Keeling, L. J., Newberry, R. C., Estevez, I. 2017. Flock size during rearing affects pullet behavioural synchrony and spatial clustering. Applied Animal Behaviour Science 194, 36-41.

Animals are often synchronised in their behaviour, with costs and benefits varying according to group size and the behaviour being performed. Making decisions about optimal allocation and distribution of resources to animals in our care therefore poses theoretical and practical challenges. We investigated group size effects on behavioural synchrony and spatial clustering during daytime in pullets of a commercial laying hen strain reared until 18 weeks of age in groups of 15, 30, 60 and 120 (four replicates of each group size). Feeder, drinker, perch and litter space (i.e. floor space allowance) per bird, were constant across group sizes and all resources were continuously available. Even though the absolute numbers of birds performing the same behaviour at the same time or being located together at the same resource patch increased with increasing group size, the relative degree of synchrony of feeding, drinking, perching and preening across the whole flock decreased exponentially with increasing group size (P<0.001 for all behaviours) as did the relative degree of clustering at the same resource patch (P<0.001 for the same four behaviours). Preening was the most synchronous behaviour (more than twice that of the least synchronised behaviour, perching), and feeding the most clustered in space (three times more clustered than the other behaviours). These results imply that it is more important to provide sufficient resource space for all birds to perform daytime activities simultaneously when kept in the smaller group sizes typical of cages, than in the larger flocks typical of birds kept in floor pens and aviaries.