Every summer in the seas of Alaska, humpback whales, sea lions and killer whales depend on an explosion of plant life, the plankton bloom; it transforms these seas into the richest on Earth, but these animals may not survive to enjoy the great feast.

The great flood in the Okavango turns 4,000 square miles of arid plains into a wetland, drawing in millions of animals including elephants and hippos.

A look at the sardine run, which happens each winter along the South African coast, and the predators that wait for them.

The cameras follow the moving story of one lion family's struggle to survive until the return of the great migration; as weeks turn to months, the pride members become frailer, and the number of cubs dwindles from seven to two.

An amazing look at the annual return of millions of salmon to the streams where they were born; the survival of North American grizzly bears depends on this natural event.

The summer melt of Arctic ice provides opportunities for millions of animals, but grave dangers for others, including polar bears.

The planet is teeming with myriad life forms, both plant and animal, all interlocked in a struggle for survival. As time goes on, some living things are forced to adapt and change to survive. This series chronicles some of the most unusual, if not downright bizarre, behaviors that living organisms have devised to keep their species alive. The 11-episode series was four years in the making, taking camera crews to every continent and habitat.

David Attenborough journeys across the polar regions of our planet.

Produced by the team that created BBC's "Planet Earth" series, "The Hunt" explores the relationship between predators and their prey. Sir David Attenborough narrates this documentary while the cameras follow the animals in their natural habitats. With a specific focus on strategy, the hunters are examined in detail -- from their use of the environment to their sharp instincts and physical prowess. On the other side of the fence are the hunted, which use their senses and defense tactics to flee when they feel threatened. Each episode centers on a different habitat, and the last one focuses on the state of the planet.

Dazzling, state-of-the-art high-definition imagery highlights this breathtaking documentary series featuring footage of some of the world's most awe-inspiring natural wonders -- from the oceans to the deserts to the polar ice caps. Actress Sigourney Weaver narrates this American version of the original BBC production.

The planet and its wildlife.

Whenever documentary filmmakers at Discovery Channel and the BBC unite for a project, stellar television seems to follow. "Planet Earth: Africa" stems from this collaboration, as did the breakthrough natural history series "Life" in 2009. David Attenborough narrated that one, and he's back to take viewers on a journey through the vast and diverse continent of Africa. Four years in the making, during which more than 2,000 hours of video were shot, the program consists of six hour-long episodes that feature an array of never-before-filmed species, animal behaviors and previously unknown places. Cameras uncover the extreme dangers of the Kalahari, the dense forests and snow-capped peaks of the Savannah, the dynamic Congo rainforest, the ever-changing climate of the Cape and the massive and parched Sahara.

The nature series "Life Story," a collaboration between BBC and The Open University, shows how animals try to overcome the challenges they face throughout their lives to eventually continue their bloodlines by having offspring. The show, narrated by Sir David Attenborough, aims to give viewers an idea of what it is like for animals who face difficult choices in nature. Episodes document the journey of animals surviving the hazards of being young through learning how to survive as an adult, climbing the social ladder, getting a mate and becoming a parent.

"Dynasties" is a documentary by Sir David Attenborough as he goes on a journey behind some of the most celebrated and endangered animals on the planet. Follow the stories of penguins, chimpanzees, lions, painted wolves, and tigers. Each of these animals is locked in a heroic struggle against the forces of nature and their rivals -- they face harsh environmental conditions, dangerous predators, and even the greatest threat: humans. They actively seek to fight for their survival and the survival of their families -- their dynasties.

Sir David Attenborough narrates this critically acclaimed series that dives deep into the marine environment of Planet Earth. Although two-thirds of the world's surface is covered with water, scientists know less about the oceans than they do about the surface of the moon. This limited series travels from various coasts to the poles to examine watery denizens ranging from the gigantic blue whale to microscopic coral polyps.

Madagascar is a land just off the coast of Africa that is full of misty mountains, tropical rainforests and spiny desert scrub. It is also home to strange wildlife, much of which is not found elsewhere on Earth. This documentary series, from the BBC's Natural History Unit, showcases the island's diverse and rare wildlife, some of it being filmed for the first time. Among the animals featured on "Madagascar" are lemurs, frogs that change color from brown to yellow, wasps that pluck tadpoles from trees and fish that swim upside down. David Attenborough narrates the three-part series.