Managing an Overabundant Deer Population by Sterilization: Effects of Immigration, Stochasticity and the Capture Process

Fertility control is an alternative to lethal removal for managing overabundant populations. This approach invokes several simplifying assumptions; in particular, that specific individuals can be targeted for sterilization. We evaluated the influence of relaxing this assumption on the likelihood of achieving population control by considering potential sources of variation in the capture and sterilization process in an overabundant white-tailed deer (Odocoileus virginianus) population in Cayuga Heights, New York, USA. Using numerical analysis of an individually based seasonal projection model, including demographic stochasticity, we found that heterogeneity in both sampling, and response to trapping, increased the effort required to achieve population reduction within some acceptable degree of certainty. The inability to precisely control the demographic structure of captured deer required increased capture effort to achieve a given reduction. Trap-aversive behavior following capture improved the efficacy of sterilization while trap affinity reduced it. The efficacy of sterilization as a management tool was reduced dramatically by the presence of net immigration and emigration from the population. We found that sterilization could reduce growth rates of overabundant populations under some conditions, but it is unlikely to be a viable means for reducing populations in general, where there is significant net movement of individuals into the population, and where there is imprecise control over the capture process.