Why Mammals Sleep and How Much

by Helen Zhang, age 14

Adult mammals sleep for varying numbers of hours per day. However, sometimes these numbers can be drastically different among species. Recent studies show that there is a relationship between average sleep and an animals’ survival needs.

For example, a cow sleeps just four out of every 24 hours of the day. On the other hand, the little brown bat sleeps 19.9 hours. Why? Jerome Siegel, a UCLA sleep researcher, is convinced that these variations are based on the different ways animals have adapted to be energy efficient and stay safe.

According to Siegel, the number of hours spent sleeping per day depends on how much a mammal needs to eat. Based on this idea, the little brown bat sleeps more in order to conserve energy, except at night when it hunts for food. On the other hand, an elephant sleeps only three hours. Due to its large size, this makes sense because it eats most of the time.  

        How long an animal sleeps also correlates with safety. Mammals that sleep in hiding tend to have longer, deeper naps than those sleeping in the open. Mammals sleeping in the open have a higher risk of encountering predators. This leads the latter to sleep briefly and much more lightly than animals that sleep in hiding.

Although most mammals have distinct sleeping habits, these habits have a lot to do with survival instinct and self-protection.

[Source: National Geographic]