Tens of millions of red crabs on Christmas Island are on the move from the forest to the coastline in one of the world’s great wildlife migrations.

Christmas Island National Park staff spend months preparing for the migration each year erecting temporary barriers along roadsides to funnel crabs toward specially constructed crab bridges.

Christmas Island National Park acting manager Bianca Priest said this spectacular natural event took place on Christmas Island every year.

“Christmas Island National Park staff put up kilometres of temporary barriers, erect signs and close roads across the island to protect millions of crabs leaving their forest homes for the coast. Together, with the ongoing support of the Australian Federal Police, Shire of Christmas Island and the community, these efforts help protect the island’s keystone species,” Ms Priest said.

“World-renowned naturalist Sir David Attenborough described the red crab migration as ‘like a great scarlet curtain moving down the cliffs and rocks towards the sea’ and considered filming the spectacle as one of his 10 greatest TV moments.

“Over the years visitors have travelled from every corner of the world to witness this wildlife phenomenon.”

The annual red crab migration is an extraordinary natural process triggered by celestial, tidal and meteorological forces.

It begins with the first rainfall of the wet season with the speed of the migration determined by the phase of the moon. Red crabs always spawn before dawn on a receding high-tide during the last quarter of the moon.

With the first rains arriving last week the crabs began their journey with huge numbers of crabs moving from the forest to the sea over the cliffs and through the township.

This year the spawning event is expected to take place on the 29-30 November 2021. It is then that each female red crab will release up to 100,000 eggs into the Indian Ocean.

Baby red crabs may return to the shore about one month later to make their journey back into the tropical forest of Christmas Island.