Monday, January 10, 2011
January 10, 2011 : Christmas Island Migration
Christmas Island Migration
At the beginning of the wet season (usually October / November), most adult red crabs suddenly begin a spectacular migration from the forest to the coast to breed. Breeding is usually synchronized island-wide. The rains provide moist overcast conditions for crabs to make their long and difficult journey to the sea.
During peak migration times, sections of roads where crabs cross in high numbers may be closed to vehicles for short periods of time. You can park your vehicle and carefully walk amongst the moving sea of crabs as they relentlessly make their way to and from the shore.
While the rains provide the moist preconditions for the march to begin, the timing of the migration breeding sequence is also linked to the phases of the moon. Eggs are released by the female red crabs into the sea precisely at the turn of the high tide during the last lunar quarter.
The sea level at the base of the cliffs and on the beaches, where the females release their eggs, at this time varies the least for a longer period, and it is therefore safer for the females approaching the water's edge to release their eggs. Sometimes there are earlier and later migrations of smaller numbers of crabs but all migrations retain this same lunar rhythm.
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