From the northern tundra to the southern swamps, wildlife here has to cope with intense seasonal change and extreme weather events.
The third largest continent is North America. It occupies about 16.5 per cent of the world’s landmass and, like Asia, it extends from the Arctic to the tropics. The big difference is its especially extreme weather, which is all down to its geography.
In Asia, the major mountain chains run in an east–west direction, but in North America, the Rockies and Appalachians are aligned north–south. In between are the vast grasslands of the Great Plains and a complex of very different wildlife habitats, from steppe in the north and hot deserts in the southwest to swamps and bayous in the south and southeast. It means that, with nothing to impede it, cold polar air can barrel down towards the Gulf of Mexico, where it meets warm air from the tropics.
The result is tornadoes.
The USA experiences up to 1,717 major tornadoes a year: more than anywhere else in the world. And, if that’s not enough, the southern and southeastern parts of North America, including the Caribbean, are regularly slammed by particularly powerful hurricanes that swing in from the tropical Atlantic.
The regular occurrence of these extreme weather systems makes the continent unique.
On the coast to the west of the Rockies, the Pacific Ocean ensures that the climate is mild and damp, both summer and winter. There are no extremes here. As a result, it supports the largest tracts of temperate rainforest in the world. They stretch from southern Alaska to northern California, where they are home to the American black bear and, on Canada’s Vancouver Island,
a subspecies that is slightly larger and darker than its mainland relatives. The Seven Worlds North America filming team visited the island in search of a mother and her cubs, and discovered that the family regularly went beachcombing. Wildlife cameraman and drone operator Bertie Gregory was with the team.
“One of the best parts of filming on these big landmark series is the amount of time you get to spend with the animals, especially if you get to follow known individuals. I had managed to find a female bear with two small cubs, so we spent about four weeks following their daily routine,” recalls Bertie.
“We filmed them mainly at low tide each day, when they came out of the forest and began to forage on the beach. At low water, the sea retreats from the many inlets along the coast, revealing vast boulder fields.
Under the rocks is a veritable smorgasbord ready to satisfy a hungry bear. The mother would sniff amongst the boulders until she smelled a crab, then she’d flip over the rock and grab the food before it nipped her nose. The amazing thing was that the boulders were very heavy, yet she turned them over with just the deft movement of her paw. The cubs, which were super cute, learned from their mother, and while we were there we saw how they progressed from flipping over pebbles to tackling quite large stones. With all that weightlifting from an early age, it’s no wonder that adult bears are so strong!”
Streaming with life
Moving rocks about came to be a bit of a theme in the North America episode, with director Sarah Whalley heading for the rivers of the Southern Appalachians to find a fish – the river chub – that
builds huge mounds of pebbles in order to impress females.
“The first time I donned a wetsuit and snorkel and put my head under, I was blown away. The colourful life in front of me was as striking as that on a coral reef. It’s such a vibrant, but little-known world. People would stop and ask us what we were filming (well we did look odd floating face down in the river!) and, when we showed them, they couldn’t believe what was in their own backyard. This area is a hotspot for aquatic life. There are more species of freshwater fish, crayfish and salamanders in these waters than anywhere else in the temperate parts of the world.
“The river chub is actually quite a common fish in North America, but the lengths to which he goes to build his mound is extraordinary.
Once a male got going, there was no stopping him. He’d collect and place one pebble after another, all the while watching for females, until he had a pyramid-shaped mound about a metre across. There were times when he would place a stone and it would roll off, but he immediately put it back in its rightful place.
One day, we watched as a male built a nest, then deconstructed it, and rebuilt it a half-a-metre away – they really can be quite particular.
“Unfortunately, the chub’s delicate ecosystem is under threat from human encroachment. It was brought home to us every day. Our cameramen would lift their heads out of the water and hear gun shots from the nearby shooting range.”
“The first time I put my head under, I was blown away. The colourful life in front of me was as striking as that on a coral reef.”
A female polar bear leads her two cubs through a patch of colourful fireweed. During summer, with no sea-ice to hunt on, polar bears in this area are restricted to the shores of Hudson Bay, Canada.
A beachcombing black bear teaches her cub to leave no stone unturned. In South Dakota a female prairie dog watches over her pups. A roadrunner perches on a stump to get a better view of his territory in the Sonora desert.
Total land area: 24.71 million km² Human population: 427 million Population density: 24 per km² Number of countries: 23 (+ 9 dependencies) Country with the most threatened species: United States, 1,818* Conservation threats: habitat destruction, degradation and fragmentation, invasive alien species, diseases, over-hunting, pollution and climate change Every autumn the waters off the coast of Florida turn dark with the migration of millions of grey mullet. They hug the shallows for safety. 5 The male river chubb creates a nest out of rocks. Smaller fish such as bright orange ‘shiners’ crowd in to lay their eggs in his impressive stone pile. THE STATS *Includes IUCN Red List categories: Critically Endangered, Endangered and Vulnerable.