Stereotyping starlings are more ‘ pessimistic ’ 1 2 3

26 Negative affect in humans and animals is known to cause individuals to interpret 27 ambiguous stimuli pessimistically, a phenomenon termed ‘cognitive bias’. Here, 28 we used captive European starlings (Sturnus vulgaris) to test the hypothesis that 29 a reduction in environmental conditions, from enriched to non-enriched cages, 30 would engender negative affect, and hence ‘pessimistic’ biases. We also explored 31 whether individual differences in stereotypic behaviour (repetitive somersaulting) 32 predicted ‘pessimism’. Eight birds were trained on a novel conditional 33 discrimination task with differential rewards, in which background shade (light or 34 dark) determined which of two covered dishes contained a food reward. The 35 reward was small when the background was light, but large when the background 36 was dark. We then presented background shades intermediate between those 37 trained to assess the birds’ bias to choose the dish associated with the smaller 38 food reward (a ‘pessimistic’ judgement) when the discriminative stimulus was 39 ambiguous. Contrary to predictions, changes in the level of cage enrichment had 40 no effect on ‘pessimism’. However, changes in the latency to choose and 41 probability of expressing a choice suggested that birds learnt rapidly that trials 42 with ambiguous stimuli were unreinforced. Individual differences in performance 43 of stereotypies did predict ‘pessimism’. Specifically, birds that somersaulted were 44 more likely to choose the dish associated with the smaller food reward in the 45 presence of the most ambiguous discriminative stimulus. We propose that 46 somersaulting is part of a wider suite of behavioural traits indicative of a stress 47 response to captive conditions that is symptomatic of a negative affective state. 48 49 50 51