Behavioural strategies or just individual variation in behaviour? — A lack of evidence for active and passive piglets

Abstract

We criticize the recent paper by Hessing et al. (1993, Appl. Anim. Behav. Sci., 37: 285–295), where it is concluded that there are “consistent individual behavioural strategies in social and non-social situations in pigs”, resembling the active and passive coping strategies of mice. We argue: (1) The authors have not demonstrated that the underlying distributions of individuals deviate from a normal distribution. Thus the existence of two distinct types of individuals is a premise of the research and not a conclusion. It is arrived at by choosing arbitrary cut-off points. (2) The social test used is not suited for determining individual characteristics, and the so called back test is difficult to interpret. It has not been verified that the back test is a non-social test. (3) The two-way classification based on these two tests excludes a substantial proportion of the piglets. We conclude that the authors provide no evidence for distinct individual types of piglets.