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Christmas Island heroes
Robber crabs were lured away with food to protect them during the baiting program.
October 2009
The hard work of the Christmas Island Yellow Crazy Ant Team is paying off - ant count data indicates numbers have declined by over 99 per cent within four weeks of baiting.
After six months of hard, physical work, aerial baiting to deliver low concentration ant bait to all known crazy ant supercolonies began last month.
The project started with the field crew traversing the entire 135 square kilometre island to survey ant density at over 900 waypoints. The team located 57 separate supercolonies. Each supercolony was then precisely mapped on foot, despite the incredibly rugged terrain.
These maps were used by the helicopter pilot to accurately deliver bait to the ant colonies. The team also conducted extensive surveys for non-target impacts of the heli-baiting.
Robber crab lures worked brilliantly to help minimise robber crab mortality. Amazingly, not a single red crab has been found killed by the baiting campaign.
Red crab annual breeding migration
Crab crossing grids have been built to help the crabs safely cross roads.
Plastic walls help funnel crabs to the crossings.
October and November 2009
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 and release eggs into the sea.
Breeding is usually synchronized island wide. The rains provide moist overcast conditions for crabs to make their long and difficult journey to the sea. The timing of the migration breeding sequence is also linked to the phases of the moon, so that eggs may be released by the female red crabs into the sea precisely at the turn of the high tide during the last quarter of the moon.
It is thought that this occurs at this time because there is the least difference between high and low tides. 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.
The main migration commences on the plateau and can last up to 18 days. Masses of crabs gather into broad columns as they move toward the coast, climbing down high inland cliff faces, and over or around all obstacles in their way, following routes used year after year for both downward and return migrations.
Movement peaks in the early morning and late afternoons when it is cooler and there is more shade. If caught in open areas, in unshaded heat, the crabs soon lose body water and die.
Read more about Christmas Island's red crabs | Images for media