Do Hermann's tortoises (Testudo hermanni) discriminate colours? An experiment with natural and artificial stimuli

Many animals use chemical and visual cues to obtain reliable information about potential food resources. Most reptiles have evolved highly specialized chemosensory and visual capacities, in particular colour vision, to accomplish this task. By presenting animals with flowers and coloured cardboard discs in two-choice experiments, we examined whether both male and female Hermann's tortoises (Testudo hermanni) were able to distinguish between different colours, and show some preference for certain colours. We found that both sexes responded and discriminated equally between different colours, with some differences between flowers and discs. In particular, the red was preferred in the disc experiment, mainly by males, but was disregarded by both sexes in the flower experiment, where red was represented by poppy, Papaver rhoeas. This suggests that Hermann's tortoise probably relies on a mixed system of olfactory and visual abilities to detect food in order to optimize the intake of essential nutrients as minerals or carotenoids. Our results demonstrate that the most preferred colour by tortoises was the yellow, which might reflect carotenoid content, and we discuss the potential implications of this finding.