Post-Breeding Distribution of Wedge-Tailed Shearwaters (Ardenna Pacifica) Nesting on Oahu, Hawaii and Associated Geolocator Device Effects
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Authors
Piauwasdy , Alyssa Bernadine
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Marine Science
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Abstract
The use of animal-borne sensors, or biologging, has greatly enhanced our understanding of the at-sea ecology of seabirds, improving conservation efforts. In this thesis, I present a literature review on the application of light-level geolocators in shearwater and petrel migration studies and investigate the post-breeding distribution and effects of geolocator deployment on Wedge-tailed Shearwaters (Ardenna pacifica) from the Freeman Seabird Preserve in Oahu. By deploying geolocators on adult shearwaters across two contrasting El Niño Southern Oscillation (ENSO) phases, La Niña (2022-23) and El Niño (2023-24), my goal was to advance understanding of tropical seabird migration and assess the effects of geolocator attachment under varying oceanographic conditions. Potential device effects were tested by comparing the growth of chicks between tagged and non-tagged parents and the adults' rate of return to the colony across two breeding seasons. Although there were no significant negative effects of geolocators (< 1% body mass) on chick growth or adult return rates, there were lower peak body masses and slower wing chord growth in chicks overall in the El Niño year. While geolocators did not impact adult survival or breeding performance, subtle interactions among device deployment, sex-specific traits, and environmental variability may emerge during periods with more challenging conditions. Following breeding, shearwaters consistently migrated to coastal and pelagic waters off Central America in the eastern tropical Pacific (ETP), irrespective of ENSO phase. However, during the El Niño year, the timing of departure from the breeding colony and arrival to the ETP were delayed. In non-breeding areas, shearwaters shifted to more diurnal foraging and expanded their foraging range during El Niño. Because most of their time was spent within international Exclusive Economic Zone waters, findings highlight the importance of collaborative, multinational conservation efforts.
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Hawaii Pacific University