Avian diseases, especially avian malaria and avian pox, are one of the greatest factors leading to the decline of native Hawaiian birds (van Riper and van Riper 1986, Banko et al. 2001, van Riper and Scott 2001). According to Jacobi and Atkinson (1995), a major avian malaria and avian pox epidemic in midelevation forest birds was documented during a National Biological Service study in 1992. Avian malaria is probably the most important factor preventing endemic bird populations from recovering in low elevations (Jarvi et al. 2001). Many introduced birds develop nonfatal infections that can be transmitted to other birds by introduced mosquitoes.

Mosquito-borne diseases are a relatively new problem for Hawaiian birds. Culex quinquefasciatus, the mosquito that serves as a vector of avian malaria and avian pox, was not present in Hawaii until it was unwittingly introduced into Maui in 1826 when sailors dumped water containing larvae from Mexico into a stream while refilling their water dregs (Warner 1968). Before this event, mosquito transmitted diseases were not a threat to the Hawaiian avifauna even though migrating birds may have harbored malaria infections. The Culex mosquito has spread to all of the islands, but it is mainly in low to midelevation areas because this subspecies is typically found below around 600 m above sea level (Warner 1968). Mosquitoes can inhabit areas as high as 1800 m above sea level in some years when conditions are favorable (VanderWerf 2001). More...