Perceptual and motivational aspects of detour behaviour in young chicks

Abstract. The effects of goal visibility and distance on detour behaviour in 2-day-old chicks, Gallus gallus domesticus, were investigated. Cagemates were used as goals and placed behind barriers that concealed them to various degrees. Times needed to develop itineraries to pass round the barrier between the chick and the goal decreased with decreased visibility and increased distance of the goal. Under similar conditions of physical concealment of the goal, however, vertical-bar barriers took longer to negotiate than horizontal-bar barriers. Disocclusion of the goal mediated by the animal's movements did not seem entirely to account for this asymmetry: chicks seemed to have difficulty in considering vertical bars that concealed a goal as natural obstacles. Visual interaction between cagemates used as goals made the task easier, whereas the number of cagemates visible behind the barrier had no effect. The results suggest that most of the alleged difficulty of chicks in detour problems arises from the use of procedures that maximize confounding motivational factors and of unnatural stimuli that do not allow the animal to perceive the 'barred character' of an obstacle.