Laying hens performing gregarious nesting show less pacing behaviour during the pre-laying period

The phenomenon of gregarious nesting occurs when hens choose to enter and lay their eggs in a nest box which is already occupied by one or more hens, even when an empty nest box is also available. It has been suggested that inexperienced hens copy the nest selection preferences of experienced hens until their own preferences have developed. In addition, gregarious nesting has been found to be an anti-predator behaviour, indicating that fear may be a factor inducing gregarious nesting. Individual differences in sociality and dominance hierarchy may also be important factors. The aim of the current study was to investigate the relationship between the individual level of fearfulness, sociality and hierarchical dominance, and the performance of gregarious nesting behaviour in laying hens. Fifteen-week-old laying hens (Isa Warren, n = 180) were housed in groups of 15 individuals. At 20-21 weeks of age, nesting behaviour and agonistic interactions were recorded. Furthermore, behavioural tests reflecting fearfulness (tonic immobility and novel object tests) and sociality (social reinstatement test) were performed. Based on their choices of nest boxes (occupied v. unoccupied), the hens were classified as gregarious, solitary or intermediary nesters. A dominance hierarchy was formed based on the data on agonistic interactions. The results showed that intermediary nesters, i.e. those who visited both occupied and unoccupied nest boxes roughly equally often, performed significantly more pre-laying pacing behaviour compared to gregarious nesters (P = 0.028). There was no effect of categorisation of nesting behaviour (gregarious, solitary or intermediary nesters) on body weight, responses to tonic immobility test, novel object test, social reinstatement test or dominance hierarchy (P > 0.06). The results may suggest that intermediary nesters experience more frustration compared to hens that are predominantly gregarious nesters as indicated by the increased pre-laying pacing behaviour. Alternatively, the increased pre-laying pacing behaviour could be a reflection of a longer decision-making process in unexperienced hens. In light of these different possible explanations, the cause-and-effect relationship between frustration/stress and nesting behaviour remains to be assessed.