Case Study: Hibernation, Torpor, and Aestivation

Image Credit: Mackenzie Angell (Graphic Designer)

In cold environments, many mammalian species undergo a period of hibernation, a period which is defined by minimal activity and metabolic activity. The three different forms include hibernation, torpor and aestivation.

Torpor is carried out by many small mammals and birds, for example, the hummingbird. In very cold conditions, the increase in metabolic rate may be insufficient to maintain body temperature within tolerance limits. Torpor is a physiological state of decreased metabolic and physical activity, and it is a major adaptation that enables animals to save energy when food is scarce or when temperatures are too cold.

Aestivation is another kind of seasonal dormancy which is referred to as a long-term torpor, and animals undergo this in very dry conditions. For example, the Garden Snail retreats into its shell and seals itself off, some earthworms coil into balls wrapped in mucus, and Lungfish burrow in mud which hardens, which they remain in until the next rain season.

Other animals in very cold conditions may hibernate, spending a longer period in torpor. The metabolic rate during hibernation is low, to a level that just sustains life. The set point for temperature is lowered considerably, and is considered an excellent mechanism for reducing energy loss.