Isabela's rich bird, animal and marine life is beyond compare. Isabela is home to more wild tortoises than all the other islands. Isabela's large size and notable topography created barriers for the slow-moving tortoises; apparently the creatures were unable to cross lava flows and other obstacles, causing several different sub-species of tortoise to develop. Today, tortoises roam free in the calderas of Alcedo, Wolf, Cerro Azul, Darwin, and Sierra Negra.