短尾矮袋鼠

On the western edge of Australia, perched on the fringe of the continental shelf, lies a chain of extraordinary islands. Islands and their waters teem with life. Curiously, the world here seems to be upside down. The seasons are reversed. Summer, not winter, is the time of hardship. Trees shed their bark instead of their leaves, and ocean currents flow. Even the evolutionary rulebook seems to have been turned on its head. One island in the chain has become an unlikely stronghold for penguins, for deadly tiger snakes, both of which would appear to be totally out of place. But the most remarkable island is the realm of the quokka, a small wallaby species found in western Australia and nowhere else on the planet. Quokkas are famously known as the happiest animal on earth, but in this series, their secret real lives will be revealed. How they survive prolonged drought, crippling food shortages, have evolved extraordinary breeding strategies, and the surprising violence of the fight to ensure the survival of their dynasty. This is Rottnest Island, kingdom of the quokka. The story of Rottnest is inextricably linked to the quokkas. They even gave the island its name. Although the name quokka actually comes from the local aboriginal Nyuma word, when Dutch explorer Willem de Flamming visited the island in 1696, he mistook the quokkas for giant rats and named the island Rottnest, meaning rat's nest in the Dutch language of the time. But it's not that long ago, in geological terms, the mere blink of an eye that Rottnest and its island neighbours didn't exist at all. Just 7,000 years ago, the islands were still part of the mainland. Then, as the sea levels rose, things began to turn mysterious in the island chain. Even though the islands are close together and were formed at about the same time, they could hardly be more different. It would appear that once the islands separated, nature went about dividing up the real estate equitably, giving it to the animal most suited to adapting to each environment. This is no more apparent than on Rottnest, the kingdom of the quokka. If you research quokkas, you'll most likely find them described as their happiest animal on earth, probably because their faces often appear to be smiling. But the truth is that these little creatures, only about the size of domestic cat, are contenders for the title of the toughest animal on earth, because all the odds here are against them. Evolutionary theory says that isolated island populations are more vulnerable to factors that lead to extinction. The quokkas defy that theory. Quokkas are unique to Western Australia, and on the mainland, they're one of Australia's most vulnerable marsupials. But on Rottnest, they thrive. More than 10,000 live here, making this tiny island home to well over half the world population. To compound things, the quokkas live in conditions that would actually appear to be a barrier to their well-being. Rottnest Island is around 19 square kilometres of limestone outcrop. Inland, the main habitats are wetlands centred on salt flakes in the northeast, scrub heath towards the west, and woodlands in the centre. It may look lush, but surprisingly, it isn't if you're a quokka dependent on the habitat for your existence. The life of quokkas has never been filmed so closely. So, we'll follow this colony who live in the central woodlands to see just how it is they withstand the hardships they face. Life on Rottnest Island may be difficult, but offshore, it's a different story. The ocean in this part of the world has a spectacularly rich food chain. It begins with the seagrass meadows. Up to 10 species of seagrass grow here. Carbon is critical to all ecosystems, and seagrasses are 35 times more efficient at sequestering carbon than rainforests, underpinning the food chain. The key to all of this is the Lewin Current. In keeping with this unusual place, the Lewin Current is upside down. Everywhere else in the world, currents on the western edge of a continent are either cold or flow north. The Lewin Current is warm and flows south. This warm water creates the ideal conditions to see grasses. It even allows tropical corals to grow this far south. Rottnest's coastal waters also provide prime pickings for another of the island's most successful species, ospreys. Like the quokkas, ospreys on Rottnest Island buck the evolutionary trend, with a population density here 10 times that of the nearby mainland. This pair are longtime residents of Little Salmon Bay in the south of the island. Ospreys are supremely adapted to hunting fish from the air. The male looks for fish swimming close to the surface. Ospreys can see prey from 40 metres up. He spots the fish. He can hit speeds of 80 kilometres per hour in the dive. Ospreys have even been killed misjudging the depth of the water and hitting the reef. He completely submerges. Ospreys waterproof their plumage with oil from a gland at the base of the tail, and he simply shakes the water off. The ospreys' talons are extraordinary fishing tools. Their feet have barb-like scales on the underside to grip the slippery catch, and their outer toes are reversible, allowing them to have two claws pointing forward and two backwards, giving a secure grasp on the fish. Unlike most other raptors, ospreys are very careful about aerodynamics, so to help, in flight they align the fish with its head forward. Ospreys can easily take fish equal to their own body weight, around two kilograms. The male takes his catch to a feeding perch he set up near the nest. Rottnest is the jewel in the crown, but the animals of the rest of the island chain are also strange and unlikely. Less than 20 kilometres away from the quokka's home on Rottnest, Karnak Island is a serpent heaven or hell. The island is small, only 16 hectares in area, yet it's estimated four to five hundred deadly tiger snakes live here, giving it one of the highest densities of venomous snakes on earth. Here they've become monsters. They can be twice as heavy as the tiger snakes on the western Australian mainland, and