Meeting Abstract

48.7  Sunday, Jan. 5 11:30  Baby come back: Geographic shifts in sea turtle nesting provide evidence for geomagnetic imprinting BROTHERS, JR*; LOHMANN, KJ; University of North Carolina, Chapel Hill; University of North Carolina, Chapel Hill brotherj@live.unc.edu

Some migratory animals return to reproduce in the same geographic region where they began life, a behavior known as natal homing. Loggerhead sea turtles from the southeastern US provide an iconic example. These turtles circumnavigate the North Atlantic before returning, as adults, to lay eggs on the same area of coastline that they left as hatchlings. The mechanism for natal homing is unknown, but the geomagnetic imprinting hypothesis proposes that young turtles imprint on the magnetic field of their natal beach and use this information to return years later. This strategy appears plausible because the earth’s magnetic field varies spatially and most nesting beaches have unique magnetic signatures. Furthermore, loggerheads can detect the magnetic signatures that exist in different geographic regions. The geomagnetic field is not stable and the field at a given location drifts slightly over time. Along the Florida peninsula the field has moved in such a way that at some times and places magnetic signatures converge along the coast, while at others they drift farther apart. In principle, if the geomagnetic imprinting hypothesis is correct, then these changes in the field should cause detectable shifts in nesting distributions. An analysis of Florida nesting data revealed that areas of magnetic convergence are characterized by an increase in nest density, while areas of divergence are associated with a decrease. This finding is consistent with the magnetic imprinting hypothesis and implies that sea turtles use magnetic cues to target nesting beaches.