housingA total of 180 beak-trimmed 16-week-old Isa Warrenhens were randomly assigned to 12 experimental pens(2 m × 2.6 m) in groups of 15 individuals. The hens wereinexperienced with nest boxes and had by the age of 16weeks not reached point of lay. In each pen five nest boxesof identical design were placed 95 cm above the ground.In front of each nest box there was a 15 cm deep platform,which could be accessed from a five-step ladder that alsofunctioned as perches. All steps were as wide as the totalwidth of the nest boxes. Each group of hens was visuallyseparated from their neighbouring groups, except when on