Migrating to New Zealand around 1250–1300, Polynesians brought kiore (the Pacific rat), which wiped out some smaller species of bird, as well as frogs and lizards.
Europeans came from the late 18th century, bringing Norway rats and ship rats, cats, stoats, weasels and ferrets. Like the kiore, these predators could reproduce rapidly and disperse widely. They vacuumed up the smaller prey (and continue to do so), starting with whatever was easiest to catch – frogs, lizards, invertebrates and small ground-nesting birds. But the new arrivals could also kill larger prey, and some were good climbers and not so afraid of water. This meant that species that had survived attack by kiore were now at risk.
Humans hunted large, conspicuous prey – seals, moa and other large birds – as long as they could be found. This resulted in the first human-caused extinctions of New Zealand species.
Why so many bird extinctions?
New Zealand birds evolved in isolation over millions of years. Unlike elsewhere, there were no land mammals such as bears, badgers, lions or goats. Free from attack and competition from mammals, many birds became ground-dwellers. They were therefore natural prey for humans and the predators they brought, and vulnerable to land clearance.
Discovering extinct birds
In New Zealand, European settlers noticed the evidence for the extinction of the megafauna – moa and other large birds – from around the late 1830s. Moa bones belonging to a number of moa species were found in middens (ancient rubbish sites), swamps and caves. The remains of other species, including large extinct geese, adzebills, and the giant Haast’s eagle, were also discovered before the end of the 19th century.
Just how many smaller birds had become extinct was not realised until after 1990, when the food remains of the extinct laughing owl were discovered and analysed. Beneath the owl’s former roosts in sheltered caves were layers of bones of their prey, piled up over centuries. These bones were evidence of the former abundance of birds such as saddlebacks, now killed off on the mainland, and surviving only on predator-free islands.
Returned to the soil
At some southern South Island archaeological sites where moa bones were found in the 19th century, the bones were so abundant that they were carted away and ground up for fertiliser.
Loss of creatures large and small
The extinctions in New Zealand have been unusual because small species died out at the same time as the megafauna (large birds in this case). Now most of the large species are gone, and small birds continue to be threatened and lost. Indeed, the New Zealand extinctions have aspects of both the continental extinctions (involving mainly large species), and of island extinctions (where small species were the main casualties).
Over a period of 750 years New Zealand’s vertebrate fauna has been nearly halved, and there have been uncounted losses of populations and species of invertebrates.
The list of New Zealand species known to have become extinct since human settlement includes one bat, at least 51 birds, three frogs, three lizards, one freshwater fish, four plant species, and a number of invertebrates. Of these, 21 bird species, the bat, fish and two lizards survived 500 years of human and kiore predation. Although often severely depleted they appeared in European drawings, written records and museum collections. But as new, effective predators arrived, they slipped into extinction.
Back from the dead
So-called zombie species – those which might otherwise be extinct – have survived because humans protect them from introduced predators. They include species that no longer have natural populations (such as the kākāpō), and those maintained in captivity or in part of their original range (such as the South Island takahē).
Plants and fungi have not escaped – several are extinct, and over 100 plant species are classified as critical or endangered. Some birds are still declining: the bush wren, South Island snipe and South Island kōkako were last seen alive in the 1960s.
Remnant bird populations
Other bird species have been drastically reduced. The South Island takahē was once widespread in places such as North Canterbury’s plains and foothills. Loss of habitat, along with hunting, reduced it to a tiny remnant in Fiordland. The only North Island takahē seen by Europeans was carried down from the Ruahine or Tararua ranges in 1894. More seabird than land bird species have survived, as many were on offshore islands.