The Hawaiian Islands host three non-native species of rats. Polynesian rats (Rattus exulans) arrived with Hawaiians about 1600 years ago and since then both black rats (Rattus rattus) and Norway rats (Rattus norvegicus) have arrived with Europeans. Besides being a pest around human habitation and a threat to human health, these species have a large impact on the native ecosystem as both predators and competitors. Rats are agile tree climbers and at least one of the three species is found in all native habitats. Introduced rats are known to prey on eggs, nestlings, and adults of Hawaii's native forest birds. Additionally, they compete with forest birds for food items such as native snails, insects, fruits, and seeds. As a result, rats are regarded as a major factor in the decline of Hawaii's endemic forest birds and as a barrier to the recovery of endangered forest birds. They also prevent the re-growth of many native plants by eating fuits and seeds.
Effective predator control of these animals helps to alleviate their impact on forest bird populations.