The Russian Arctic is one of the world’s most extreme habitats, yet it is a haven for polar bears, lemmings, arctic foxes and walruses. In late August, massive muskoxen bulls gather together to compete for mating dominance. Each bull can weigh 400 kilogrammes and charge at a speed of 40 kilometres an hour; a head-to-head impact can be heard more than a kilometre away.

• Christian Brückner