New Zealand may have been home to as many as 2.5 million moas, new research has revealed.
The study, published in the academic journal Ecography, gathered the body mass and population densities for living flightless birds then controlled for their habitat and the effects of predators and humans.
They then applied this approach for each of the nine extinct species of moa which lived in New Zealand about 1000 years ago - before human arrival.
The research revealed the mean national density of moa ranged between two and ten birds per square km - or between 0.5 and 2.5 million moas at the same time.
"In general, the heavier an animal species is, the lower its population density (the numbers of a species that can be supported in an area of land)" says Manaaki Whenua - Landcare Research scientist Dave Latham.
"This is because larger animals need more energy resources (food/water) to survive. This relationship is strong for living species of flightless birds and therefore it can be used to estimate densities of extinct species of flightless birds".
Although the research gives similar current population densities for large herbivorous wild mammals introduced to New Zealand - like deer - the authors point out this doesn't mean they have the same impact "as many other factors affect the way large herbivores affect their environments".
It's hoped the scientific modelling could improve population estimates for other large prehistoric flightless birds around the world.
"Population sizes and densities are important aspects of the ecology of extinct species, but are often overlooked because they are difficult to estimate," Latham says.
"But such data are key, not only for understanding the roles these species once played within their ecosystems, but also in understanding the processes that ultimately led to their extinction."
