Use of multiple regression models in the study of sandhopper orientation under natural conditions

In sandhoppers (Amphipoda; Talitridae), typical dwellers of the supralittoral zone of sandy beaches, orientation with respect to the sun and landscape vision is adapted to the local direction of the shoreline. Variation of this behavioural adaptation can be related to the characteristics of the beach. Measures of orientation with respect to the shoreline direction can thus be made as a tool to assess beach stability versus changeability, once the sources of variation are correctly interpreted. Orientation of animals can be studied by statistical analysis of directions taken after release in nature. In this paper some new tools for exploring directional data are reviewed, with special emphasis on non-parametric smoothers and regression models. Results from a large study concerning one species of sandhoppers, Talitrus saltator (Montagu), from an exposed sandy beach in northeastern Tunisia are presented. Seasonal differences in orientation behaviour were shown with a higher scatter in autumn with respect to spring. The higher scatter shown in autumn depended both on intrinsic (sex) and external (climatic conditions and landscape visibility) factors and was related to the tendency of this species to migrate towards the dune anticipating winter conditions.