Nocturnal animals in zoos face significant welfare challenges when lighting regimes fail to match their natural activity patterns, disrupting behaviour, physiology, and psychological wellbeing.
Nocturnal animal welfare in zoo settings has historically received less attention than diurnal species welfare, partly because these animals are active when visitors and keepers are absent. Lighting is the central welfare challenge: nocturnal species have visual systems adapted for low-light environments, with rod-dominated retinas that are overwhelmed and stressed by daylight-intensity lighting. Even 'dim' exhibit lighting that appears acceptable to human visitors may be intensely bright to adapted nocturnal eyes. Reversed lighting schedules - bright artificial light during the day to induce nocturnal behaviour during visiting hours - represent a compromise that, when well-managed, can allow species-appropriate behaviour during visitor hours. However, poor implementation can result in animals that are chronically disrupted in their circadian rhythms, with consequences for hormone cycling, immune function, and reproductive success. Species like pangolins and aye-ayes are so sensitive to light disturbance that their housing requires particularly careful management. Best practice involves species-specific lux level guidance, regular circadian rhythm assessment, and keeper training in nocturnal animal behaviour indicators.