Every year tens of millions of red crabs on Christmas Island in Australia migrate from the forest to the coastline. It is one of the largest known animal migrations in the world. It begins with the first rainfall in the wet season, which started last week.
The staff of Christmas Island National Park spent months preparing for the migration. They erected temporary barriers along roadsides to funnel the crabs toward specially-constructed crab bridges, which allowed them to safely travel over roads.
Although there is not much traffic on Christmas Island (their population is just 1,400 people), the sheer number of crabs would halt what traffic there is completely. The crabs travel right through the township before eventually arriving at the coast. Each female crab will lay up to 100,000 eggs into the Indian ocean. The speed of the migration is determined by the phase of the moon and rainfall! The spawning event for 2021 is expected to take place on the 29th and 30th of November before dawn each day, when there is a receding high-tide during the last quarter of the moon.
David Attenborough and red crabs
David Attenborough documents the red crab spawning process on Christmas island and explains how they travel across the island.