Orientation of Sandhoppers Under Natural Conditions in Repeated Trials: an Analysis Using Longitudinal Directional Data

Sandhopper orientation under natural conditions: Comparing individual tracks

“…The track analysis of the present study is in agreement with that result: the tracks of the laboratory-born individuals, having no experience of the beach, were more scattered and less properly directed seawards than those of the wild individuals. Borgioli et al (1999a, b);D'Elia et al (2001) analyzed sandhopper orientation through subsequent releases of the same individuals (longitudinal circular data, Song, 2007) and observed an improvement of orientation from the first to the fifth release. The study of longer tracks (from the emergence to a new burrowing into the sand) may yield more information on the behavior of sandhoppers, being less stressful for the animals than repeated releases.…”

“…Theoretically, when individuals are displaced in the upper beach, they orient to the theoretical escape direction seawards (TED) following a trajectory nearly perpendicular to the shoreline (Pardi and Papi, 1953). The sun compass was shown to be genetically fixed in those populations where the shoreline had not changed in the long term (centuries), while on highly dynamic, eroded or accreting shorelines (changing in the medium term of years or decades) sandhoppers tend to scatter in various directions, or to orient on the basis of local landscape features Borgioli et al, 1999b;D'Elia et al, 2001). Scattering can depend on genetic variation or behavioral flexibility.…”

“…The orientation capabilities of this population and innateness of the sun compass were known from previous studies carried out both on the beach and far from it, offering a sound background to the study of the tracks (Scapini, 1979;Ugolini and Scapini, 1988;Borgioli et al, 1999a, b;Scapini et al, 1999;D'Elia et al, 2001;Ugolini et al, 2009;Fanini et al, 2009;Ugolini et al, 2012a, b). San Rossore beach is located at a distance of about three km from the Arno River mouth and has been subject to strong erosion from the sea, necessitating mitigation measures to contrast the loss of sediment, such as filling it in with material of land origin (wood and gravel), groyne building and beach nourishment (Aminti, 1997;Cipriani et al, 2001;Fanini et al, 2007).…”

“…Other orientation cues were also shown to be used by talitrids under natural conditions, e.g., beach slope (Ercolini and Scapini, 1974). The possible effect of wind direction on sandhopper orientation was excluded in previous experiments by using screened arenas, or was considered a disturbing factor (Borgioli et al, 1999a;D'Elia et al, 2001;. However, the regularity of winds on beaches with respect to the land-sea axis make wind a good candidate cue in addition to the more studied visual orientation cues.…”

Circular data

“…Projected normal regression is used to study the orientation of sandhoppers in Ref 67. Circular regression is applied to the same problem in Ref 68. Circular time series methods are applied to the tracks of bark beetles in Ref 69.…”