Population Ecology of the Mariana Swiftlet (Aerodramus bartschi) on O'ahu, Hawaiian Islands Public Deposited



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  • The Mariana Swiftlet (Aerodramus bartschi) (Aves: Apodidae) is endemic to the Mariana Islands, where it currently occurs on Saipan, Aguiguan, and Guam. An introduced population of Mariana Swiftlets is also present on O'ahu in the Hawaiian Islands. Sparing interference with the endangered population in the Marianas, the introduced, surrogate population on O'ahu was studied in and around a human-made tunnel used for roosting and nesting from July to September 2005, and December 2005 to January 2011. In order to implement effective conservation efforts, it is critical to understand species life history activities throughout multiple phases of the annual cycle. Information on Mariana Swiftlet life history is scarce. Therefore, this study was initiated to obtain critical data to provide the U.S. Fish and Wildlife Service, Commonwealth of the Northern Mariana Islands Division of Fish and Wildlife, and Guam Division of Aquatic and Wildlife Resources with the relevant information for addressing recovery criteria, as well as designing and implementing the proposed reintroductions of swiftlets from Saipan and southern Guam to their former ranges of Rota and northern Guam, respectively. Mariana Swiftlets are open-air foragers that may be susceptible to the impacts of wind turbines if wind energy facilities become widespread in the Mariana Islands. Implementing effective survey methods is critical to determine a reliable baseline of Mariana Swiftlet population size, particularly if wind turbines are situated or proposed to be placed in the feeding ranges of these insectivores. I summarized the current and historic distribution and abundance, as well as described the survey methods used to evaluate the status of the Mariana Swiftlet. Using existing literature, correspondence from relevant biologists, and population surveys on O'ahu, the present range-wide population of Mariana Swiftlets is estimated to be 6,532 individuals occurring in 17 caves on Saipan, Aguiguan, and Guam; and 142 individuals occupying one tunnel on O'ahu. Based on a literature review, I confirmed that swiftlets have been extirpated from Rota and Tinian, and have declined on Aguiguan supporting their listing as an endangered species. Swiftlets have remained relatively stable on Guam and Saipan in recent years. An assessment of survey methods used for Mariana Swiftlets suggests changes are needed to more accurately reflect their distribution and abundance. The behavioral ecology and reproductive biology of the Mariana Swiftlet on O'ahu were examined at multiple temporal scales over five annual cycles. Tunnel emergence and arrival surveys indicated that peak entering and exiting activity occurred during crepuscular hours. Overnight surveys documented entering and exiting swiftlets at all hours of the night, with the latest arrival at 0402 hours. Active nests were observed in every month of the year. Peak nesting activity occurred between about May and September, and decreased from October to April. A clutch of one white egg (n = 478) was laid in a nest that was secured to a ledge or tunnel wall with copious amounts of mucus-like salivary cement. Mean incubation and nestling periods were 23.91 ± 3.30 days (range = 18-30, n = 233) and 55.04 ± 6.61 days (range = 41-84, n = 228), respectively. Estimated nest success was 63%. Eggs found in the water or mud, or on the tunnel floor accounted for 52% of nest failures. Rat depredation was an important cause of nest failure and often resulted in simultaneous loss of most nests. Mariana Swiftlets completely recycled breeding activities following rat depredation events. The daily survival rate of nests was influenced by a quadratic effect of nest age and year. Having a surrogate population on O'ahu to learn more about natural history, test reintroduction techniques, and provide individuals for population enhancement in the Marianas is an important advantage for Mariana Swiftlet conservation efforts.
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