"This is a first for me." "I'm standing in the forests of Mexico where every year 50 million butterflies assemble to spend the winter together." "It's something I wanted to see ever since I first heard about it." "And this is just the first of 12 places I'm going to visit in order to celebrate in this program some of the most spectacular sights that the natural world has to offer." "A new Millennium and the biggest party the world has ever seen" "As humans we traditionally punctuate our yearly cycle with mass gatherings so too do many animals, coming together in huge numbers for a whole variety of reasons" "Across the northern hemisphere and the south, every month around our planet, nature throws its own massive parties" "minus 6, 5, 4, 3, 2, 1" "We have ignition and we have lift off and the shuttle has cleared the tower" "Technology originally devised to help us see beyond our planet into space is now of invaluable use in discovering more about our own home" "Using the orbit of the shuttle as a guide, we'll make a month by month journey around our planet seeing how the sun and seasons influence nature's greatest spectacles" "We begin in the northern hemisphere at the winter refuge of Monarch Butterflies" "It seems extraordinary that during the secone half of the 20th century when we were exploring space and men were walking on the moon, the outside world knew nothing of this wonderful spectacle, it wasn't discovered until 1975" "and then thankfully, immediately protected" "But there are still a lot we don't know about the way in which these butterflies behave but one thing is certain, the trigger that sends us on these extraordinary journeys are the seasonal changes that are brought about by the way our planet the earth rotates about the sun" "Most great assemblers are driven by the search for food or the eternal need to reproduce" "For monarchs, it's a response to winter conditions further to the north and someone have flown as far as 4000km to be here" "Mass gatherings like this one are uncommon in the natural world and as we shall see many are short-lived" "Monarchs cluster together to keep warm, for even here the days and nights can be cold" "but on sunnier days, the dense clusters are in danger of overheating" "Taking to the air helps them to cool down and gives them an opportunity to exercise their wings" "while monarchs may occasionally drink, they will not feed much if at all during the winter and with extreme cold persisting further to the north, these butterflies will remain in this forest for several months" "It's the far north that is home to our next spectacle" "We journey to Newfoundland where both sea and land are frozen" "Caribou are north America's long distance walkers, spending their entire lives on the move" "This far north the winter days are short and the caribou use the daylight hours to search for food" "This winter herd consists mainly of females and calves" "They are part of the bigger George river herd, Canada's largest which numbers an impressive half a million" "When not moving, caribous spend much of the day with their heads buried in the snow the males have lost their antlers but the females keep theirs throughout the winter" "As mothers they need to be able to protect their excavations for beneath the snow they find a lichen known as reindeer moss which is rich in energy and the main winter diet for them and their calves" "Unlike other deer, a caribou muscle is completely furred, a necessary protection against frostbite and their legs have a build-in arterial bypass that keeps heat in the upper body where its most needed" "The herding instinct increases with the lengthening days and the caribou become more purposeful in their travelling" "This is the start of the great migration as they prepare to leave their wintering grounds and journey towards the open tundra" "As the George River herd moves northwards, and different strains come together, winter loosens its grip, spring is approaching" "On the other side of the northern hemisphere," "Japanese red crested cranes patiently sit out the last few days of winter" "Japan's most northern island Hokkaido experiences the harsher side of winter" "Unusually for cranes, they do not migrate despite temperatures of minus 20 degree Celsius" "Instead they follow a traditional daily routine that brings them to regular feeding sites" "Cranes live in communities throughout the winter but like most animals in the northern hemisphere the long awaited arrival of spring will cause a shift in the pattern of their daily schedule" "By mid March a strengthening spring sun is enough to stir some activity and shake off the winter blues but such early morning sessions provide only a hint of what is to become" "For these cranes, the ritual of flying to feeding sites is no different in spring" "Japanese cranes are heavy birds, males can weigh up to 15 kilos" "Flying into the wind helps them to get airborne, but with feeding sites just a few km from their roosts, they rarely fly higher than they need to" "Display is central to the life of these birds and the feeding grounds become the stages on which the Japanese cranes can do the thing they do best - dancing" "Cranes form lifelong partnerships and dancing strengthens the bond between them but it's also an opportunity for each pair to show off to the neighbors" "While for the cranes the problems of winter are over, another animal has had a very different winter experience" "Like the cranes red-sided garter snakes patiently wait out the long winter, but unlike cranes they do it underground" "10 feet underground in fact" "In all, they have spent 7 months beneath