Homing behavior, navigation, and orientation of juvenile sea turtles

by Avens, Larisa I.

Larisa I. Avens Homing behavior, navigation, and orientation of juvenile sea turtles. (Under the direction of Kenneth J. Lohmann) The present study was conducted to investigate homing behavior in juvenile sea turtles and to determine the mechanisms used by the turtles to navigate and orient. Homing behavior of juvenile loggerhead turtles captured in inshore waters was studied through a combination of mark-recapture techniques and radio telemetry. Turtles were tagged, displaced moderate distances, and released. Juvenile loggerheads were often recaptured both within a given year, as well as during subsequent years, and many displaced turtles returned rapidly to the capture area. In addition, juvenile loggerhead and green turtles were displaced from capture sites and tested in an experimental arena to determine whether (1) the turtles exhibit homing behavior and migratory orientation in a controlled setting and (2) homing was accomplished using true navigation. Loggerhead and green turtles captured to the northeast of the testing site during the summer oriented in a direction that corresponded with the most direct path back to the capture area, as did loggerheads captured southwest of the testing site at the same time of year. Both loggerheads and green turtles tested during the fall oriented southward, which is a direction consistent with the migratory orientation observed in wild turtles at that time of year. These results indicate that the orientation behavior of loggerhead and green turtles in the arena setting accurately ii reflects that of wild turtles and suggest that loggerheads are capable of map-based navigation. Preferred orientation in the arena setting made it possible to begin investigation of the cues used by juvenile loggerheads to orient. Turtles established and maintained headings in specific directions in the absence of wave cues, familiar landmarks, and chemical gradients. Juvenile loggerheads were also able to maintain a consistent directional heading when either the magnetic field surrounding the anterior portion of the body was distorted using powerful magnets or when the turtles were outfitted with frosted goggles, which blocked visual cues. However, when the turtles experienced a simultaneous disruption of magnetic and visual cues their orientation was altered. These results demonstrate that juvenile loggerheads can use either magnetic or visual cues to orient, depending on which is available. iii To my husband Chris, for his patience, understanding, assistance, and advice iv