Nicole Bilodeau: "The effects of nutrition on disease prevalence and lamb survival in two populations of bighorn sheep in Idaho."
Student Spotlight: Nicole Bilodeau
Major Advisor: Ryan Long
Idaho Department of Fish and Game (IDFG) has been studying bighorn sheep populations for decades, and has learned a lot in the process. For example, we now know that disease, and pneumonia in particular, is the cause of depressed bighorn sheep populations in some parts of Idaho. However, we also know that poor nutrition can predispose wildlife to increased mortality from disease, making it critical to understand relationships between nutrition and disease dynamics in bighorn sheep. Over the next few years we will be studying the effects of nutrition on disease prevalence and lamb survival in two populations of bighorn sheep in Idaho. This research was initially developed and funded by IDFG as an extension of an ongoing management project.
The project is currently comprised of 49 ewes collared with GPS transmitters in two study sites: the Owyhee River (OR) and the East Fork of the Salmon River (EFSR). Both sites have unique habitats and bighorn sheep populations: the OR is characterized by Great Basin type habitats and California bighorn sheep, whereas the EFSR is characterized by diverse high-elevation habitats and Rocky Mountain bighorn sheep. At both sites we conducted aerial surveys during spring 2017 to count the number of newborn lambs associated with collared ewes and then we monitored lambs from the ground throughout the summer and early fall. We will use these observations to help us estimate lamb survival rates. In addition to lamb surveys, we set up habitat phenology plots at each site, which we revisited on a monthly basis throughout the summer to track stages of plant growth (i.e., new growth, flowering, fruiting, mature, cured) and forage availability. We also collected fecal pellets from adult sheep to determine their forage selection and diet composition. Essentially, we want to determine what the sheep are selecting to eat vs. what plants are available for them to eat during the summer and then evaluate the abundance and nutritional quality of those plants. Lastly, to assess disease prevalence we are collecting blood, mucus, and tissue samples from sheep when they are collared and from any fresh carcasses.
When field work begins again in spring 2018 we will be adding two additional surveys that will help us to evaluate the nutritional quality of the landscape at each site. First, we will conduct habitat composition surveys, which will allow us to assess plant species composition and availability of key species during the peak of the growing season. Secondly, we will be estimating forage biomass and collecting plant samples to determine how much forage is available to sheep and the nutritional content of each plant species. These surveys will help us to compare the nutritional quality of the landscape between our two study sites.
Lambs are the next generation of our bighorn sheep populations, which is why it is important to understand the complex factors that influence their survival. This research will benefit wildlife managers to make critical decisions about harvest, habitat restoration and use, and maps for domestic contact that will impact bighorn sheep. This past summer was the first of three field seasons, so we still have a lot of work ahead of us.