Survival and movement of mule deer and white-tailed deer in Nebraska with implications for the spread of chronic wasting disease and hemorrhagic disease

Management of mule deer (Odocoileus hemionus) and white-tailed deer (Odocoileus virginianus) in Nebraska was complicated by the emergence of chronic wasting disease (CWD) in western Nebraska in 1997. The disease is fatal and contagious, but transmission dynamics are largely unknown. Outbreaks of hemorrhagic disease (HD) due to infection by epizootic hemorrhagic disease and bluetongue viruses can provide a significant source of mortality in populations of deer in Nebraska. Domestic cattle are also susceptible to HD, which is spread by midges of the genus Culicoides. We used radio telemetry to determine survival and fecundity rates of the low-density (0.5-1.5 deer/km2) population of sympatric mule deer and white-tailed deer in Morrill County, Nebraska and the high-density (20-30 deer/km2) population of white-tailed deer in DeSoto National Wildlife Refuge. We generated daily survival rates by sex, location, and month of the year using Bayesian hierarchical regression models. We estimated annual survival of 68% and 38% for female and male deer, respectively, in western Nebraska, and 74% and 47% for female and male deer, respectively, in eastern Nebraska. We simulated movement of deer in eastern and western Nebraska using an individual-based model. We used the estimates of survival and fecundity with models of movement and empirical estimates of the prevalence of CWD to fit transmission characteristics to the population of deer in western Nebraska. We found that prevalence in western Nebraska over a 25-year simulation had a mean of 1.3% and CWD moved out from the endemic area at a rate of 49 km per year. We used the transmission characteristics in an individual-based model of CWD in eastern Nebraska and predicted that CWD would spread rapidly through the high-density population of deer. We used hierarchical generalized linear models with random spatial effects to model HD and CWD in Nebraska. We found that western and central Nebraska may have environmental factors that are favorable to midges that result in increased HD virus activity. We found that sampling bias may be increasing the uncertainty in estimates of prevalence of CWD in Nebraska. The results of our modeling efforts could be used to support changes in disease surveillance and harvest goals in Nebraska