Foraging Ecology & Conservation Physiology of the Mottled Petrel, Pterodroma inexpectata, with Applications for Maximising the Success of Petrel Conservation
Globally, we face a biodiversity crisis driven by anthropogenic impacts on environmental and ecological integrity. To maximise our conservation efforts, we must understand how populations respond to environmental change and the mechanisms that enable their response. Critically, we need to be cautious of the additive threats of research and conservation action on already stressed populations. Procellariiform seabirds are one of the most threatened avian orders in the world. The conservation management of many species within this group is hampered by a lack of basic species knowledge, including reproductive biology, physiology and spatial extent. Efforts to obtain information to aid the research and conservation of seabirds often requires manipulation, including handling of both adults and chicks. Repeated exposure to stressors, including environmental fluctuations and handling, can induce chronic stress in vertebrates and our understanding of stress reactivity in procellariiform chicks is contradictory at best. In this thesis, I investigated key ecological and physiological factors that will contribute to the successful recovery of mottled petrels (Pterodroma inexpectata), which has implications for other petrel species. This study consisted of two major components. Firstly, I conducted the only study to date of mottled petrel breeding biology and foraging ecology during the chick-rearing period across multiple seasons to determine the parameters that provide insight into inter-seasonal variation in breeding success. Mottled petrels exploit a previously undescribed foraging niche in polar waters during chick-rearing, confirming that small gadfly petrels are capable of long-distance foraging trips during breeding. Mottled petrels are flexible foragers and appear to cope with prey limitations better than other sympatrically breeding procellariform species by adapting their foraging range and diet to maximise breeding success. Mottled petrel chick growth did not alter between years even when faced with nutritional restrictions, though in these years, chicks fledged earlier and in poorer condition. This lack of developmental plasticity is intriguing in a group where phenotypic adjustments mediated by stress hormones are thought to support the survival of individuals that are faced with unpredictable environments. Secondly, I provide the first measures of stress reactivity in mottled petrel chicks throughout development. This allows us to answer whether research- and conservation management-relevant levels and intensities of handling induced chronic stress in chicks. Semi-precocial, mottled petrel chicks were capable of mounting an adult-level stress response from hatching, a trait previously linked to fully precocial species. Regular handling and translocation activities did not appear to induce chronic stress in mottled petrel chicks. Chicks that were exposed to high levels of handling appeared to habituate to this stressor and their development and condition were not affected. Chicks that were exposed to moderate levels of handling, or high levels of handling over a short period, continued to mount a stress response though regular exposure to corticosterone induced by handling did not alter chick growth and development. These findings show that mottled petrels have a limited capacity to alter their growth in response to high levels of corticosterone. It is possible that corticosterone may play a role in energetic regulation in this species, which are fed less frequently relative to their body size than other species within the procellariiform group. To confirm this, wider testing of stress responses in procellariiform species is needed. The resilience of mottled petrels to fluctuations in prey quality and location during breeding, as well as to stress induced by common management practices, bodes well for continued conservation efforts around New Zealand, and potentially more widely for petrels. This thesis confirms that the integration of ecological and physiological studies facilitate sound conservation management of vulnerable populations, especially in this unprecedented time of change.
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