Populations of species on islands tend to be small so they are vulnerable to extinction. The ways that humans cause extinctions are shown clearly on islands like New Zealand and Madagascar. After first contact with humans, many island species disappear due to hunting, habitat alteration or the effects of introduced predators or competitors.
Extinctions in New Zealand
The ancestors of the modern Maori people of New Zealand colonized the island in the 13th century. They cleared about 40 percent of forests using fire, introduced rats and dogs and hunted the moas to extinctions.
The kakapo, a flightless parrot, and the tuatara, a primitive, lizard-like reptile, are endangered species that cling to existence on only a few offshore islands. In 2001, the kakapo had a population size of just 62 birds spread over three small islands. This species is a nocturnal ground nester, and it is threatened by extinction due to predation by introduced mammals like rats, cats and dogs.
Tuataras are also nocturnal and nest in burrows. Fossils show that they were widespread in New Zealand before human colonization but they are now found only on offshore islands. The tuatara is not as threatened as the kakapo, but it suffers from predation by rats, particularly on eggs and young. Conservation programs that eradicate rats from islands have increased tuatara populations.
Moas were large, flightless birds that weighed up to 500 pounds. Eleven species have been identified from fossil remains. They were herbivores, and coprolites (fossil moa dung) show that they ate herbs and shrubs. Bones at archeological sites indicate that the first human colonists hunted moas for food, and they may have killed them off in just a few decades.