A tiger walks the same worn groove along the edge of its exhibit like a broken record. A parrot methodically plucks out its ...

We're all familiar with the idea of a sleep cycle. For people, sticking to a schedule helps our internal clock stay accurate, letting us sleep when it's time for bed, eat at mealtime and stay awake ...

Sign up for CNN’s Wonder Theory science newsletter. Explore the universe with news on fascinating discoveries, scientific advancements and more. Giant pandas living ...