Effects of social and environmental familiarity on group preferences and spacing behaviour in laying hens

Abstract

Litter-kept hens were tested using a ‘free-choice’ situation, to investigate the effects of social and environmental familiarity on their spacing behaviour. In Experiment 1, social familiarity affected spacing, with subject birds which were familiar with each other spreading evenly over the available area as evidenced by a significantly lower ‘Spread of Participation Index’ (mean SPI 0.301–0.406), whereas less familiar birds clumped (mean SPI 0.453–0.646; P < 0.01) and fought more frequently. There were no clear effects of environmental familiarity. In a second experiment we used a T-maze to investigate effects of social familiarity on group preferences and behaviour in the chosen groups. There was no significant preference for familiar, semi-familiar or unfamiliar groups of companion hens. However, the incidence of aggressive pecks was significantly higher in small semi-familiar (mean 1.1 ± 0.6 pecks per hen per 5 min) and unfamiliar (mean 1.8 ± 0.5 pecks per hen per 5 min) than in large semi-familiar (mean 0.1 ± 0.1 pecks per hen per 5 min) and unfamiliar groups (0.1 ± 0.1 pecks per hen per 5 min; P < 0.001). Threats were more common in small familiar groups (0.2 ± 0.1 threats per hen per 5 min) than in small semi-familiar groups (0.1 ± 0.1 threats per hen per 5 min; P < 0.05) and were absent in the remaining group options. Relative social dominance of the subject hens had no effect on choices or on behaviour and there was no significant correlation with their behaviour in the companion hen groups. The results suggested that hens were unable to distinguish the relative familiarity level of companion hens from the T-maze or, alternatively, that making such a distinction was unnecessarily costly to the subject hens.