Graduation Year

1996

Document Type

Thesis

Degree

M.S.

Degree Name

Master of Science (M.S.)

Department

Biology

Degree Granting Department

Biology

Major Professor

Henry R. Mushinsky, Ph.D.

Co-Major Professor

Earl D. McCoy, Ph.D.

Committee Member

Philip J. Motta, Ph.D.

Abstract

Gopher tortoises are found in xeric habitats in the southeastern United States. In these xeric habitats, gopher tortoises excavate and reside in burrows which provide shelter and protection. Gopher tortoises are active throughout the year, often making several journeys a day away from their burrows. Although they may move substantial distances, they return to their burrows, suggesting that they posses a well-developed orientation and homing ability. This study investigated the ability of gopher tortoises to home from short distance (40 meters, just outside of or on the perimeter of their home ranges) and intermediate distances (200 meters, approximately 2 home range units) away from their burrows. This study also evaluated the roles of vision and olfaction in orientation by releasing tortoises with their vision blocked and/or nares plugged. Gopher tortoises were found to be able to home from short distances away from their burrows. The mean angle they traveled was 4 degrees (0 degrees was the direction of the home burrow). The goal of the horning appeared to be the home range, not the specific home burrow. Only 1 of 15 tortoises returned to its home burrow, while 11 tortoises returned to their home range. The tortoises appeared to be well oriented as indicated by the low mean index of straightness of 1.62. Gopher tortoises also were found to be able to home from intermediate distance away from their burrows. The mean angle traveled was 358 degrees (0 degrees was the direction ofthe home burrow). Again, the goal ofthe homing appeared to be the home range, not the specific home burrow. Vision and olfaction appear to be important senses for the orientation and movements of gopher tortoises. With the senses blocked, distances moved decreased significantly and no tortoises were able to home. The mean angle moved for tortoises with their vision blocked was 145 degrees, with their nares plugged was 301 degrees, and with both blocked and nares plugged was 81 degrees (0 degrees was the direction of the home burrow). This study indicates that vision may be more important than olfaction for homing and orientation.

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