John Nettles explores the late naturalist Gerald Durrell's legacy as he follows the work of a small group of people trying to save endangered orangutans on Jersey and Sumatra.
The Taiga forest, on the edge of the Arctic, is a silent world of stunted conifers. The trees may be small but filming from the air reveals its true scale. A third of all trees on Earth grow here and during the short summer they produce enough oxygen to change the atmosphere.
Coral reefs are home to a quarter of all marine species. Survival in these undersea mega-cities is a challenge with many different solutions. A turtle heads to the reef's equivalent of a health spa - but she must use trickery to avoid the queue. A remarkable Grouper uses the fish equivalent of sign language to collaborate with an octopus, flushing their prey out of hiding holes. A metre-long, ferocious-jawed Bobbit Worm hides in its tunnel. Monocle Bream retaliate by squirting water to expose its sandy lair.