as part of what seems like the island chain's grand evolutionary experiment, the tiger snakes here have evolved to thrive, despite the environment appearing to be just the opposite of what they need. Karnak's remarkable residents also include a population of native Australian sea lions. This is the rarest sea lion species in the world, and the only one found solely in Australia. Karnak is the ultimate sea lion bachelor pad. All the animals found here are males. They use the island as a haul out during the non-breeding season. Further south is Penguin Island. Over a thousand little penguins live here. They've spent the day hunting at sea, and they return after dusk. This is the most northerly colony of little penguins in the world. Perhaps their most spectacular evolution allows a bird apparently designed for the frigid Antarctic to survive summers of 40 degree plus heat. For much of life on earth, it is the cold, hard winter months that are the time of hardship. But in the upside down world of these islands, it is the brutal summers that are the hardest to survive. With temperatures edging 40 degrees centigrade, the crested terns are trying to feed their chicks. It's a scene of chaos. In blasting wind and baking sun, chicks desperately try to find their parents. If they approach the wrong adult, they are brutally turned away. Some are harassed and attacked. Over the course of the day, many will die. But the harsh summer begins to reveal just how hardy the quokkas of Rottnest are. The summer heat destroys the most precious commodity of life, water. As the water in their home range dries up, the woodland quokkas begin to feel the pinch. They guard their share aggressively. Thirst makes even the joeys arc up, even though they aren't really in the right weight division. As the daytime heat becomes unbearable, the quokkas seek shelter and try to sleep through it. Quokkas are mainly nocturnal, and at nightfall, they'll head out in search of water. They'll travel unseen, using runs and tunnels they've worn through the woodlands. For the first time, night vision cameras reveal their activities. The woodland quokkas have traveled to the edge of the salt lake. Here, they've uncovered a fresh water seep. It's only a trickle, but it's precious. The fights for a fair share continue. It's every animal for itself. This quokka continues its quest for water into the day. It's feeding on samphire. At this time of the year, samphire is a poor source of nutrition, but it's a succulent, so each mouthful contains a small amount of water. For some quokkas, this could be the only source of hydration for weeks on end, but remarkably, they're capable of surviving on just this. As the summer wears on, things become increasingly desperate. The quokkas are back on the edge of the salt lake looking for fresh water, but the seeps have dried up. In desperation, this animal takes a drink. It could be trying to sift out a fresh water layer floating on the surface, or this may be the first time a quokka has been filmed drinking salt water. If the quokka is drinking salt water, it shows just how resilient the little creatures must be. This water is four times more saline than the ocean. In most mammals, this starts a vicious circle as the kidneys produce more urine to expel the excess salt, leading to further dehydration and eventually death. It's not only drinking water that's scarce, food is a problem for quokkas all year round. The island's poor salt-laden soil means the plants lack nutrition. Quokkas eat for most of their waking hours, but even so they battle malnutrition all the time. The woodland quokkas glean what they can from the sunburned vegetation. As summer wears on, plants produce less and less of one essential nutrient, nitrogen. Nitrogen is critical to the quokka's ability to produce iron in their bloodstream. As nitrogen levels drop, the lack of iron results in many of the animals developing acute anemia and mortality rates in the quokkas shoot up at this time of year. Nearby, an older joey is sleeping fitfully. It could almost be dreaming of fresh food and water. Now severely anemic, this animal is one of those at the highest risk. Studies of the skulls of quokkas that succumb to the summer die-off show that most deaths are in animals that are about a year old. A sudden rainstorm lashes Rottnest. The weather's broken and temperatures drop. The quokkas are now at their lowest head. Some are too exhausted even to drink the life-giving fresh water. Many won't make it. The storm isn't bad news for every animal here. The surf's up and the local population of dolphins are determined to make the most of it. They don't appear to do this for any purpose. Like humans, it's just for the fun of it. They make full use of the perfect waves caused by huge swells from the west hitting the island's reefs. The cooler weather signals the start of the breeding season. The ospreys are busy rebuilding and repairing their nest stack. The birds pair for life and reuse their nest stack each year. Over two metres round and a metre tall, this one has probably been used by many pairs and could be 75 years old. But they also have a problem. Last year's chick, now a fully grown juvenile, is reluctant to leave their side. The pair won't want it around when the breeding season starts and there's no need for it to stay here. The juvenile is now a successful hunter in its own right and is perfectly self-sufficient. Eventually, the male's patience runs out and he's forced to take action. Finally, the juvenile has got the message. Although it seems, it's not impressed. At Karnak Island, the Australian sea lions are also getting ready for the breeding season. In this all-male colony, the sea lions engage in a strange pre-mating behaviour, where the older, bigger animals assert themselves over the juveniles in a balletic show of sexual dominance. They don't mate here. They'll migrate to join the females at their breeding islands, about 200 kilometres north, staying there for four or five months. Ashore at Karnak, the tiger