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First published online November 10, 2003

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The Journal of Experimental Biology 206, 4413-4423 (2003)
doi: 10.1242/jeb.00660

Mechanisms of homing in the fiddler crab Uca rapax 1. Spatial and temporal characteristics of a system of small-scale navigation

John E. Layne^*, W. Jon P. Barnes and Lindsey M. J. Duncan

Division of Environmental and Evolutionary Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, Scotland, UK

^* Author for correspondence at present address: Department of Entomology, Cornell University, Ithaca, NY 14853, USA (e-mail: JL272{at}cornell.edu)

Accepted 11 August 2003

Fiddler crabs Uca rapax are central-place foragers, making feeding excursions of up to 2 m from their burrows. We describe the natural feeding excursions of path-integrating fiddler crabs and analyze their paths for signs of significant systematic or random navigation errors. No signs of any systematic errors are evident. Random errors are small, probably due to a combination of the short length and low sinuosity of the foraging paths, as well as the fiddler crabs' unique method of locomotion that allows them to remain oriented to their burrows throughout the foraging path and to minimize large body turns. We further examined the extent to which their body orientation during foraging (transverse body axis pointing more or less towards home) accurately represented their stored home vector. By examining sequences of fast escape, we have shown that crabs can correct for deviations of their transverse body axis from home during their escape path. Thus their stored home vector is independent of their moment-to-moment body orientation.

Crabs were subjected to passive translational displacements and barrier obstructions. Responses to translational displacements were identical to those observed by previous authors, namely that crabs returned in the correct egocentric direction and distance as though no displacement had occurred. Covering the burrow entrance resulted in crabs returning to the correct position of the burrow, and then beginning to search. When a barrier was placed between foraging crabs and their burrow, crabs oriented their bodies toward the burrow as accurately as with no barrier.

Key words: fiddler crab, Uca rapax, path integration, homing, spatial orientation, central-place forager, systematic error

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