Wild Japan | A Peaceful Journey Through Nature In 4K | BBC Earth Relax

It's the breeding season and the trees are teeming with frogs. The female is with a male at the tip of a branch perched above the paddy pool. She's building a nest by whipping up a giant ball of foam with her back legs. She lays hundreds of eggs inside. She's attracting the attention of other males. Each male could still fertilize some of the remaining eggs in the foam. They're coming in from all directions. But the foam makes it hard to get to grips with the competition. Things quickly descend into an undignified wrestling match. This male's work here is done. It's time to move on and find other nests. But when you're covered in slippery foam, it's hard to leave with dignity. It's an unusual problem for a tree frog. As the days pass, the eggs develop in the safety of their foam nest. The temperature rises with the summer sun and the foam ball dries to form a protective case. The tadpoles inside are still moist and six degrees cooler. But the little tadpoles need rain. At this time of year, warm air is rising over the steep Honshu mountains and clouds are starting to build. The tree frogs have timed their nest building perfectly. After 20 days, conditions are just right and the waiting is over. The hard foam starts to dissolve and the tadpoles drop out straight into the nursery pool of the rice paddy below. They feast on the remaining pieces of the nest. A final meal before they take their chances in the big wide world. Their mother has pulled off a remarkable feat of planning. It's when animals leave the forest edge and move into farmland that the relationship with humans becomes less benevolent. The macaques of the lower forests are as bold as their mountain cousins and often venture out in search of new opportunities. There are all sorts of perils but there are rewards too if you're willing to take some risks. For over a hundred years, people have been growing the finest fruit and vegetables on these warm rich soils. For these cheeky thieves, it's irresistible. Growing perfect produce is a Japanese obsession. So the last thing people want is marauding macaques. As the day heats up, the farmers take a break. The coast is clear. They have to be cautious. If they're spotted, there'll be trouble. But every day they brave the electric fences. They know all the weak spots where they can stage their raids and they gorge themselves on the fruit of the farmer's labours. They are almost impossible to stop but the farmers are not prepared to give in. They bring out their secret weapon. Specially trained monkey dogs. The Japanese Shiba Inu is one of the world's oldest breeds and people have trained them to protect their crops against monkeys. There's even a Japanese saying that when people are fighting they're like a dog and a monkey. But the rewards outweigh the risks. They'll be back again tomorrow. It's only the warmth of the Kuroshio current that allows coral to grow this far north in the Pacific Ocean. The current also brings nutrients from the deep. There's one very small resident who never strays far from the reef. He's a blue streak cleanerass. And he leads a very busy life. He eats parasites and dead skin from other fish. But he has to wait for them to come his way. And right now no one is stopping long enough to give him as much as a nibble. But then he spots something worth chasing. A batfish. Like a customer at a spa, the batfish lies back and waits for attention. It opens its gills and the cleanerass bustles in to begin the treatment. The batfish even changes colour. Probably to make parasites more visible. Someone else has arrived at the reef. The batfish is abandoned. There's a visitor from the open ocean that's worth dropping everything for. A manta ray, two metres long, has come back to a favourite stretch of reef. He signals to the manta by flicking his tail. And the giant responds by unfurling itself for cleaning. The manta keeps its feeding lobes rolled up while it swims. But a thorough clean keeps them parasite free. This enormous fish would never visit Japan if it wasn't for the warmth that bathes the island chain. And the helpful services of this resourceful little rass. Sea snakes. At one time, these snakes' ancestors lived on dry land. They must still visit the surface to breathe. But they are beautifully adapted to life at sea. Hunting for fish around the island reefs. They have some of the most toxic venom of any animal, so they don't have many predators. But as they forage off the coast of one small island, their greatest nemesis is approaching. Yoko and Setsuko are hunters, and they have a fearsome reputation. These two 70-year-olds are on a shopping trip like no other. Yoko and Setsuko live on the tiny island of Kudaka. It's only four kilometres across, and with limited space on land, the locals look to the sea to provide. As the sun sets, the ladies' prey is approaching. On certain summer nights, venomous sea snakes move towards the island and gather in coastal caves, looking for shelter and fresh water to drink. But coming ashore on this island is extremely risky. It takes some nerve to wade in with no protective clothing. Sea snake venom can be 10 times more powerful than a rattlesnake's. Yoko has been hunting snakes for 40 years. It's a skill that's been passed down the generations here for at least five centuries. The snakes will be dried in this smokehouse, using a secret process known only by the hunters. Then they go into a special soup. The catching and eating of sea snakes is a very old tradition on the island of Kudaka, where the sea provides more than the land. She needs to put food in the mouths of her snakes There's a bitter winter coming, and if they're not well fed, her cubs won't make it through. This is a hard place to be a mum. The family is not alone. This peninsula is home to 200 brown bears. It's one of the most densely packed populations in the world. The salmon bonanza has attracted others here too. Nobody lives permanently in this remote part of Hokkaido, but one hardy group have special permission to stay here for some of the year. Hokkaido is Japan's second largest island, but the harsh conditions mean it's home to only 4% of its people. Shirotoko is one of the loneliest corners, where you have to live close to the wild. Brown bears can weigh 300 kilos and are not to be messed with. When bears and humans cross paths, things can get dangerous. But here, something astonishing has happened. For the fishermen, bears have become a part of everyday life. It takes some nerve, but the men live alongside them as equals. Tough characters, side by side, both dependent on the salmon run. The mother bear knows what she's doing. Survival is in her blood. Her ancestors came to Hokkaido from Siberia, and they walked here. 12,000 years ago, Hokkaido was joined to the Russian mainland. Siberian animals colonized it, before the sea levels rose, turning Hokkaido into an island. It's why the wildlife here is so different from the rest of Japan, and so well-equipped to face the coming winter. The sika deer have started creeping into the lush cultivated fields. It's a whole new world. These fields are brimming with specially sown grass, intended for cattle. But this herd always seems to be one step ahead, helping themselves to the best grass before it can even be cut. Every year, deer can munch their way through over 30 million pounds worth of crops. But some farmers have developed a live and let live attitude. The deer are reaping the benefits of Hokkaido's human landscape. In a place like this, it pays to be adaptable. In the warmth of early summer, the red-crowned cranes have moved into the farmland waterways, and they have a new family member. They traditionally nest in marshes, but most have been drained. So the cranes are raising their chick in an irrigation channel. All through the summer, the chick will be entirely dependent on its parents for food. The channel is teeming with insects, fish and frogs, but the parents can barely keep up with their gangly offspring's appetite. The family won't be able to move on until the chick can fly. In the meantime, they can't escape from surprise visitors. The sika deer have managed to wander right into the path of a pair of cranes with a weak old chick. Mum and dad work together to shepherd the chick to safety. And then a quick flash of the dagger-like beak to make sure the deer keep their distance. The parents' diligence has paid off. Their priority now is to feed their chick while times are good.