Moa were present in New Zealand on the mainland and the major nearshore islands of Great Barrier, D’Urville, and Stewart Island. These were connected to the mainland during the ice ages, when the sea level was low.
It was once thought that moa were exclusively grass-eating and lived only on grassy plains. It is now accepted that the coastal plains were originally forested, and that these vegetarian birds browsed trees, shrubs and herbs as well as grasses.
Usually, three or four moa species lived together in a habitat that had particular vegetation types:
- The coastal dunelands of the North Island, with their mosaic of grassland, shrubland and forest, harboured the Euryapteryx assemblage, particularly the stout-legged moa and Mantell’s moa.
- In the low rainfall zones of the eastern South Island, although the vegetation was slightly different, the Euryapteryx curtus or stout-legged moa was dominant. There were also heavy-footed moa.
- Where there were swamp forests (none now survive), the eastern moa was most common.
- Closed canopy forests were occupied by the little bush moa, with a few Mantell’s moa.
- Mountainous and subalpine zones up to 2,000 metres in the South Island were the stronghold of the upland moa, along with the crested moa.
Giant moa of the Dinornis genus were present in all habitats, from sea level to the subalpine zone, but generally were less common than smaller moa.
There has been much debate as to whether the moa’s browsing gave rise to the small-leaved, highly branched form of many New Zealand plants. Some believe that shrubs evolved spiky twigs to deter moa. Others suggest that the tangled form is an adaptation to the climate, especially strong winds.
Analysis of fossilised excrement and crop and gizzard contents preserved in swamps suggests that moa ate a variety of shrubs and trees. However, moa foraging at heights up to 1,800 metres on a site such as Mt Owen (in north-west Nelson) must have eaten grasses and herbs, since no shrubs or trees existed there above 1,200 metres. Heavy-footed moa are known to have lived in areas rich in loess (fine, wind-blown sediment) and with little vegetation. Each of the six genera of moa had different shaped beaks and gizzard structures, indicating they were adapted to different plants.