The ability to express natural behaviour is one of the Five Freedoms and a cornerstone of welfare assessment. Understanding what natural behaviour means for different species is essential for meaningful welfare standards.
Freedom to express natural behaviour is not a luxury for farm or zoo animals — it is a fundamental welfare requirement rooted in evolutionary biology. Animals have behavioural needs as real as their nutritional or thermoregulatory needs, and chronic prevention of these behaviours causes psychological suffering that is increasingly well-documented. The challenge for welfare standards is specificity: natural behaviour for a pig (rooting, wallowing) differs entirely from natural behaviour for a layer hen (dust bathing, perching, foraging) or a dairy cow (grazing, lying on pasture). Generic environmental standards cannot substitute for species-specific requirements. The most rigorous welfare frameworks assess whether each species can express its key motivational behaviours — not whether conditions are abstractly "good enough."