What is migration?
When most people think of migration, they only think of birds migrating south for the winter. There are however, tons of different species that take part in migration events. Animal migration occurs when individual animals move a relatively long distance, usually on a seasonal basis. Many different species take part in migration including birds, mammals, fish, reptiles, amphibians, insects, and crustaceans. There are multiple environmental factors that can trigger the migration. Some of these include the local climate, the availability of food, what season it is, or mating reasons. To be considered a “true migration”, and not just a local dispersal or irruption, the movement of the animals should occur annually or seasonally. Examples of this include birds migrating South from the Northern Hemisphere for the winter, or wildebeest migrating annually for seasonal grazing.
Migration is an adaptive response to certain seasonal or geographic variations of resources. The change in seasons provides a drastic difference in the duration and intensity of solar energy received in each hemisphere. It also allows the animals that migrate to take advantage of favorable food and weather conditions in the different locations. Animals can travel hundreds to thousands of miles during migrations.
How do the animals know where to go?
Migration of Red Crabs
The Christmas Island Red Crab is a species of land crab that is native to Christmas Island and the Cocos (Keeling) Islands, which are located in the Indian Ocean. Red is the most common color for Christmas Island Red Crabs, although they can also be found in orange, and very rarely purple. They are a larger species of crab, with an adult crabs body shell measuring up to 116mm across. Their body shell encloses their lungs and gills. The claws of these crabs are usually equal in size and they have the ability to regrow missing claws.
There were an estimated 43.7 million adult red crabs on Christmas Island alone, but this number dropped drastically after the yellow crazy ant was accidentally introduced. It is believed that these ants have killed between 10–15 million crabs. Christmas Island red crabs are most known for their annual mass migration to the sea. They migrate here so that they are able to lay their eggs in the ocean. The crabs only migrate during the rainy season, and if there is not enough rain, they will halt their migration.
The video below shows some great footage of the migration and explains a little more about it.