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Program
Red crabs are native to Christmas Island, Australia. The central plateau of Christmas Island is dominated by strands of rain forest. The island has a tropical climate and experiences both a wet season (December through April) and a dry season (May through November).
More than 120 million red crabs can be found on the rain forest floor of Christmas Island. Red crabs live alone in dirt burrows, or deep rock crevices. Crabs stay in the shade of their dwelling for most of the year. In October or November, when the wet season is about to return, crabs begin their migration to the shore. This timing coincides with the lunar cycle and the tides.
This video documents the second stage of the red crab migration, after the crabs have mated and before the eggs hatch in the ocean. At the start of this stage, females brood their eggs in dirt or coastal rock burrows for 12 to 13 days. A female red crab can lay up to 100,000 eggs, which she holds in her abdominal sac. With the arrival of the waning moon, females make their way into the sea. In what looks like a dance, females brace themselves at the waters edge, and release their eggs.
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How many eggs can a female crab produce?
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Answer
A female crab can produce up to 100,000 eggs.
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Answer
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How many days does the female red crab sit with her eggs?
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The female red crab sits on and protects her eggs for 12-13 days.
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Answer
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What cues the red crabs to lay their eggs and begin migration?
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Answer
The waning moon cues the red crabs to lay their eggs. A waning moon means that the moon is decreasing in size, moving from a full moon towards a new moon. During this time, the moon takes on a crescent shape.
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Answer
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What kind of tide is best for the female crabs to release their eggs?
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Answer
Red crabs release their eggs during mild or low tides, coinciding with the waning moon. Although the tide is low, many female crabs drown as they attempt to release their eggs into the sea.
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Do most of the eggs survive to return as hatchlings?
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No, only a handful of the hatched eggs survive and return to shore.
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animal migration
Noun
process where a community of animals leaves a habitat for part of the year or part of their lives, and moves to habitats that are more hospitable.
burrow
Noun
small hole or tunnel used for shelter.
crab
Noun
type of marine animal (crustacean) with a flat body, hard shell, and pincers.
lunar cycle
Noun
complete cycle of visible phases of the moon, approximately 29.5 days.
offspring
Noun
the children of a person or animal.
Noun
rise and fall of the ocean's waters, caused by the gravitational pull of the moon and sun.
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