Effect of experience of occlusion events on the domestic chick's strategy for locating a concealed imprinting object

Abstract

We investigated how positional and directional cues affected the way single domestic chicks, Gallus gallus domesticus, searched for a concealed imprinting object. The chicks were 4 or 12 days of age and had been reared in enriched pens that allowed them to move out of sight of the imprinting object, or control pens that did not. In experiment 1, 44 chicks viewed a positional cue, which was a stationary imprinting object placed for 1min in front of one of two possible hiding locations (each concealing an identical imprinting object) either to the left or right of the chick. When released, chicks moved towards, and spent more time in, the side in which the positional cue had been presented. We presented a further 44 chicks with a directional cue, which involved an imprinting object moving from near one possible hiding location towards the other and its occlusion midway between the two possible hiding locations. When released, chicks moved towards, and spent more time in, the opposite side to that indicated by the visible direction of movement of the imprinting object. Additionally, chicks reared in enriched pens spent more time in the side in which the imprinting object was seen than chicks reared in control pens. We examined the relative influence of positional and directional cues in experiment 2, by providing both cues sequentially to 88 chicks. Chicks spent more time in the positional cue side, when the directional cue offered complementary information, but no side preference was found when cues provided contradictory information. We conclude that in this study, orientation towards a concealed object was based on previous spatial location alone, with little influence from the temporal aspects of the presentation such as movement before occlusion or last-seen location. We discuss the possibility that chicks imprinting on a stationary object develop a strategy for locating a concealed social stimulus that is unrepresentative of chicks reared by a hen.