snakes are one of the few creatures that don't thrive in the cooler temperatures. They are preparing to brumate, a period of dormancy similar to hibernation in mammals, but in reptiles it doesn't involve a long period of uninterrupted sleep. It's not known how or when the tiger snakes came to Karnak. They may have swum here or been isolated when the sea rose. One story goes that a snake showman called Rocky Vane released the first tiger snakes here in the early 1900s, after his wife was bitten and died. If they really have only been here just over a century, their adaptation to this environment has been meteoric. On the mainland, tiger snakes commonly live and get most of their food in wetlands, but there is almost no fresh water here. To have been able to adapt swiftly enough to survive this lack of water, the tiger snakes have shown remarkable physiological and behavioural flexibility. On Penguin Island, the penguins have mated and this female is incubating her eggs. Little penguins usually establish a secure burrow to nest in, but these have chosen a nest box placed here by researchers. The penguins share the duty of tending the eggs by alternating, with one parent on the nest while the other forages at sea. The female is waiting for her partner to come back, so that she can take her turn at sea to feed. Winter weather hits the islands with its full force. Exposed on three sides, these islands are some of the windiest places in Australia. For the quokkas, the cooler weather is a welcome respite. Now, at least, they have water. But food is still a problem. In winter, less sunlight reduces photosynthesis in plants. Despite the water encouraging the plants to grow, they're no more nutritious. So, the hardy little quokkas have adopted ways of foraging that are unusual to most marsupials. One climbs a Rottnest Island tea tree to get at the best shoots. It seems quite at home up here. It's been suggested that quokkas belong to the same family as tree kangaroos, but separated by the entire continent, the nearest wild tree kangaroo population is almost three and a half thousand kilometres away. If they are related, it becomes even more of a mystery as to how the quokkas ended up isolated in this corner of southwest Australia. As the quokkas forage, it appears that some are most definitely not related to tree kangaroos. Quokkas have another trick up their sleeves to get maximum nutrition from the plants. They swallow some of the food without chewing it, where it's broken down by partial digestion. The quokkas regurgitate it and eat it as a cud, extracting many more of the nutrients. Although it seems that sometimes, this can come at a price. In the water's off Rottnest, this is a spectacular time of year. A humpback whales are passing by on their migration north. They've spent the summer feeding in Antarctica and they're now heading for the breeding and birthing grounds off the Kimberley coast of northwestern Australia. A round trip of 13,000 kilometres, this is one of the longest migrations of any animal on earth. Many of the females are on an express trip to give birth to calves conceived in the Kimberley last year. But the rest of the adult whales are on a mission to find a mate. Male and female humpbacks use sound to attract attention and the ocean off Rottnest Island begins to echo to their communications. These huge percussive sounds travel great distances under the water. So does the male's song. Some of the whales have paired up. Their interactions culminate in a sight seldom caught on camera. This is a likely mating or attempted mating. The woodland quokkas are also ready to breed. The mood in the colony has changed. It's not known if this sniffing behaviour is the quokkas checking each other to see if they're ready to mate. But as the females enter oestrus, it increases. The males begin to signal their readiness to mate by marking anything they can find with urine. Some of the males begin to show aggression, at first directing their attention to local flora. As the time for mating gets closer, the males begin a struggle for dominance and they turn their aggression on each other. One male seems to be actively seeking trouble. Eventually it really kicks off. Quokkas can be surprisingly vicious. A favourite method of attack is to latch on tight with their teeth and then claw away at their victim. This can leave nasty wounds. Other animals simply fight, like little furry ninjas. The osprey pair are first to actually mate. Nobody understands exactly why, but they don't mate in the main nest stack. They use a secondary nest close by. The secondary nest isn't used for raising chicks, but the birds often interact here and sometimes use it to eat their catchers. In about a month, the female will lay two to three eggs. Although they've successfully mated, the osprey pair continue to mock mate. The male lands on the female with his talons carefully clenched so he doesn't injure her. It's thought that this reaffirms their lifelong bond. The male quokkas too are now really gearing up to mate. They begin to follow the females closely. Some females still have older joeys and they reject the male's advances. Other males doggedly continue to pursue a female. It all seems to be utterly exhausting. Apparently the strain has become too much for this male and he falls asleep on the job. Finally, they do mate. If the mating is successful, in 27 days time, the female will give birth to a single joey. On Penguin Island in the nest box, the female's partner hasn't returned for some days. She's held on as long as she can, but faced with starvation, she has only one option. She abandons her eggs. She heads out to sea to feed and ensure her own survival. The eggs will not survive. Back on Rottnest, members of the woodland quokka colony face an uncertain future too. Like many, this female is exhausted. The mating season is gruelling and her body condition will deteriorate further in the lead up to giving birth. It'll be a battle to survive the rest of the winter. Only time will tell how many make it.