Date of Award:
Master of Science (MS)
Arnaud Van Wettere
Ferruginous Hawks are a bird of prey species that nest in sagebrush steppe and grassland habitat. These birds are threatened by habitat loss and fragmentation from urbanization, rural development, oil and natural gas extraction, habitat treatment projects, and wildfires, and experiencing widespread population declines across their breeding range. Because of this, Ferruginous Hawks (FEHAs) have been deemed a Species of Greatest Conservation Need by state management agencies in Utah, Idaho, Wyoming and Nevada. The health and survival of Ferruginous Hawk (FEHA) nestlings is crucial to long-term population viability. Understanding the threats these birds are facing as nestlings can provide valuable insights into what challenges their populations are facing, but factors that can affect FEHA nestlings’ survival are largely understudied. Developing a better understanding of this topic this will provide valuable insights into population dynamics and will inform management strategies. We looked at two different factors that may affect nestling health and survivorship: 1) how reuse of nests from one year to another affected parasite loads of nestlings, nest reuse affected parasite loads of nestlings, and 2) how a nests’ proximity to recreational shooting affected blood lead levels in nestlings. Artificial nesting platforms have been put up in areas where FEHAs nest. FEHA nesting territories usually are made up of nests built on trees or rocky substrate. It is thought that numbers of platforms available within FEHA nesting territories are more limited than in areas with natural nesting substrate. Nest structures can serve as a mini habitat for insects, including avian ectoparasites, so nest reuse may contribute to higher parasite loads in areas with fewer alternate nest options. We collected ectoparasites and blood samples from FEHA nestlings across Utah, Idaho, Wyoming and Nevada during the 2020 and 2021 breeding season to quantify the parasites living on and within the nestlings, also known as parasite loads. We did not detect hemoparasitic DNA in blood samples, and found that ectoparasite loads were low, and did not vary significantly on nests with differing amounts of reuse. This study demonstrates that nest reuse does not affect parasite loads for nestlings in our study areas. Lead toxicity threatens birds of prey globally, and birds exposed as nestlings can face long term negative effects. Nest sites surveyed during both years in Idaho were located on the Morley Nelson Snake River Birds of Prey National Conservation Area, which is a key habitat for breeding birds of prey. This area also has well documented high recreational shooting activity. For the second component of this study, we compared blood lead levels from nestlings in Idaho, Wyoming and Utah during the 2020 and 2021 breeding seasons. We found nestlings from Idaho sites had detectable levels of lead in their blood, while nestlings from Utah and Wyoming did not. These findings indicate that proximity to recreational shooting is exposing nestlings in Idaho to lead ammunition. To alleviate this, it could be useful to consider changing shooting allowances or ammunition restrictions. By looking at nestlings’ parasite loads and blood lead levels, this study establishes an important of some threats nestlings’ face.
Juhlin, Ellis A., "Bugs, Bullets and Birds: Factors Affecting the Health and Survival of Ferruginous Hawk Nestlings in the Intermountain West" (2022). All Graduate Theses and Dissertations. 8627.
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