A view of Singapore skyline from Marina Bay Sands.
Monarch butterflies, Mexico
In one of the most sensational migrations on Earth, around 250 million monarch butterflies travel south from America every November to the Oyamel fir forests of Mexico, where they fill the sky with a storm of orange and black. So dense are their numbers that tree branches sag under their weight. Three main bio-reserves exist to support the butterflies: El Rosario, El Capulin and Piedra Herrada.