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Although there are many reports of animals using visual landmarks to relocate their homes, little is known about animals who construct visual orientation landmarks for homing. Crabs living on intertidal mudflats cannot see their burrow openings when they are more than 7-8 eye heights away. They are known to use a path integration method for short-range homing by calculating travel distance using leg odometry and aligning their transverse body axis to their home vector. However, active courtship or territorial behavior may introduce errors into their estimate of home direction and this could increase predation risk. Males may also use the courtship structures for visual landmark orientation to compensate for errors in path integration while courting females. I explored this hypothesis in the fiddler crab Uca lactea. Dislocated males could orient to their burrows from a greater distance when a semidome was placed at the burrow entrance than when it was absent. In addition, when a semidome was translocated, courting males moved toward the semidome more frequently than non-courting males did. Finally, males with semidomes moved more freely during courtship (by tolerating larger deviations of the transverse body axis from the home vector) than males without semidomes. These results support the hypothesis that the courtship structures of this species function not only to attract females but also to provide a visual landmark for reliable and efficient homing. |