The Mariana swiftlet is endemic to the Northern Mariana Islands of Guam, Rota, Aguiguan, Tinian, and Saipan, but are currently found only on Guam, Aguiguan, and Saipan. Population declines and their limited distribution prompted the United States Fish and Wildlife Service to list this species as endangered in 1984. Swiftlets were once common on the island of Rota but were extirpated after 1976. Aerial application of pesticides in the 1960s and 1970s on Rota may have reduced prey resources resulting in their extirpation.
A primary objective of the 1992 species recovery plan was reintroduction of swiftlets from the island of Saipan, where the species occurs in reasonable numbers, to Rota. Before translocation we had to describe and quantify swiftlet diets on Saipan and compare the relative prey abundance of insect communities on Rota and Saipan. We sampled aerial insects on both islands during the wet and dry seasons using aerial malaise traps and sticky traps suspended above the tree canopy and low sweep nets to quantify prey abundance. During aerial survey periods on Saipan, we collected fresh guano samples in pans placed below nest and roost sites in caves to describe swiftlet diets. We compared our insect samples to reference samples prepared from the aerial collection. Preliminary comparisons of insect communities between Rota and Saipan indicate the prey in swiftlet diet on Saipan is available as a food resource on Rota. Thus, translocation of swiftlets from Saipan to Rota remains a viable option for the recovery of this species.