Few land bird species
Only 91 of New Zealand’s 252 native birds are land birds. (These numbers include recently extinct species.) The rest are wetland birds, shore birds or seabirds. This is unusual, as 90% of the world’s birds are land birds.
Part of the reason for New Zealand having a smaller proportion of land species is the country’s extensive wetlands, long shoreline, and vast marine area – ideal habitats for birds of shore and sea. But another factor is that 2,000 kilometres of water separate modern-day New Zealand from its nearest large neighbour. Land birds are less likely to fly long distances across water than the other groups.
New Zealand’s passerines
About half the world’s bird species belong to one order, Passeriformes. These are passerines (sometimes called the perching birds), and include sparrows and blackbirds. New Zealand has 49 native passerine species, with nine found only on outer islands.
Native passerines include some of the world’s oldest – the rifleman and rock wren (Acanthisittidae family), and the wattlebirds (Callaeidae family). Other passerines include the whitehead (Mohoua albicilla), robins (Petroica species), the tūī, and the recently extinct piopio (Turnagra capensis and T. tanagra).
An unusual species mix
New Zealand’s land bird fauna is unusual and restricted. This is in part because of where they came from, and how long ago they or their ancestors arrived. Another factor is that certain other animal groups that are common elsewhere did not reach New Zealand.
Origins of the land birds
Most of New Zealand’s land birds’ ancestors can be traced back to two sources:
- those that were ‘on board’ New Zealand when it broke away from the supercontinent of Gondwana 85 million years and began its long drift to its present location
- those that reached New Zealand across the ocean, mostly from Australia.
Oldest resident species
The first group includes the most unusual bird groups – the wren and maybe the wattlebird families, and the endemic parrot family Strigopidae, which includes kākāpō, kākā and kea.
These birds evolved in ancient forests at the time of the dinosaurs. While mammals were evolving elsewhere, New Zealand bird species remained isolated. With no land mammals apart from bats, and no predatory snakes, the birds could evolve in unique ways. In particular, they had less need to fly as an escape strategy, and could safely feed on the ground.
Migrants from Australia
The ancestors of the second group were apparently blown across the Tasman Sea from Australia. Some came via New Caledonia. They include:
- the tūī and the bellbird (korimako, Anthornis melanura)
- weka (Gallirallus australis)
- fantail (pīwakawaka, Rhipidura fuliginosa).
All of these except the fantail have been in New Zealand long enough to evolve quite differently from their Australian ancestors – the weka and takahē becoming flightless.
Over the millennia, land bird species arrived from Australia from time to time, carried by strong westerly winds. But relatively few became established. This might be because they were ill-adapted to their new habitat. But as humans have cleared large areas of land, more self-introduced Australian species have become well established. This includes the silvereye (whose Māori name, tauhou, means stranger) and the welcome swallow (Hirundo neoxena).
A few species came from other places, and the origins of others remain unclear. There has even been debate over the origin of the kiwi. Some scientists maintained its ancestors were on New Zealand when it split from Gondwana, and others suggested it was an early arrival from Australia. In 2015 DNA research showed that the kiwi's closest relative was the extinct giant elephant bird, Mullerornis agilis, from Madagascar.
New Zealand’s recently extinct Haast’s eagle was the world’s largest eagle. With claws like a tiger’s, it attacked and killed large birds including the giant moa. Weighing 12 kilograms, it had a 3-metre wing span. Its closest relatives include Australia’s little eagle Aquila morphnoides), which weighs just 1 kilogram. They all shared a common Australian ancestor about a million years ago, showing how quickly a new environment can shape the evolution of a species.
Eighty-five of New Zealand’s 91 species of native land birds are endemic (they occur nowhere else). In comparison, the British Isles have just one endemic species. Only remote oceanic islands such as Hawaii have a similarly high proportion of endemic land birds.
Endemic families and orders
More importantly, some of those endemic species belong to entire families or orders that are endemic to New Zealand. This means that even their nearest relatives in other countries are only very distantly related. Few countries have such a high number of endemic families or orders.