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...