The European discoverers found New Zealand clothed in extensive areas of forest, and among the forest birds were included some of the most remarkable species in the fauna. Forest-inhabiting birds were affected by widespread changes within a short period after European settlement. Habitat was rapidly reduced as forest was transformed to farm land, and the birds, vulnerable through long isolation, were subjected to the rats, mustelids, and other mammals introduced by man. A few accounts left by early naturalists enable some impression to be formed of the original bird life, but the opportunity to understand fully the relationships of the native birds in the economy of the forest has been lost.
Prominent in the primitive forests were the birds of a remarkable endemic family, the “wattle birds” (from their conspicuous chin wattles), but this family unfortunately proved almost incapable of surviving changed conditions. Originally the most widely distributed species, the black-and-brown saddleback (Philesturnus) probably exists now only on a few off-shore islands; in the forest it fed both on fruit and on insects, observations on recent visits to the islands suggest that it foraged among litter on the forest floor. The kokako (or “native crow”) (Callaeas), mainly a leaf and fruit eater, lived more exclusively at higher levels in the trees: there are still extensive forest areas in the North Island (and possibly a few localities in the South Island and Stewart Island) which contain remnants of this large, handsome, blue-grey species The saddleback and kokako are represented by separate subspecies in North and South Islands; in the kokako this difference is a striking one, the wattles in the North Island subspecies being bright blue, and in the South Island subspecies, orange. The third member of the family, the huia (Heteralocha), had a remarkably limited distribution, inhabiting only the mountain and lowland forests of the south-eastern portion of the North Island. This, perhaps the most distinctive member of the bird fauna characterised by the marked difference between the bills of male and female, is the only forest bird which became extinct as the result of the European settlement of New Zealand. The huia had a clearly defined role in the primitive forest, as it fed largely upon the insect larvae in rotting and fallen limbs and trunks; the stout bill of the male would be employed to break open the decaying material, while the female used her long, curved bill to probe into crevices. The saddleback, which moves in family parties or small flocks, constantly gives a penetrating, chattering call. It also has a soft, flutelike song, and soft musical notes were sometimes delivered by the huia; the kokako is noted for its powerful, flutelike song.
While there is fortunately not a long list of native forest birds that, like the wattle birds, were brought low by the coming of European man, a number of species have survived only in the larger tracts of forest. The native thrush (Turnagra), a handsome forest species of warm brown and reddish plumage, was well known as a tame and confiding visitor to the camps of explorers and bushmen, but it declined suddenly after settlement began, and is now extremely rare; there are separate subspecies in both main islands. The bush wren (Xenicus longipes), now local and rare, was originally of wide distribution in the mountain districts of the South Island and the central and southern North Island. Still widely distributed in the deeper forests are the following: kaka (Nestor meridionalis), the parrakeets (Cyanoramphus), robin (Miro australis), whitehead (North Island only) (Mohoua albicilla), and yellowhead (South Island only) (Mohoua ochrocephala). Finally, the stitchbird (Notiomystis), a colourful honeyeater found originally in North Island forests and apparently common over much of the island, proved to be extremely susceptible to change. This species disappeared completely on the mainland, but Little Barrier Island bird sanctuary still has a thriving population.
Another group comprises the portion of the original forest bird fauna evidently less sensitive to, or capable of gaining some advantage from, the changes brought about by settlement. These species still have a wide area of distribution both in the more extensive native forests and in smaller remnants. They have also to a varying degree colonised the exotic tree plantings established in the early days of settlement, while some are becoming strongly entrenched in afforestation tracts. The following may be placed in this category: kiwis (Apteryx), weka (Gallirallus), New Zealand pigeon (Hemiphaga novaeseelandiae), shining cuckoo (Chalcites lucidus), long-tailed cuckoo (Eudynamis taitensis), morepork (Ninox novaeseelandiae), rifleman (Acanthisitta chloris), fantail (Rhipidura fuliginosa), tomtit (Petroica macrocephala), brown creeper (South Island only) (Finschia novaeseelandiae), grey warbler (Gerygone igata), bellbird (Anthornis melanura), tui (Prosthemadera novaeseelandiae), and silvereye (Zosterops lateralis). Several species are familiar in garden or park, especially the grey warbler, fantail, and silvereye, as well as the two honeyeaters, the bellbird and tui. The latter are readily attracted into densely settled districts to nectar-bearing trees or shrubs. The two cuckoos are summer visitors which breed in New Zealand and leave in autumn for their winter quarters in the tropical Pacific; the cuckoos are New Zealand's only land-bird migrants. The shining cuckoo, common in settled districts, has the parasitic breeding habits characteristic of the family and places its egg in the nest of the grey warbler.
The kiwis and weka – flightless birds – were a notable feature on the forest floor in the original forests. Although ground living, these birds suffered less than would be expected from the presence of predatory mammals, and the three species of kiwi especially are still well established. The kiwis occur mainly near the larger forest areas but they also feed and nest in adjacent scrub land or rough farm land. A severe decrease was suffered by the weka in most areas, but it is recovering strongly and may again become widespread.