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Program Great Migrations

  • 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.

    Video 1: First, the male crabs meet the females on the shore. The males dig dens near the shore for the females to brood, or hatch, their eggs. Once they've mated, the males return to the forest and the females retreat to their dens.

    Video 2: After 12 or 13 days of brooding their eggs, and with the arrival of the waning moon, female red crabs make a journey to the sea. Females reach the shore and release their eggs in the water. The waning moon plays a critical role in this stage of migration. The angle of the moon creates a neap tide, resulting in tides that are milder than usual. This gives the offspring a greater chance of survival.

    Video 3: When released, the eggs hatch almost instantly, but the larvae remain in the water for one month, growing through several larval stages. Few are able to survive the harsh ocean currents and marine predators. Those that do survive begin the journey back into the rain forest, battling predators such as the yellow crazy ants along the way.

  • Term Part of Speech Definition Encyclopedic Entry
    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.

    Australia Noun

    continent and nation between the South Pacific and Indian oceans.

    burrow Noun

    small hole or tunnel used for shelter.

    crab Noun

    type of marine animal (crustacean) with a flat body, hard shell, and pincers.

    crevice Noun

    crack in a rock.

    Indian Ocean Noun

    one of Earth's four oceans, bordered by Africa, Asia, Australia, and Antarctica.

    larva Noun

    a new or immature insect or other type of invertebrate.

    lunar cycle Noun

    complete cycle of visible phases of the moon, approximately 29.5 days.

    migration Noun

    movement of a group of people or animals from one place to another.

    neap tide Noun

    the lowest level of high tide when the difference between low and high tide is the least, occurring when the gravitational pull of the sun counteracts that of the moon.

    plateau Noun

    large region that is higher than the surrounding area and relatively flat.

    Encyclopedic Entry: plateau
    predator Noun

    animal that hunts other animals for food.

    rain forest Noun

    area of tall evergreen trees and a high amount of rainfall.

    tide Noun

    rise and fall of the ocean's waters, caused by the gravitational pull of the moon and sun.

    Encyclopedic Entry: tide
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