Zajonc R B, Wilson W R, Rajecki D W
Anim Behav. 1975 Feb;23(1):131-8. doi: 10.1016/0003-3472(75)90059-7.
Discrimination between individual strangers and companions was examined in day-old domestic chicks. In one experiment, pecking rates at companions and strangers were observed in pairwise bouts after 16 hr of cohabitation. The discriminability of strangers and companions was varied by means of pre-hatch colouring. Reliable discriminations between individual strangers and companions emerged as early as the first minute of the encounter. Discriminative cues provided by artificial colouring were found not to be necessary in establishing social discrimination. In a second experiment, undyed chicks were housed in pairs for 1, 4 or 16 hr. Half of the pairs lived in cages that separated companions by a wire screen, and half were housed in undivided cages. Observations of pecking in four-way bouts confirmed previous findings and demonstrated that the opportunity to peck during exposure may be a necessary condition in producing social discrimination. Antecedent conditions that lead to the development of affiliative bonds simultaneously appear to establish social discrimination.
