Disease and ectoparasite management improve nestling golden eagle health and survival: An effective mitigation strategy

Abstract

Changes in the distribution and behavior of pathogens and parasites associated with climate change are creating emerging threats for wildlife. These threats have created an urgent need for conservation strategies to manage wildlife. Conservation strategies could provide reliable and cost-effective compensatory mitigation options for protected species affected by renewable energy production, such as golden eagles (Aquila chrysaetos). We used nest camera data to assess survival and cause of death for golden eagle nestlings in southern Idaho, USA. Together, poultry bugs (Haematosiphon inodorus), a blood-sucking ectoparasite that lives in golden eagle nests, and trichomonosis, a fatal disease that is transmitted through the consumption of rock pigeons (Columba livia) caused [~] 27% of nestlings to die per year. From 2022--2023, we treated trichomonosis-infected nestlings with an anti-protozoan drug and developed a protocol for reducing poultry bug densities in eagle nests, then we projected the effects of disease and parasite treatments on population growth using simulation models. We collected pre-treatment information on nestling health and survival, and then, after young fledged, we applied 1 of 3 experimental parasite treatments to eagle nests: permethrin and diatomaceous earth, diatomaceous earth only, or water - a control, and measured effects on eagle health and survival the following year. Ten eagle nestlings with trichomonosis, that otherwise would have died, were successfully treated and lived to fledge from the nest. The permethrin and diatomaceous earth treatment significantly reduced poultry bug densities in eagle nests in the subsequent breeding season and created measurable improvements to nestling health and survival. Nestlings had significantly higher hematocrit, female nestlings had higher mass, and, on average, more nestlings (0.70) successfully survived to fledge compared with control- and diatomaceous earth-treated nests. Further, treatment of disease and parasites was projected to increase population growth rates by 4% and 8%, respectively. In total, we estimate saving 17.5 nestlings, which equates to 10.2 adult eagles, through disease and parasite treatments in two years. In areas with dense concentrations of poultry bugs or where eagles consume rock pigeons, disease and parasite treatments could be an effective compensatory mitigation option or management tool with population-level impacts on eagle populations.