Relationship between agonistic behaviour, physical condition and movement patterns of laying hens in aviaries

Laying hens show inter-individual variation in fighting ability in agonistic interactions. However, in large groups exceeding 100 animals, the impact of this variation remains largely unexplored. In such environments, hens which frequently submit to others, may experience restricted access to resources, potentially leading to compromised health and welfare. Conversely, they may adapt by altering movement patterns to avoid interactions with dominant hens. We investigated how fighting ability relates to the physical condition and movement of hens in large groups in a quasi-commercial aviary system. We observed 36 focal birds (Dekalb White) across six pens, each housing 225 hens. Focal birds were selected from 18 birds per pen based on comb sizes to capture extremes in fighting ability. Social behaviour was observed for two hours per hen at 23, 25, and 27 weeks of age (WoA), and fighting ability was quantified as winning ratio (wins relative to the total of agonistic encounters). Additionally, every 4–7 weeks we assessed the animals’ body weight, keel-bone fracture (KBF) severity, plumage condition and aggressive pecking damage (i.e., comb injuries combined with head and neck plumage condition). A tracking system recorded the movements between the aviary tiers from 22 to 55 WoA (164 days), from which we extracted daily spatial and movement variables. Mixed effects models, incorporating WoA and winning ratio and their interaction as independent variables, were employed for analysis. Results indicated that birds with higher winning ratios were heavier over time than those with a lower ratio, whereas no effect of winning ratio was detected on KBF severity, plumage condition or aggressive pecking damage. Analysis of daily spatial and movement variables revealed that hens with higher winning ratios progressively spent less time on the highest tier. Before 30 WoA, they also travelled greater distances between tiers, suggesting increased space use, particularly in the period shortly after barn population than birds with lower winning rations. These findings suggest that fighting ability may relate to body weight and space-use strategies in large groups, although the mechanisms remain unclear. The observed differences in weight and space-use could reflect restricted access to feed and preferred areas for hens with lower winning ratios, or their active avoidance of agonistic encounters. Alternatively, they may stem from inherent behavioural differences between individuals. Future studies should aim to disentangle potential mechanisms by investigating individual resource access and decision-making in large-group housing systems, to clarify how fighting ability affects long-term welfare in commercial aviary systems. • Social behaviour, body condition, and movement of hens were observed in an aviary. • Fighting ability in agonistic interactions was quantified as winning ratio. • Hens with high winning ratios were heavier over time than hens with low ratios. • Winning ratio was not related to fractures, plumage condition, or pecking damage. • Hens with high winning ratios transitioned more and were less on the highest tier.