The Tahiti monarch used to be common throughout the island, but during the last century populations underwent a dramatic decrease, and now number less than 50, restricted to a few valleys. These perilous declines have largely been the result of the accidental introduction of the black rat (Rattus rattus) to the island, which prey on the eggs and chicks. However, two introduced birds, the Indian mynah and red-vented bulbul, also pose a significant threat to the monarch’s survival. It is thought that the Indian mynah, which was introduced to control wasps, preys on eggs and chicks, whereas the red-vented bulbul competes with the monarch for nest sites and territories (5).
Introduced plants, as well as animals, are also having a negative impact on the Tahiti monarch in some areas. A dense, invasive shrub, Miconia calvescens, was introduced in 1937, and is changing the composition of the forests (2), and presumably altering the areas where the Tahiti monarch likes to nest and feed, such as in Mont Marau, where a population was found in 1980 and is now extinct (6). Four other Pomarea flycatcher species have already become extinct, which highlights the susceptibility of monarch birds to such threats (1). Additionally, as this species is restricted to a very small area, it is very vulnerable to any chance events, such as hurricanes, which could rapidly affect all the individuals in a population.