 Population decline accelerated with the early settlement of the islands in the early 19th century , leading to unregulated hunting for meat , habitat clearance for agriculture , and the introduction of alien mammal species . Feral pigs , dogs , cats , and black rats have become predators of eggs and young tortoises , whilst goats , donkeys , and cattle compete for grazing and trample nest sites . The extinction of the Floreana subspecies in the mid @-@ 19th century has been attributed to the combined pressures of hunting for the penal colony on the relatively small island , the conversion of the grazing highlands into land for farming and fruit plantations , and the introduction of feral mammals . 
