Date of Final Oral Examination (Defense)
Type of Culminating Activity
Master of Science in Raptor Biology
Julie Heath, Ph.D.
Ian C. Robertson, Ph.D.
Michael N. Kochert, M.S.
Climate and anthropogenic land use changes can alter biological communities and affect disease infection rates and parasite species distribution and abundance. Management to mitigate the threats of emerging infectious diseases and parasite species requires identifying and understanding factors that influence individual susceptibility within populations. Golden eagles (Aquila chrysaetos) in southwestern Idaho face several current and emerging threats, including a landscape-mediated diet shift that has increased the potential for disease infection, and warming temperatures that may increase the distribution and abundance of hematophagous ectoparasites. We examined prevalence of Trichomonas gallinae infection in golden eagle nestlings across western North America in 2015 and conducted a detailed study of the risk factors associated with T. gallinae infection in southwestern Idaho. We also quantified the abundance of Mexican chicken bug (Haematosiphon inodorus; Hemiptera: Cimicidae) in golden eagle nests in southwestern Idaho in 2015 and 2016. We developed a pit fall trap method to measure H. inodorus abundance, investigated factors that might affect abundance in nests, tested the ‘nest protection’ hypothesis that eagles modify nest sites to reduce the effects of ectoparasitism, and measured the physiological effects of ectoparasitism on nestlings.
In our study of T. gallinae, we found a 6% infection rate distributed broadly across our western North America study area, with a relatively high T. gallinae infection rate, 41%, in Idaho. The probability of T. gallinae infection increased as the proportion of rock pigeons in nestling diet increased. Landscape-level change in southwestern Idaho is related to an increase in eagle diet diversity, and an increase in rock pigeons in nestling diet increased the probability of T. gallinae infection.
In our study of H. inodorus, we found that eagles reuse less parasitized nests in successive years, and that south-facing nests and nests with later phenology had higher H. inodorus abundance. We found support for the ‘nest protection’ hypothesis. Golden eagles selected gray rabbitbrush as nest material, a plant that has high phenolic concentrations relative to others available on the landscape, and aromatic nest material had a positive effect on nestling hematocrit, suggesting these nest additions reduced the effects of ectoparasitism on nestlings. We found that increased ectoparasitism reduced nestling mass and hematocrit, and increased the probability that nestlings either fledged early or died in the nest. Nestling circulating corticosterone, which may act as a mechanism in the timing of fledging behavior, increased relative to ectoparasite infestation levels.
Our results suggest that the current and emerging threats of disease and ectoparasites have the potential to negatively affect golden eagle productivity in southwestern Idaho. Although our data suggest there is a low incidence of T. gallinae infection in golden eagle populations across western North America, shifts in eagle diet, that result from habitat degradation and loss of historical prey resources, have the potential to affect golden eagle nestling survival. In addition, the presence and intensity of ectoparasitism affects the physiological condition of young eagles, and changes to the landscape in southwestern Idaho may reduce the ability of eagles to ‘defend’ their nests from the effects of ectoparasitism with aromatic plants. Given the projections of current climate trends, continued monitoring of the effects of disease and ectoparasites on golden eagle populations will be important for future conservation.
Dudek, Benjamin Michael, "The Role of Disease and Ectoparasites in the Ecology of Nestling Golden Eagles" (2017). Boise State University Theses and Dissertations. 1289.