I’ve often thought about what it would be like if the moa and Haast’s eagle had not gone extinct. Would Haast’s eagle prey on us? Would common news items feature unsuspecting people getting trampled by moa?

With a wingspan of 2.6-3.0m and a weight of around 10-15kgs Haast’s eagle preyed on moa, so preying on humans would have been easy enough for them. The largest of the moa reached a height of 3.6m and weighed around 230kgs.

But why did the moa and Haast’s eagle evolve on New Zealand to become so big? There is a phenomenon called island gigantism. When an island is void of large mammalian carnivores the reptiles and birds present evolve into the niches otherwise occupied by the mammals. This can have the effect of causing the reptiles and birds to evolve larger than they normally would have. One of the reasons why is that with predators these herbaceous creatures remain small, which makes it easier for them to hide. However without predators there isn’t this pressure, allowing for them to grow bigger in size with no disadvantage for doing so.

Moa still existed in New Zealand at the time of the arrival of the Maori. While there are no accounts of the moa trampling people, the Maori hunted the moa for food, and within 100 years they became extinct. This in effect had a massive impact on the Haast’s eagle in consequence of the disappearance of their primary food source. Their population could not be sustained and they followed the moa to extinction soon after, in 1400. This is but one example of how interrelated the ecosystem is and that just the changing of one thing can have massive effects on other parts of the ecosystem.

Even though Haast’s eagle could have potentially been a predator to us, I still think it would be awesome to behold one out in the bush, or have a gigantic moa suddenly step out onto the path in front of me. It would have added another giant level of spectacular beauty to New Zealand’s unique ecosystem.