In both humans and animals, a negative emotional state (referred to as ‘negative affect’) tends to make individuals interpret any ambiguous stimulus in a more pessimistic way – for example, a neutral facial expression might be interpreted as sad or angry. This phenomenon is called a 'cognitive bias'. A negative cognitive bias might be inherent to particular individuals (such as those suffering with depression) or might be induced in individuals by altering the conditions in which they live. The relationship between housing conditions and affective state is important for animal welfare but has been little investigated. In this study conducted by Dr. Melissa Bateson and Dr. Ben Brilot, with Dr. Lucy Asher from the Royal Veterinary College, captive European starlings were tested to see whether a reduction in the quality of environmental conditions, from enriched cages (those with natural branches, a water bath and a tray of bark chippings) to non-enriched cages, would lead to a negative affect, and hence induce a more 'pessimistic' cognitive bias. They also explored whether there was any relationship between displays of repetitive behaviour (somersaulting) and pessimism. To do this birds were trained on a choice task in which the background shade (light or dark) determined which of two covered dishes contained a food reward. The reward was small (one mealworm, the birds favourite treat) when the background was light, but large (three mealworms) when the background was dark. What the group wanted to know was how would the birds interpret ambiguous background shades that were intermediate between those used in training – would they be ‘pessimistic’ and assume it meant a smaller food reward or ‘optimistic’ and assume the larger reward. The group found that changing the level of cage enrichment had no effect on which outcome the birds assumed. However, they did observe individual differences that related to whether or not the birds had previously displayed repetitive (stereotyped) behaviour. Specifically, in the presence of the most ambiguous stimulus the birds that displayed somersaults were more likely to be pessimistic and choose the dish associated with the smaller food reward. From these results the group have proposed that somersaulting is one of number of behaviours that may be symptomatic of a negative affective state. Being able to predict how an animal is feeling from the display of particular behaviours is an important way of being able to judge how captive animals react to their environment and to design ways to improve housing conditions.
Stereotyping starlings are more 'pessimistic'. Brilot BO, Asher L, Bateson M (2010) Animal Cognition 13: 721-731 (PubMed abstract: http://www.ncbi.nlm.nih.gov/pubmed/20464439)
published on: 1st September 2010