These two species of rats were introduced to New Zealand by the first Polynesian settlers around 1,000 years ago. They quickly became established and spread throughout the country, preying on native birds, their eggs and chicks. The giant eagle (Hieraaetus moorei) was one of the largest and most powerful birds of prey in New Zealand and had no natural predators. However, it was unable to defend itself against the rats and was driven to extinction within a few hundred years of their arrival.
The introduction of rats to New Zealand had a devastating impact on the native bird population. Many species were driven to extinction, and those that survived were often reduced to a fraction of their former numbers. The loss of these birds had a profound effect on the New Zealand ecosystem, and it is still felt today.