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North America

One continent on our planet changes more dramatically than any other. North America. Whole landscapes here can be transformed in a matter of minutes. And all life has to be ready to seize the moment. Getting it wrong can be disastrous. But time it correctly and there can be great rewards.

North America. This is a land of opportunity.

Over a hundred times of the size of Great Britain, North America stretches from just above the equator almost to the North Pole. Temperature can range from fifty degrees Celsius to minus forty. The coldest wilderness of all lies in the Arctic north. Here, in Canada’s Yukon Territory, winter is brutal. Many animals have travelled south to avoid the worst of the cold. For those which stay behind, life become very hard indeed.

A Canada’s lynx. No other kind of cat-anywhere-lives farther north than this one. The search for food can take him hundreds of kilometres. A snowshoe hare. This could be a chance. He’s lost the element of surprise. And now there’s a tangle of branches between him and his prey. Missed again. More of his energy wasted. Another hare, this time out in the open. And another failure. If he doesn’t kill soon, he may not survive these winter months.

But in North America, change is never far away. April, and billions of tonnes of snow and ice are starting to melt, bringing new opportunities. Much of the water drains southwards. Ten thousand creeks join, forming North America’s biggest river system. The melt-waters travel over three thousand kilometres down the Mississippi right through the heart of North America.

In the streams of Tennessee, river chub are getting ready to breed. This male is busy building a mound of stones in which-if he’s luck-a female will lay her eggs. As the river flows faster, the work gets harder. It’s a good start, but rivals are doing the same thing and want some of his pebbles. The intruder seen off and it’s back to business. A few finishing touches. And then with the last of some seven thousand stones, his nest is complete. And right on time, here is a female. But the mound now needs one last feature. A trench where she can lay her eggs. And with the gentle shimmy of his body, he nudges her into position. And she deposits her eggs where they will be safe from both currents and predators. His work is done. The eggs will hatch and then his mound will be slowly dismantled by the current. So next year, he will have to start all over again.

Spring is now well on its way. North America is wonderfully rich in wildflowers. There are over ten thousand species of them. Hummingbirds fly up from the south to feast on the nectar.

Along the North America coast, the tides are the largest in the world. The fragmented shoreline forces sea-water to rush up narrow inlets. And each time the tide retreats, it opens a freshly stocked larder. 18 thousand square kilometres of extra coastline is uncovered in the space of just two hours.

A mother black-bear is looking for something suitable for her cubs. This is their first ever trip to the seaside. In a few hours, the tide will return. So they must keep up with mum. Here’s something tasty, crabs. Big crabs can give a nasty nip. So it’s best to start off with smaller ones. During spring, three quarters of the bear’s food comes from the beach. But now, this family is not alone. An adult male, he is double her size and they are in his territory. The cubs know that call. It’s time to head safety. Bears have poor eyesight but their sense of smell is acute and the male has detected intruders. He know exactly which tree they are in. If the cubs stay up there, they’ll be safe. But they’re losing precious feeding time. For now he’s content to leave his scent mark. A warning note for trespassers. The family moves on. For the cubs, lunch today will have to be a take-away. The tide comes in, and within minutes, feeding time is over for another day.

As the continent warms, on a few special nights when the temperature is just right. The forests of North America put on a show. Male fireflies are taking to the air. These insects are not, in facet flies, they’re a kind of beetle. The light produced by the males is the most energy efficient on earth. Some species synchronise their flashes to increase the visibility of the message. If a female sees something she likes, she returns the signal. It looks as if the message is working.  But the forest is booby trapped by orb-weaver spiders. The firefly continues to glow even in death. Other males see the flashes-but not the danger. The spider’s larder is filling up. But for every firefly that gets caught, thousands avoid the traps. And this male is luck. He’s found a mate. And over the course of the night, millions will pair up.

There are over one hundred and fifty different species of fireflies in North America and each has its own flash code. Once they’re mated, the female deposit their eggs in the ground and for those that didn’t find a mate-their one chance has come and gone.

Little rain reaches the heart of the continent. For over two and a half millions square kilometres, there’s not a tree in sight. Many of those living here spend much of their time underground.

A prairie dog, a kind of large, burrowing squirrel. Sentinels keep watch ready to warn others of any danger. And at this time of year, there’s a new generation to protect. This mother has six pups. The youngster constantly beg for food. After all. The pups aren’t great at sharing. But the prairie dogs don’t have the prairies to themselves. An American badger. The pubs have never seen one before. And badgers eat pups. A burrowing owl. It also knows that badgers are dangerous. It too has young and does not want the badger anywhere near them. Eventually the badger gives up. He sets off to look elsewhere. If he can find a place where the grass is higher than he is, he will have a better chance. The mother sounds the alarm. Adults know the danger all too well. Four pups make it to safety below. But their mother dare not wait above ground any longer. Half of all prairie dog pups don’t survive to adulthood.

