Migratory restlessness in shorebirds (Aves, Charadriiformes). A case study by means of accelerometers

The knowledge of individual and environmental parameters affecting stopover length in shorebirds is important for the conservation and management of species and habitats often seriously threatened, such as Mediterranean wetlands. The role of external factors affecting the decision to leave a stopover site is not always easy to study in the field, due to the high number of variables (i.e., atmospheric conditions) potentially involved. Combining both field and laboratory research has proved to be extremely useful in order to identify the main factors affecting stopover length, at least in passerines. Recent studies demonstrated that the amount of migratory restlessness in these species can be considered a good proxy for quantifying the willingness to depart from a refuelling site. Even if shorebirds have proved to be good models for laboratory research, the only papers regarding migratory restlessness in this group concern studies on orientation mechanisms, which are mainly aimed at showing their use of magnetic compass. The present work aims at studying the migratory restlessness in shorebirds and its relation with body conditions and stopover length by using spring migrating Wood sandpiper (Tringa glareola) as a model species. Despite this method proved to be effective in recording Wood sandpipers activity, we failed to found any relationship among their stopover length, body conditions and nocturnal activity. The degree of nocturnal activity was overall low, whereas a peak in activity was registered at sunset. This twilight activity was oriented, and its amount varied significantly according to the amount of available food in captivity. Our results suggested that migratory restlessness in shorebirds might show some peculiar characteristics that would deserve further investigations.