Biology and conservation of the endangered Hawaiian Dark-rumped Petrel (Pterodroma phaeopygia sandwichensis)
Simons, Theodore Raymond
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The Hawaiian Dark-rumped Petrel or 'Ua'u is an endangered gadfly petrel that nests in the Hawaiian Islands and ranges throughout the central Pacific. The species was once common in Hawaii, with large colonies located on all the main islands, but its numbers have recently been reduced to several small relictual populations. Over 85% of the breeding birds known today nest in and around Haleakala National Park on the island of Maui, the site of a three-year study begun in 1979. The study employed a multidisciplinary approach in an attempt to understand the breeding biology, behavior, and conservation needs of this poorly known species. The attendance patterns and behavior of breeding birds were monitored using specially designed event recorders and a closed circuit television system employing a night vision scope. Over 280 hr of direct observations at one nest were recorded. A conventional breeding biology study documented the bird's breeding chronology and variations in reproductive success that occurred naturally, and as a result of varying levels of predation by introduced mammals. These findings were used to develop a computer simulation population model that examined the impact of changing levels of predation and reproductive success on the rate of growth or decline of the Haleakala population. A study of the physiological ecology of breeding birds was undertaken to examine the adaptations of the Dark-rumped Petrel's eggs, and those of adult birds and nestlings, to the factors that constrain their breeding cycle. These factors include an apparently unpredictable and widely dispersed food supply, and a nesting colony located at an elevation of 3000 m, one of the highest in the world. This involved an analysis of the water-vapor conductance and shell structure of the egg, and the development of a reproductive energy budget. The energy budget incorporated measurements of the metabolic rates of adults and developing nestlings, the feeding frequencies and growth patterns of chicks, and the energetic content of nestling food. The study has improved our understanding of breeding ecology of the Procellariiformes, and identified the primary conservation needs of the endangered Dark-rumped Petrel.
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