From October each year, approximately 10 million straw-coloured fruit bats arrive at Kasanka National Park in what is the globe’s most significant mammal migration. They roost by day in a small patch of swamp forest, leave at sunset in a stream that takes an age to pass overhead, and return before dawn.

It is an amazing sight, and a short one — the colony is concentrated into a few weeks, which makes timing a visit the whole of the planning. Hides are set up to watch the evening departure and the morning return, and the park is otherwise quiet enough that the spectacle feels entirely uncrowded.