Nature’s Most Extraordinary Moments In 4K | A Perfect Planet | BBC Earth Relax

The red crabs. They've spent the dry season sheltering in damp burrows beneath the leaf litter through gills that must be kept moist. So it's only with the return of the annual monsoon that these land crabs can finally emerge. With the humidity now high enough they can begin an epic trek to the coast. Every red crab comes together from across the island and they do so in their millions. 50 million to be precise. Release their eggs that can only develop in the ocean. There's just one small problem. They may be crabs but they can't swim. They're scared of the sea so they don't have a choice. They must release their eggs on the highest tide. Each carries around a hundred thousand eggs so over just two or three nights trillions are released into the ocean. Though some are more successful. Once their work is done the crabs will return to the forest. Tortoise. These creatures can float and live without food or fresh water for long periods of time. This isolated atoll is the perfect refuge. Their only enemy is the sun. Without shade a tortoise risks being boiled in his shell. So after feeding in the cool of the morning and before the sun becomes too crushingly hot they have to find cover. All of them. There is very little vegetation but caves in the coral rock can provide the shade they so badly need. He's nearly there. All that is left is a white knuckle ride to the bottom. And he's in. Thousands of others are still out in the sun. This tree could shade a couple of hundred if they pack tight. Within an hour or so all must find shade of some sort if they're to survive. Safe. But the future for Aldabra's tortoises is far from certain. The climate is changing. Sea levels are rising and Aldabra's tortoises may soon have to find a new refuge or drown. Eden's whales have lived here for generations but the world around them is changing. Today agricultural pollution flowing from the land is beginning to suffocate this sea. Many fish now stay closer to the surface where the water still contain enough oxygen to survive. Eden's whales depend on these fish. They swallow huge quantities of water before filtering out their prey. It takes a lot of energy to drive their 15 tonne bulk through the water and with so few fish the rewards from feeding like this are barely worth it. So to survive here the whales have developed a new hunting technique that requires almost no effort. They simply open their mouths, the panicked fish jump right in. Swimming alongside another whale scares even more into the open jaws. With this ingenious new technique Eden's whales have found a way to survive the pressures they now face. All across the planet animals are having to adapt to a changing world but the speed of these changes will be too fast for many. If we could only halt our unrestrained plunder of the ocean its habitats and species would recover and at a time when our over-exploited lands are already failing us this has never been more important for humanity. Three weeks ago these mile-wide sandbars didn't exist. In another three months they'll be back underwater but now they provide a crucial opportunity for giant. They've been coming here precisely this time of year for generations. Fifty thousand of them, a quarter of the world's population. They're all here for one reason but their window of opportunity is short so timing is everything. Scaling the three meter high banks will take this female higher and drier than she's been for months. She's come here to lay her eggs but others have beaten her to it. The early arrivals have already claimed nearly every inch of the beach and there are still many more turtles to come. Whenever she turns the space is taken but being fashionably late does have an advantage. Had she arrived earlier her eggs might have been dug up by those searching for somewhere to lay. She's found her spot. Settling down she lays nearly a hundred eggs. Burying them keeps them safe from predators and the warm sand incubates the clutch. They must hatch before the river rises again and floods the sandbar. Any turtles that lay after her may have left it too late. Hopefully she has got her timing right. Two months on and the hatchlings emerge into the world. They were laid at the perfect time. Hundreds scramble for the river just as the water starts to rise. Those still to hatch aren't so lucky. He's a marine iguana. The only lizard in the world that gets its food from the sea. The seaweed on which he totally relies only grows in abundance here because of the nutrients brought by the Cromwell current. Once in the water he has just 30 minutes to find food. Any longer than that and his muscles will seize up and he'll drown. For like most reptiles he can't handle the cold. Chilly water isn't a problem for a warm-blooded cormorant. She can swim in it all day but can only hold her breath for a few minutes. He on the other hand completes his whole half-hour trip on one single breath. His flat face and sharp teeth make him an efficient seaweed cropping machine but with the clock ticking he must eat fast. The cormorant having caught its fish goes back to the surface. One last mouthful and it's also time for the iguana to head for home. But to stop his muscles from seizing up in the cold water he must get back quickly. So he could do without the attentions of an inquisitive sea lion. Dry land is now just 30 meters away but the biggest hurdle is still to come. The surging water now fights against him. He's out but he stayed in the cold so long that he's lost his strength and he's made it. This fire ant has reached the edge of her known world. Her way forward has now become blocked by the rising waters. She's one of many and in a few minutes their underground home will be submerged. Forced to evacuate workers and soldiers try to save the larval young. As their nest floods the colony seems to be doomed. From chaos comes order. The fire ants band together each locking legs with its neighbors. They're building a living raft. Each ant is covered in fine hairs that trap air against its body. As the raft forms this air creates a cushion for them all to float on. This is the power of the colony. By working together they've become unsinkable and gets left behind. Pulled from the shallows the colony is now at the mercy of the flood. Holding tight to the larvae and keeping their queen hidden at the center of the raft the colony drifts into deeper water where they're vulnerable to fish that now swim through the flooded forest. Those that lose their grip must get back to the safety of the raft.