Uncovering spatial learning skills of non-nomadic tortoises: Use of environmental geometry and landmark for reorientation

The Hermann tortoise (Testudo hermanni) is a non-nomadic reptile whose behavioural and cognitive phenotype is still unknown. These animals hibernate for more than 6 months/year, are sensitive to climate changes, and little prone to move substantially. However, they have sight and smell developed well, exhibit lateralised behaviours, and good homing capacities in the wild. Evidence on spatial cognition is lacking and limited to ethological observations in natural contexts. In order to start filling the gap, the present study explored the use of environmental geometry alone or in conjunction with a conspicuous landmark for spatial reorientation, in semi-controlled conditions. This study covers three years of data acquisition at the natural site “Sperimentarea” (Civic Museum Foundation of Rovereto, Trento, Italy), during which time adult male tortoises were trained within a rectangular opaque arena and required to use the distinctive geometry only (Experiment 1) or together with a conspicuous landmark (a blue wall) (Experiment 2 and 3). The arena had one door at each corner, through which the tortoise could access an outer feeder box, for being rewarded in the case of correct choices. If the tortoises used (1) the distinctive geometry, we would expect boundary mapping, i.e., choices towards the two symmetric corners with a short/long wall on the left/right; (2) the distinctive geometry in conjunction with the landmark, we would expect significantly higher choices towards one exact target location, i.e., the corner with a short/long blue wall on the left/right. Results showed that the tortoises learned to use the distinctive geometry of the arena and to integrate it with the featural cue provided by the blue wall landmark, while varying its proximity in relation to the correct corner. In doing so, they displayed a wall-following strategy of motion at the population level, whereas left/right preferential directions at the individual level. This study highlights geometric reorientation capacities in the Hermann tortoise, despite non-nomadic habits, giving validity to a novel methodological approach to test learning behaviour in these undiscovered animals, and laying the foundation for delving into exploratory patterns to build long-term spatial knowledge.