Toutouwai display positive judgement bias when tested in the wild

Cognition, how individuals perceive, store, process and respond to information, influences decision-making. However, biases in cognitive processes can distort behavioural outcomes. Judgement bias occurs when individuals infer information to be more positive, or negative than it is. For captive animals, judgement bias is typically measured by testing behavioural responses to ambiguous cues that are intermediate to cues with learned valence (positive and negative). However, these tests have rarely been used in the wild. We therefore examined if a behavioural test of judgement bias commonly used in captive animals could be adapted to test a wild bird, the toutouwai (North Island robin, Petroica longipes). Toutouwai were faster to approach ambiguous cues that were more similar to a learned positive cue, compared to a learned negative cue. This positive bias mirrors behavioural response patterns observed across a range of species in captivity, including other birds. Responses toward ambiguous cues were repeatable over a short timespan, indicating there was consistent individual variation among our test birds in their degree of bias when judging ambiguous cues. Males tended to approach cues more quickly than females. Our results demonstrate that judgement bias can be tested for in situ in wild birds. However, as is typical of many island species, toutouwai are bold and fearless, which facilitated their participation in our experiment. Therefore, to enable research examining the ecological correlates of judgement biases in nature, we must develop tests of cognitive biases that can be used with a wider range of species in the wild.