A proposal for assessing individual differences in behaviour during early development in the domestic cat

Despite growing interest among biologists in animal personality, including in applied contexts, there have been few developmental studies of how and when differences in animal personality arise. And yet, efficient detection of personality differences early in development could be useful in selecting individuals for various management purposes. In a first step towards addressing this, we report results of a study of individual differences in general motor activity among littermates of the domestic cat, obtained using an observational method designed to overcome the difficulties of evaluating the behaviour of newborn altricial young. Three litters (14 kittens) were filmed in the absence of the mother at regular intervals across the 1st postnatal (pre-weaning) month. Six untrained observers independently viewed 10 videos for each litter and ranked the kittens in each video from the least to the most active. Significant differences were found between at least some kittens in all three litters (Friedman tests: Fr = 16.3, 25.8, 11.3; P < 0.0001, 0.0001, 0.0085, respectively), and there was significant agreement on kitten ranks among the six observers (Kendall coefficients of concordance: W = 0.84, 0.84, 0.55; P < 0.01 for the three litters, respectively). There was also significant agreement between the results of two observers using the ranking method and a quantitative method of behavioural assessment (Spearman rank order correlation: rs = 0.93, P = 0.001). We conclude that stable individual differences in general motor activity, possibly indicating differences in temperament, are present in kittens early in development, and that ranking the degree of such behaviour in a naturalistic setting provides a valid and efficient method of detecting such differences. It is now necessary to investigate if such early differences are predictive of later behavioural phenotypes.