during their first few days of life.

References:

Lohmann, K. J., and C. M. F. Lohmann. 2003. Orientation mechanisms of hatchling loggerheads. In: Loggerhead Sea Turtles (eds. A. B. Bolten and B. E. Witherington), pp. 44-62. Smithsonian Books: Washington.

Lohmann, K. J., Witherington, B. E., Lohmann, C. M. F., and M. Salmon. 1997. Orientation, navigation, and natal beach homing in sea turtles. In: The Biology of Sea Turtles (eds. P. Lutz and J. Musick), pp. 107-135. CRC Press: Boca Raton.

Lohmann, K. J., and C. M. F. Lohmann. 1996. Orientation and open-sea navigation in sea turtles. Journal of Experimental Biology. 199: 73-81. [Download pdf]