Orientation in the European common frog Rana temporaria during the first wintering migration.

Abstract

The orientation of naive animals during their first migration is extensively studied in birds and sea turtles, whereas the data for other groups such as amphibians are still scarce. To date, it is unknown whether young-of-the-year anurans perform a random or directional search for the hibernation sites, and what cues (global or local) they use. We conducted a series of field experiments to study the orientation behavior of juvenile common frogs during their first wintering migration. We captured 1614 froglets from two subpopulations with different directions of migration and assessed their orientation in large circular outdoor arenas (20 m in diameter) on the opposite sides of the river. Before the migration, froglets used local cues and moved back towards the forest (summer habitat). At the start of migration, the froglets did not move randomly: they navigated towards the river using local cues. Later, however, before approaching the hibernation site, they memorized the compass direction of migration and followed it using global cues. Orientation along a memorized compass heading begins to dominate in the hierarchy of orientation mechanisms, and this predominance is maintained even after reaching the hibernation site. Unlike in birds, no innate direction of migration was found.