Spatial distribution and behaviour of laying hens housed in an alternative system

The spatial distribution and behaviour of perchery housed laying hens were compared at a constant stocking density (18.5 birds/m(2)) in eight pens with colonies of five different sizes (323 birds (N=1), 374 birds (N=2), 431 birds (N=2), 572 birds (N=1) and 912 birds (N=2)). The birds were placed in the perchery when they were 12 weeks old. Observations began when they were 26 weeks old and continued at 8 week intervals until 61 weeks of age. Colony size did not appear to affect the spatial distribution of birds, but more standing behaviour and less feeding behaviour were observed in the smallest and largest colony sizes. Older birds spent more time on the floor areas and less time on perches. Young birds (26-28 weeks) spent more time feeding, foraging, drinking and preening, and less time standing idle than older birds. In the afternoons, there were fewer birds on the perches and more on the floor levels, corresponding with less time spent resting and more time spent performing active behaviours. Birds did not distribute themselves evenly throughout their pens: within specific areas of pens densities varied between 9 and 41 birds/m(2). This variation, which reflects the flux of birds from one part of the pen to another, was greatest for the larger colony sizes, and may have adverse implications for welfare in terms of crowding and hysteria.