Thermoneutral Zone

The thermoneutral zone is a specific temperature range at which an endothermic animal's body can maintain at thermal equilibrium with its surroundings and at a stable internal body temperature without having to alter metabolic heat production. The animal is able to thermoregulate by altering the circulatory system alone. A thermoneutral zone is defined by two bounds, the upper and lower critical temperature. Below the lower critical temperature the animal must increase metabolic heat production beyond the basal rate. This ensures that heat production matches and therefore cancels out heat loss, in order to reach and maintain a constant body temperature. At some point, the animal reaches its maximum heat production rate and beyond this point, the animal's body temperature begins to fall and the animal is at risk of hypothermia.

Conversely, beyond the upper critical temperature of the thermoneutral zone the animal increases their metabolic rate to support increased evaporative heat loss using mechanisms such as sweating or panting. If evaporative heat loss is not sufficient to balance heat gain (e.g. due to air humidity or too high temperatures), the body temperature will rise to dangerous levels, leading to death by hyperthermia.

Figure 1. The Thermoneutral Zone.