Journalist Kieran Mulvaney became fascinated with polar bears a decade ago when he was in Alaska on assignment. His new book is called "The Great White Bear."
A zoologist has found the smallest frogs known to exist in the world, just a third of an inch in length, in the rainforests of southeastern New Guinea.
Gray wolves returned to Yellowstone 15 years ago. Amid controversy, scientists say these top predators are keeping elk at bay and helping ecosystems flourish.