the Manitoban prairies and their blood has congealed to the thickness of mayonaise" "The males are the first to react to spring and despite the remains of some winter snow, they emerge from deep underground" "In a matter of days, they appear above the surface in their thousands" "Under the warmth of an April sun, the blackness of their stripes helps them to heat up more rapidly" "Having spent so long underground, the males have lost a third of their body weight, but before feeding they must mate" "Their test-osterone levels are at an all-time low but this does not deter them" "Sperm produced the previous summer has been stored in their bodies throughout the winter and this is their one and only chance to use it" "The females are 3 times the size of the males but what the males lack in size, they make up for in number" "It's not unusual for a single female to court more than 100 males" "Attracted by the strong scent emitted by the females, the snakes become embroiled in a sexual frenzy" "The confusing massive bodies provides the opportunity for some males to cheat" "They emit a scent identical to that of a female and so draw other males away from the real females" "As a result they can increase their chances of mating by as much as the third" "Females are keen to leave the dens and feed on the open prairies but heavily outnumbered they are often overpowered" "Whatever the tactics of the males, the females will mate only once" "For garter snakes, their annual sexual marathon is drawing to a close" "With the long days of summer in full-swing across the northern hemisphere one particular seabird ventures northwards from Africa and southern Europe" "And there is one place it favors - Bass Rock, off Scotland's east coast" "Gannets arrive in Britain from January onwards, but their numbers build throughout the spring" "For most of these birds this is familiar territory, they would have made the same journey every year" "Breeding couples are not only loyal to Bass Rock but to each other and the gentle bout of bill fencing is their way of saying so" "The number of gannets gathering on this tiny island has grown 5 fold in 30 years by May, 70,000 birds cram tightly together making this one of the largest gannet colonies in the world" "It's little surprise therefore that some gannets have trouble locating the right nest" "A male gannet establishes his nesting territory when he is 3 or 4 years old" "From then onwards he and his partner will use the same nest site each year" "A gannet nest is hardly an architectural wonder, but home improvements will continue throughout the summer" "Gannet chicks eat only a few times a day, but when they do, it's quite a feast" "Their main diet is a mix bag of herring, mackerel and sand eels, served up with a dash of saliva" "Keeping the feathers in good condition is an important routine for every bird and gannets look after theirs with exquisite precision" "Both male and female gannets go fishing and to ensure that a chick isn't left alone one parent signals its intention to leave by pointing its bill skywards" "Air traffic around Bass Rock reaches a peak as mid summer approaches" "A diving gannet can hit the sea surface at a staggering 100km an hour slicing through the water with a torpedolike velocity" "The north sea provides rich rewards for these birds and their fishing trips can last between 7 and 13 hours, a direct benefit of the long summer days as they peak towards the summer solstice" "In high summer, America's northernmost state stages a double spectacle" "For salmon it's the once in their lifetime chance to breed" "For grizzly bears, it's an unmissable midsummer feast" "It takes a special event for the normally solitary and antisocial grizzlies to tolerate such a large gathering" "And while there would always be the one that gets away" "In a good year, a grizzly can eat some 30 kilos of salmon in a day" "In poor salmon years, males will dominate the main fishing grounds, females and cubs have to be content to fish on rivers away from the bigger males" "Cubs born early in the summer discover how to fish by watching their mother" "This yeanling has already learned to be more bold" "Grizzly mothers don't feed their young directly, it's a case of grab what you can" "Losing some food to an offspring is one thing, but the smell of a fresh catch can attract bigger competition" "Summertime it's better for a mother and her cubs to hang out in the relative safety of some tall grass staying close to mom is an inbuilt mechanism for survival" "Even so, fewer than half the cubs will make it to adulthood" "Grizzlies are largely vegetarian, with less than a 3rd of their diet to be meat" "Despite their baby teeth, spring cubs take to grazing early on" "During summer, McNeil River Falls sees the biggest gathering of grizzlies in the world and for bears that usually have home ranges of hundreds of square kilometers getting on with the neighbors can be difficult" "The common hunger that draws some of the biggest of America's brown bears together could also produce some of the biggest fights" "But they are for the most part tolerant of one another, spending much of the day practising their varied styles of fishing" "The basics are taught to the cubs by their mothers, but as they get older, bears improve on these skills becoming more adept at catching fish with a minimum amount of effort" "Large males weigh between 3 and 500k, the weight of 6 fully grown men" "They can eat up to 15% of their body weight in a day but if the runs are good, they become more selective often eating just the eggs" "In a poorer salmon year, every bit is savored but not