Filmmaker Shane Moore and Assistant Cameraman Michael Mauntler recap on the time they spent on Alaska's Admiralty Island and discuss the challenges that come with filming bears in their natural environment.

Fortress of the Bears filmmaker Shane Moore on some of the filming techniques he used during his shoot on Alaska's Admiralty Island. A behind-the-scenes look at what goes into the making of a nature documentary.

Enter a world shaped by bears, trees, and salmon. Watch the full episode of PBS Nature's Fortress of the Bears.

Admiralty Island, part of the Tongass National Forest, hosts the largest concentration of brown bears in the world. Watch video.

After a spring and summer with no sign of salmon, a mother bear is desperate to catch fish to feed her famished cub. Watch video.

It's taken all spring and summer, but salmon finally return to Admiralty Island to spawn. Watch video.

Enter a world shaped by bears, trees, and salmon, and explores the delicate balance of their interconnected lives. Watch a preview of PBS Nature's Fortress of the Bears.

This grizzly bear is not sleeping. She's been in a state of hibernation since November.

Chris Morgan shares his thoughts on the recent case of polar bear cannibalism. "Each and every polar bear is facing increased every-day stress as a result of our warming planet."

Intelligent, adaptable and fierce, the polar bear learned how to survive in a place that offers few comforts to any creature.