November 28, 2012 1:56 pm
Birds do it, butterflies do it, and now, we know that Galapagos giant tortoises do it, too. Migration extends to animals around the world, but why the tortoises bother with this behavior remains a mystery. We do know, however, that only fully grown animals—most often the dominant males—migrate around 6 miles each dry season into their native island’s volcanic highlands.
In the cool dry season, the island’s highlands are engulfed with fog, which favors plant growth while vegetation in the lowlands tends to shrivel up in the absence of rain. During the rainy season, however, plants in the lowlands are more succulent and nutritious. Not every tortoise follows the flow of available food, however. Scientists outfitted 17 adult tortoises with GPS loggers and acceleration monitors to see where the animals chose to spend their time. Adult males take off in June while females tend to remain in the lowlands until they lay their eggs. Smaller tortoises stick around the lowlands all year round.
The giant tortoises can survive a full year without nourishment, so why do they bother making this energetically demanding hike at all? In other species, the largest and most dominante individuals usually skip migration because they can handle any competition that remains behind. Why the tortoises display the opposite trend remains a mystery, at least for now.
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