always by the bears" "With their powerful front paws, keen vision and a good sense of smell, some grizzlies become very expert indeed" "But keeping a catch isn't always easy" "Being in close company with other bears is certainly stressful but the rewards it brings are great and the bears need all the food they can get to carry them through their long and lonely winter hibernation" "These river bears will stay together throughout the long days of summer" "The Rift Valley lakes of east Africa are home to some 3 million lesser flamingos" "It's the biggest gathering of any inland water bird in the world and it's a wonder that can be seen throughout the year for here on the equator, conditions are fairly constant" "The volcanic forces that shape the landscape are never far away" "Hot springs bubble constantly giving the birds their very own steam bath" "The hot corrosive water at this caustic soda lake deters most animals so flamingos have almost exclusive access to the microscopic blue-green algae it contains" "They spend much of the time with their heads upside down filtering the algae from the distasteful water" "Special airchambers in the bill provide extra buoyancy so that they only sift the upper surface where the algae is most abundant" "The water in the lake is too toxic to drink, so every day the flamingos fly off to find something a little more palatable" "The volcanic springs that feed the lake may not be the sweetest of the waters but they are not caustic" "With so many birds wanting to quench their thirst, flamingos have to queue politely and wait their turn" "They also have a much-needed opportunity to take a bath and wash away the lake salts that coat their feathers" "Flamingos are the most vulnerable when they are close to the lake edge" "A fish eagle can only catch one if it's in shallow water so many birds packed so closely together could easily panic and exploiting that is the eagle's favorite technique" "At times, the whole colony will join together to perform a ritualized dance which may help them to synchronize their breeding" "At the other end of the world, conditions couldn't be more extreme" "While the northern hemisphere enjoys long summer days, a winter blackout has descended across this frozen southern continent the occasional burst of the aurora provides the only light" "The winter temperatures have been dropping as low as minus 60 degree Celsius and thousands of male emperor penguins have spent the last two months huddled together in one great scrum" "The first sign of seasonal change is the reappearance of the sun, a distant blip on the horizon" "It seems perverse of these birds to decide that winter in Antarctic is the best time to bring up their young" "The females are away fishing and most of these males are carrying eggs on the top of their feet beneath a special fold of feathered skin" "In ferocious winds of 200km/h the only practical way for them to keep warm is by huddling" "It's a very democratic system, the penguins constantly move round the edge of the colony ensuring that each gets a reasonable time in the lee of the huddle away from the wind" "By August, the warmer temperatures allow the colony to break up" "Winter has taken its toll and the males have lost half their body weight" "They're also left holding the baby" "These newly hatched chicks can expert very little from their fathers" "After four months of fasting, there is nothing solid in a male's stomach but he is able to produce a protein rich secretion but that is barely enough to keep a chick alive for a week" "Fattened up from 2 months' fishing the females reappear with magically accurate timing" "In such a crowd, calling is the best way to locate her partner" "A female arrives to take over at first, the male is a little reluctant to abandon his offspring" "Once the exchange starts, it needs to be quick a few minutes on the ice would almost certainly kill the chick" "Now at last, the chick can feed properly" "During the next 5 months, an emperor chick would eat 100k of food" "In one big helping, it can eat 1/3 of its own body weight" "Now at last, their fathers have a chance to eat but the ice edge may be several hundred kilometers away" "Emperor penguins have a fast mode of transport than just plain walking, they can toboggan" "From now on, males and females will take turns to go fishing" "Each trip may involve travelling thousands of kilometers in search of food" "With spring now well established in the southern hemisphere one of the world's smaller dolphins makes an entrance" "Dusky dolphins live permanently around the coasts of New Zealand but at this time of year, they gather off the south island in pods hundred strong" "And being a dusky dolphin requires a certain acrobatic flair" "Why these dolphins leap is still uncertain, but males are known to chase females in an airborne courtship and spring is the beginning of the mating season" "Leaping may also be a technique used by the pods to herd fish" "The splashes of the dolphins at the front of the pod could well signal to others the location of fish and may push their prey towards the dolphins in the middle" "Whatever the reason, duskies are without doubt highly cooperative and social animals" "Some of the big pods number 500 and reach their peak during the southern hemisphere's spring and summer" "Gathering in such numbers, seems to stimulate the dolphins to perform their most dazzling acrobatics" "Still in the southern hemisphere just south of the equator, one of nature's greatest shows is taking place" "Nearly 2 million wildebeest, this journey is the biggest land mammal migration on our planet" "They're driven