Why Are Some Animals Nocturnal?

Staying awake at night and sleeping during the day is relatively common in the animal world. While this seems pretty strange to most humans (except for some of our ancient ancestors), there are plenty of advantages that make being nocturnal a smart evolutionary move.

Of course, it’s not that animals decide one day to switch their sleeping patterns. And truthfully, it’s almost impossible to truly say why a given trait arose. Here are some of our best theories for why some animals are nocturnal.

Why Are Some Animals Nocturnal?

• There are fewer predators out at night. The vast majority of nocturnal animals are birds, insects, and mammals, not reptiles. A leading theory for why animals are nocturnal is that this trait evolved as a way to avoid being eaten by dinosaurs and other top predators back when mammals and birds started to expand as groups.
• It’s easier to avoid detection at night. While many nocturnal animals have heightened senses of smell and hearing, it’s still a bit easier to avoid detection at night. The darkness helps both predators and prey move around a bit more stealthily. Prey animals use the cover of night to forage more safely, while predators capitalize on the same darkness to ambush prey more easily.
• There are prey animals out at night. If you’re a predator who specializes in eating small mammals, there’s no better time to be outside than nighttime. Predators are generally more successful if they hunt while their prey is awake and mobile – so many predators hunt at night to match their prey’s schedule.
• There’s less competition at night. Some nocturnal species likely developed this schedule as a way to reduce conflict over food sources. If everyone else in the neighborhood heads to the watering hole and the grazing field in the morning, perhaps it’s helpful for you to go during the off times.
• Nighttime is cooler. Many desert animals are nocturnal for the evident reason that this helps them avoid the heat of midday. In scorching-hot parts of the world, being nocturnal is simply a good move. Water conservation is also an important aspect of avoiding the heat of the day. Moving around when it’s cool and dark avoids overheating and wasting precious water.

Many nocturnal animals are probably active at night for a combination of these reasons. Evolution is a slow process, and it’s almost impossible to say exactly which pressures caused each species to evolve in a given direction.

Special Adaptations of Nocturnal Animals

Nocturnal animals also have special adaptations to help them get around in the dark. Unlike humans, they generally don’t rely on their sight as their primary sense. Instead, they get around thanks to sensitive ears, whiskers (to sense nearby objects), and smell.

Of course, many nocturnal animals also have large eyes that are specially adapted to excel in low-light conditions. This is especially true for birds and nocturnal primates, which need to be able to see branches to land. Some animals, like cats, can see well both in daytime and at nighttime. Others, such as bushbabies and bats, have poor eyesight in the light.

Threats to Nocturnal Animals

Light pollution is a huge threat to nocturnal animals. Lights from cities cause changes in migration patterns and can confuse animals. Light pollution is a major problem for sea turtles and nocturnal migratory birds because they use starlight as a compass.

Human activity and disturbance are also pushing some animals to become more nocturnal. Read more about that here.

Climate change is also making some areas of the world much hotter and drier than they used to be, potentially pressuring some animals to become more nocturnal or crepuscular (preferring to be active at dawn and dusk) than they are currently.