The motivation to perch is one of the strongest behavioural drives in laying hens; deprivation in caged systems causes chronic frustration and bone weakness.
Perching serves multiple functions: safety from predators, thermoregulation, and social spacing. The inability to perch in cage systems is associated with severe osteoporosis — reduced bone density from lack of weight-bearing activity combined with calcium depletion for eggshell production. At slaughter, over 50% of cage-reared hens have bone fractures. Perching also satisfies a strong behavioural motivation, and its thwarting causes frustration measurable through cognitive bias paradigms.