to cross every obstacle and the Mara river is the most perilous" "It's the promise of rain that starts them on their cyclical journey and wildebeest noses can detect rainfall 30km away" "The sight and smell of the Mara river seems to panic the wildebeest and the resulting crush becomes more hazardous" "Wildebeest like many grazing animals find safety in numbers but big numbers nonetheless attract attention" "This is one of the few occasions when crocodiles work as a team" "It can sometimes take more than one pair of jaws to overpower a wildebeest" "A river crossing may last several days and the vast majority of wildebeest will make it successful" "Inevitably though some will be luckier than others" "And this is why they do it the shifting rains have brought fresh growth to the pastures of the Serengeti the new grass will support the herds for the next 6 months then once again, new rains in the north will bring them back full circle" "Across the Indian Ocean, and almost on the same latitude as the Serengeti" "Christmas Island has now experienced the first rains of its monsoon" "The humid conditions are a trigger for the emergence of this island's most common resident, the red crab" "November is the start of a mass migration for these land crabs" "The males leave their burrows first and within a few days there are spectacular numbers of them out in the open" "This is just the first wave of a migration that will ultimately involve some 80 million crabs" "Soon they spill out of the forests into human territory" "Road traffic is one of their biggest hazards" "The crabs follow migratory paths that run in almost straight lines and they take no account of oncoming traffic" "Their destination is the sea and after a couple of weeks travelling, the male crabs head straight for the water" "Red crabs lost their sea legs long ago in evolution and so now they are in danger of drowning the water in a rock pool is the safest way of getting a drink" "Salts lost on the journey are recovered by a quick dabble in the surf" "Soon after they arrive, the male crabs leave the beach and make new burrows in the forest above the coast" "With the arrival of the females the whole reason for their journey becomes apparent" "Red crabs may live on land, but their reproduction is tied to the sea" "Once mated, the female takes over the burrow and remains there for two weeks incubating her eggs in a specialized pouch" "When she emerges, she joins other females each carrying around 100,000 eggs" "This final stage of the journey from the coastal forest to the sea is the equivalent in human term of a person carrying a 7-kilo-load for over 30km" "From the outset the red crab migration is operated with military precision" "It culminates in millions of expectant mothers reaching the sea on the eve of the highest tide" "While some crabs will attempt to release their eggs from the cliffs, most take the final few steps to the sea edge" "For some, this is their first time but for others, it's a familiar experience" "Red crabs can live for as long as 20 years" "This is a dangerous time for them since they are poor swimmers many will drown but the urge to release their eggs is overwhelming" "Each wave surging up the beach, stimulates the crabs to release their eggs and the retreating water turns brown" "Hopping up and down helps empty the egg pouches" "The young hatchlings will remain in the sea for 3 weeks and then return to land but only a tiny fraction will survive to do so" "Another generation is spawned ensuring that Christmas Island will remain the island of red crabs" "The last stage of our global journey takes us to the Great Barrier Reef the first structure built by living organisms to be identified from space" "It stretches over 2000km and is home to 400 different types of coral" "It's the largest living structure in the world" "But the real magic of this spectacle isn't in the size of the reef or the numbers of the animals it supports" "Now in mid-December the summer solstice is approaching in southern hemisphere for each and every coral their one chance to reproduce is about to arrive" "Water temperature and the lunar cycle act as triggers" "For several days after a full moon, the corals synchronize the release of their eggs and sperm into the ocean" "Individual corals of the same species spawn together, their timing is precise to the hour" "The full secrets of the reef's spectacular sex life were not discovered until 12 years ago a reminder that we still have much to learn about our planet" "As the spawning reaches its climax, billions of eggs and sperm are cast adrift it's as if nature is throwing its own firework party" "Great mass spectacles are rare in nature many are ephemeral lasting only a matter of days or weeks" "Today we are perhaps more aware of their fragility the last Millennium may have been an age of discovery but it was also one of loss" "200 years ago, the wilderness of north America was home to a sight that stunned the pioneering settlers" "60 million bison roamed the vast expanses of the American prairies" "They must have seen so numerous as to be indestructible, but within less than a century, their numbers were reduced to just 600" "We may have lost the spectacle, but we still have the species" "I'm in the first of all national parks Yellowstone in the United States and here carefully protected a handful of bison have increased to several thousand" "It's true that in the past century we've been inflicted terrible damage on the earth but thanks to the work of conservationists, there is still a great deal to celebrate on this planet long may remain, so Happy New Millennium"