Cognitive Judgement Bias Test Applied to Reptiles for the First Time: Red-footed Tortoises Show Evidence of Long-Term Mood States

Reptiles have long been shown to exhibit responses such as anxiety, stress, and preference when handled, exposed to novel environments, or choosing preferred foods. However, compared with mammals and birds, research on reptile emotions remains limited. As a result, whether reptiles possess emotional capacities similar to those of other vertebrates remains an important question in animal behaviour research.

Researchers often use cognitive judgement bias tests to assess animals' emotional states. This method has been widely applied in mammals and birds by observing how animals interpret ambiguous information, allowing researchers to infer whether they respond more optimistically or pessimistically, and whether they possess longer-lasting mood states. However, this approach has rarely been applied to reptiles.

A 2025 study was the first to apply cognitive judgement bias testing to reptiles, investigating whether they also possess mood states that persist over time, and whether short-term emotions such as anxiety are associated with longer-term mood.

The study used 15 red-footed tortoises (Chelonoidis carbonaria) of different ages. Individuals were assigned to different-sized test arenas according to their body size to avoid body size influencing the results.

Experimental setup（Image source：Hoehfurtner, T et al. (2025).， CC BY 4.0 。）

The researchers first assessed each tortoise's emotional state using a cognitive judgement bias test. Before testing, the tortoises were allowed to become familiar with the testing arena. They were then trained to distinguish between two fixed locations, where one food bowl always contained food while the other never did. After the tortoises learned the difference, the bowl was placed at several intermediate locations between the two, allowing the researchers to observe how the animals responded to uncertain situations.

If a tortoise approached these locations more quickly, it was considered more likely to expect food to be present, which the researchers interpreted as an optimistic judgement. In contrast, if it hesitated for longer before approaching, it was considered more likely to expect no food, which was interpreted as a pessimistic judgement. In this way, the researchers aimed to determine whether tortoises possess mood states that persist over time.

After completing the cognitive judgement bias test, the researchers conducted two behavioural tests commonly used to assess anxiety in reptiles to observe how the tortoises responded to novel stimuli.

The first was the Novel Object Test, in which an object the tortoises had never seen before was placed into the familiar testing arena. The researchers recorded how long it took each tortoise to begin moving, how long it took to approach the object, and the degree of head extension. Previous studies have shown that red-footed tortoises tend to extend their heads further when they are more relaxed or confident, making head extension a useful indicator of emotional state.

The second was the Novel Environment Test, in which the tortoises were placed into a modified arena with changes to features such as the colours, textures, and patterns of the walls and floor to increase environmental novelty. The researchers again recorded the time taken to begin moving and the degree of head extension.

Finally, the researchers compared each tortoise's performance in the cognitive judgement bias test with its performance in the two anxiety tests to determine whether optimistic or pessimistic judgement tendencies were associated with behavioural responses to novel objects and novel environments.

The red-footed tortoise is thought to possess a certain degree of emotional capacity.（Image source：Flints， CC BY-SA 3.0 。）

The results showed that red-footed tortoises performed in the cognitive judgement bias test much like mammals and birds in previous studies. The closer the food bowl was placed to the rewarded location, the faster the tortoises approached it, suggesting that they used previous experience to make different judgements about ambiguous situations. Overall, the tortoises tended to judge ambiguous locations as more likely to contain food, indicating an optimistic judgement bias.

These findings suggest that reptiles may possess a broader range of emotional capacities than previously believed. They may not only experience short-term emotional responses, such as stress or pleasure, but also longer-lasting mood states. However, because the study only examined red-footed tortoises, further research is needed to determine whether other reptile species show similar abilities.

The researchers also compared the results of the cognitive judgement bias test with the two anxiety tests. Individuals showing more optimistic judgements generally displayed less anxiety when exposed to a novel environment, such as extending their heads further. In contrast, individuals showing more pessimistic judgements took longer to approach a novel object, suggesting higher levels of anxiety.

These differences were not simply due to some individuals moving faster than others, but were related to how they interpreted ambiguous situations. This suggests that the cognitive judgement bias test reflects emotional state rather than general activity level.

However, the researchers found no significant correlation between the two anxiety tests. They suggested that although both novel objects and novel environments represent novel stimuli, they may evoke different types of emotional responses and therefore do not necessarily produce the same behavioural patterns.

Overall, the findings suggest that reptiles may possess richer emotional capacities than previously believed, and the study is also the first to demonstrate that cognitive judgement bias testing can be applied to reptiles, providing a new tool for assessing their emotional states.

If reptiles are capable of experiencing not only short-term emotions but also longer-lasting mood states, together with the growing evidence that they possess higher cognitive abilities than previously recognised, captive management practices may also need to change. For example, providing more complex and cognitively challenging environments may not only reduce negative emotional states but also promote positive emotional experiences, thereby improving the welfare of captive reptiles.

（Author: Bai Leng）

Reference：

Hoehfurtner, T., Wilkinson, A., Moszuti, S. A., Burman, O. H. P. (2025). Evidence of mood states in reptiles. Animal Cognition.