November 28, 2012
Scientists Study Galapagos Tortoise Migration Patterns
Lee Rannals for redOrbit.com - Your Universe Online
Scientists using GPS technology and modern 3D acceleration measurements have mapped out the annual migration of the Galapagos giant tortoise.
The team from the Max Planck Institute for Ornithology found that the male tortoise can travel up to 6.2 miles into the highlands of the island, and they usually start their annual migration at the beginning of the dry season.
According to the findings, only the full grown animals migrate, while the young tortoises stay year round in the lowlands.
The Galapagos giant tortoises helped to contribute to Charles Darwin's theory of evolution when he noticed the differences between the populations of the tortoises.
In order to study the migratory pattern of the tortoises, the team secured GPS loggers with 3D acceleration monitors onto 17 adult tortoises. This technique allowed the scientists to determine the animals' exact position and behavior over a period of two years.
The scientists gathered information on the entire population by noting the size, sex and location of each tortoise they met on their monthly hikes along the volcanic hillsides. They combined the GPS data with the temperature data and information about the availability of vegetation.
The scientists found that the tortoises have a partial migration system, where not every individual migrates.
In June, the tortoises start their slow, 6.2-mile hike into the highlands, while adult females remain in the lowlands until they lay their eggs. After eggs are laid, the females then begin their trek, while the smaller tortoises stay in the lower elevated areas year round.
The study also found that the giant tortoises wander for large distances in search of food, even though the animals can survive for up to a year without eating.
Scientists are still unsure why the younger animals do not make the migration trip to the highlands.
“Either the energy expenditure of this strenuous hike is too high, or there is still enough food available for the smaller animals.” said Stephen Blake, a researcher in the study. “Perhaps the younger animals can´t tolerate the wet cold climate of the higher regions.”
The largest and dominant individuals of other species of animal do not migrate because they are able to defend themselves against competitors. With the Galapagos tortoises, the largest and dominant individuals are the ones that take the journey.
Future studies could show how environment influences the migration scheme of these turtles. During these studies, scientists want to include factors like age, size, sex and morphology to see why the behavior changes in different lifetime stages.
The scientists said the Galapagos tortoise still shows its original migrating behavior, despite invasive species like goats and rats.