|Cheng, Heng Wei|
Submitted to: Journal of Animal Behavior
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2003
Publication Date: N/A
Citation: Interpretive Summary: Broiler chickens in large groups do not space themselves evenly but instead crowd in particular areas, which may increase mortality and exacerbate welfare problems arising from social stress. One contributing factor may be a deficit in spatial skills arising from the absence of essential environmental factors during routine rearing. Experiments were conducted to examine the development of spatial skills. It was found that providing screens for 4 days so that chickens could leave sight of each other increased movement when released into a large pen, and improved memory for the location of out-of-view objects, compared to chickens provided with no screens. It is proposed that rearing in complex environments and providing visual cover could ameliorate the welfare problems in large flocks associated with crowding.
Technical Abstract: At around day 11 of life, domestic chicks show a tendency to move out of sight of their mother before returning and regaining social and visual contact. A series of experiments was conducted to investigate the role of this voluntary "out-of-sight" behaviour on the development of spatial memory in young chicks. Performance on various spatial tests was compared between chicks reared in environments providing the opportunity to move out-of-sight of an imprinting object (occlusion-experienced chicks) and occlusion-naive chicks. As in natural conditions, a peak in out-of-sight behaviour was found on day 11 compared with days 10 or 12 (ANOVA: F2,20=20.2, P<0.001). Occlusion-experienced chicks walked more than occlusion-naive chicks when released into a large novel arena (ANOVA: F1,14=11.9, P<0.01), but otherwise showed similar degrees of dispersal. Occlusion-experienced chicks tended to show better retrieval of a visually displaced imprinting stimulus than occlusion-naive chicks (Chi-squared test: ?23=6.3, P=0.09). Occlusion-experienced chicks tended to make fewer orientation errors in the first (Kruskal-Wallis test: H3=7.0, P=0.07) and subsequent trials (Kruskal-Wallis test: H3=7.6, P=0.05) of a detour test. Chicks making at least one orientation error had spent less time out-of-sight of the imprinting stimulus on day 11 than chicks making no orientation errors (ANOVA: F1,18= 6.5, P<0.05). In contrast, experimentally manipulating the amount of time that chicks were out-of-sight of an imprinting stimulus (by confining the chicks) had no effect on performance in displacement or detour tests. Results suggest that egocentric orientation in chicks is improved by allowing them to express out-of-sight behaviour in early life. It is concluded that rearing in complex environments and providing visual cover could ameliorate the welfare problems in large flocks associated with crowding.