 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 species 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.Scientific collection expeditions took 661 tortoises between 1888 and 1930, and more than 120 tortoises have been taken by poachers since 1990.