<p>Galapagos giant tortoises rest in a pool of mud in Volcan Alcedo’s crater on Isla Isabela. Many animals are nocturnal to avoid the heat of the day.</p>

Galapagos giant tortoises rest in a pool of mud in Volcan Alcedo’s crater on Isla Isabela. Many animals are nocturnal to avoid the heat of the day.

Photograph by Thomas P. Peschak ,Nat Geo Image Collection

Photos Reveal the Hidden World of Animals at Night

While some animals settle down as the sun begins to set, others are just starting to come alive.

Owls aren't the only animals that become active at night.

In fact, many animals are nocturnal—getting more active and beginning their day as the sun sets. There are a number of reasons different species are active at night, but many animals have evolved nocturnal habits to avoid heat.

Among the animals that prefer cooler nights are species not often photographed in the dark. Hippos and lions, for example, while commonly pictured roaming sunny safari fields, are often active long after the sun sets.

Walk around at night in the more untamed regions of the U.S., and you might see a more varied roster of wildlife than you would during the day. Gray foxes traverse Texas forests and beavers go to work in Grand Teton National Park when night falls.

Night is also when American cougars prefer to travel. The big cats have been pictured slyly traveling through the Hollywood Hills at night, mere miles from the sprawling Los Angeles urban area sitting below.

Having a dark night sky is more than just an opportunity to be covert for many animals. Light pollution from human-made structures can disorient some nocturnal animals, interfering with their navigation and making it difficult for them to see. Newly hatched sea turtles, for example, use the moon and stars to reach the ocean.

Look through the gallery above to see how animals live when the lights are off.

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