Predators are not the only problem faced by animals living on these great plains. Warm air sweeps up from the Gulf of Mexico and across the open prairies. And here, with no mountains to block it, it meets the frigid air from the Arctic. The results are spectacular. As the air currents mix and swirl, they build into one of nature’s most fearsome forces. Tornados. These twisters spin at speeds close to five hundred kilometres an hour-the world’s fastest wind. Over a thousand tornados touch down here every year.

These drenching summer storms are prevented from spreading westwards by the Rocky Mountains. Some peaks are four kilometres high. So beyond them to the west, much of the land remains parched. The great American desert cover over two and half millions square kilometres. Here, roasted by the sun and blasted by the wind, the rocks disintegrated, and mountains, particle by particle are reduce to sand.

These pillars are all that remain of a plateau once dinosaurs once roamed. Few animals can now survive here. In summer-as all deserts-the enemy is heat and it returns every day. At seven in the morning, the temperature is already 25 degrees Celsius. A clock is ticking for one unusual descendant of the dinosaurs. A road-runner（走鹃）, found only in the deserts of North America, build for a life on the ground. He can run at over 30 kilometres an hour. But the prey he seeks are one step ahead. The road-runner’s challenge is picking the right target. A Gila Monster, too big. By mid-morning, it will be 40 degrees Celsius. Even the smallest lizards will soon head for cover. A centipede. Slim picking for the morning’s work. Hunting should get easier and prey will stay out longer once the summer’s peak begins to fade.

On the east coast, summer is coming to an end. Cold currents are sweeping along the coast of Florida. And with them come grey mullet on their migration to their spawning grounds in the south. Millions of them and packed so tightly, they stain the water like an oil slick. Few people on the beach are even aware of them. The mullet keep as close to the shore as possible for in deeper water there are predators. Close to the beach, they have to keep clear of human swimmers. But now hunters from the open ocean have detected them. Tarpon over two metres long and weighing over a hundred kilograms. To get close to the mullet in the shallows, the tarpon turn on their sides. Now the mullet can’t see their shining sliver flanks until it is too late. And feasting begins. Black-tipped shark arrive. Pelicans join in. But these attacks have little effect on the immense shoals. The mullet outnumber their enemies by ten thousand to one. So the great procession travels on into the northern Atlantic ocean where at last they will be able to spawn in safety.

Autumn arrives in North America. No mountain range spans the continent from east to west, so there’s nothing to stop cold air from the Arctic sweeping down unhindered as far south as Louisiana.

Autumn brings colour to the southern swamps. Here, it has been hot and humid for most of the year and now these sub-zero temperatures are something of a trial for the local inhabitants. An American alligator. The alligator reacts to the chill by slowing its heart rate to barely one beat per minute. It’s a kind of energy-saving winter sleep. But other creatures don’t have this ability. The largest inhabitants of the swamp. A relative of the elephant. A manatee. A female provides milk for her calf from a teat behind her flipper. She might be able to survive the chill, but her calf cannot. So every autumn they need to find warmer waters. They have a long journey ahead, it could be hundreds of kilometres. And she is not alone. The warm waters they need to survive come from an unusual source. An immense underground river flows through subterranean channels in Florida’s rocks. In places it comes to the surface creating over a thousand springs. Now in the winter these spring are ten degrees warmer than the surrounding waters. So manatees comer here every year from far and wide. And here they can relax. They can get their backs scrubbed. And they socialize. No one is in much of a hurry. And young manatees have a chance to meet some surprising neighbours. In summer, playing with an alligator might be a dangerous game. But now-at any rate-the giant reptiles are still too chilled to react with any vigour. Without these warm pools, few of Florida’s manatees would be able to survive the winter. But the waterways here are very popular with people too. And many manatees carry scars inflicted by the propellers of boats. A calf has already had its first scrape. Every year more than a hundred manatees die from human causes.

As the human population of Florida grows, so wild life is coming under increasing pressure. Across North America, over four thousand square kilometres of wilderness are lost every decade.

But it is in the far north of the continent that human beings are affecting wildlife most critically. Canada is warming faster than any other country on the earth. Polar bears have always relied on sea-ice for their hunting. But summers are now getting longer and hotter. For most of polar bears, this is a time of starvation. On the shores of Hudson Bay, some bears are finding new source of food. They’re all looking for the same thing and they have their own ways of catching it. First, they must find the right rock. Now they must wait. The tide comes in, bringing with it other northern giants. Beluga whales. Close to the shore, their calves should be safe from ocean-going predators such as orca. Over 3000 whales have gathered here. The young male makes his move. Polar bears are skilled marine hunters and beluga are slow swimmers. As long as a whale can keep an eye on a hunting bear, it should be safe. This young bear is still learning. More experienced bears know to be patient. Success will depend on split-second timing. A bite at the back of the head, and the kill is swift. This extraordinary behavior has only been reported here in this remote corner of North America, and only in the last few years. This one small group bears has found an ingenious way of surviving the lean summer months. But for others, it is not easy. We continue to transform our planet and seasons are becoming less predictable. Will the wildlife of North America be able to adapt? Not only on this continent known for its change, but in a rapid changing world.

Dec 16, 2019

Version 1

By. MZL

Email：muzl0531@163.com