No evidence of body size awareness in the Hermann's tortoise (Testudo hermanni)

Navigating structurally complex environments often requires assessing whether an opening affords safe passage, a task that presupposes relying on an internal representation of body size. Evidence for such awareness has been reported in mammals and birds and may also occur in other vertebrates and invertebrates. We investigated this ability in the tortoise Testudo hermanni, a species that often encounters dense vegetation and narrow passages. We first assessed the tortoises' ability to distinguish between 2 apertures of different widths. Surprisingly, they discriminated only when one aperture was twice as wide as the other, a performance markedly lower than that reported in other species. We then examined whether tortoises chose an aperture based solely on its suitability for their body size rather than by comparing the 2 apertures. However, tortoises chose the narrower opening at similar rates regardless of whether it was passable and persisted in attempting passage even when it was inadequate. When examined in a different context, food quantity discrimination, tortoises exhibited the same lack of selectivity. Overall, our findings suggest that T. hermanni does not rely on body size when negotiating obstacles, possibly reflecting poor visual discrimination capacities or the evolution of alternative strategies for overcoming physical barriers.