Effects of Fertility Control on the Movement Ecology of White-Tailed Deer

This doctoral thesis explores the effects of fertility control on the movement ecology of white-tailed deer (Odocoileus virginianus Zimmermann). Deer populations may become abundant in human-dominated landscapes, taking advantage of anthropogenic resources and the lack of natural predators. This abundance poses increasing ecological, economic, and social challenges globally. As human activities expand, conflicts between deer populations and human interests intensify, manifesting in issues such as deer-vehicle collisions (DVCs), the spread of tick-borne illnesses, and habitat degradation. While traditional population control methods, such as controlled hunting, have proven effective, they are often impractical in suburban and urban settings. Non-lethal fertility control methods, including vasectomy, ovariectomy, and immunocontraceptive vaccines, present alternative solutions that may circumvent the need for lethal management. However, these methods induce physiological changes that may alter movement behavior. This thesis aims to bridge the knowledge gap concerning how fertility control interventions impact the movement behavior of white-tailed deer. Chapter 2 lays the groundwork by addressing a critical methodological issue often overlooked in studies of ecological movement responses — specifically, the relationship between mean speeds and diffusion rates using continuous-time speed and distance estimation techniques. Accurate modeling of an animal’s speed and distance traveled can be critical for interpreting behavior, yet ecological data often are too coarse, or the location error is too great to resolve these measures. Diffusion rates, in contrast, can be estimated using continuous-time models at even coarser sampling intervals. To examine this relationship, a regression analysis was conducted to estimate the correlation between mean speed and diffusion rate, accounting for uncertainties in both variables. Results indicated a strong, sublinear correlation between mean speed and diffusion rate, with a 1% increase in diffusion rate in my focal species predicting a 0.40% increase in mean speed (99% CI: 0.38–0.42%). Sampling intervals were progressively coarsened to assess the robustness of these estimates, and simulations were run using known true values to further evaluate the relationships. Across all sampling intervals, diffusion rates consistently remained substantially more accurate and precise than mean speed estimates, even when speed estimation was not possible. These findings establish diffusion rates as a more reliable and robust metric for linking movement to behavior across a wider range of datasets, thereby providing a foundation for the subsequent analyses of fertility control effects on deer movement in Chapters 3 and 4. Chapter 3 evaluates the effects of a large-scale vasectomy program on the movement behavior and activity of free-ranging white-tailed deer. This study leverages an existing fertility control program implemented on Staten Island, New York, USA, where vasectomies were performed on over 97% of antlered males, resulting in a dramatic reduction in fawning (approximately 95%). This intervention effectively left most female deer unbred, leading to multiple estrous cycles throughout the breeding season. Concerns have been raised that the additional estrus periods may extend breeding activity, potentially leading to decreased body condition and increased incidence of DVCs. To investigate these potential consequences, biologging devices were deployed on a total of 158 deer, across two sites: the treatment site on Staten Island and a control site at Rockefeller State Park Preserve in Pleasantville, NY, USA. The dataset included global positioning system (GPS) and accelerometry data from 84 females and 40 males. Advanced analytical methods, including continuous-time movement models and Hierarchical Generalized Additive Models (HGAMs), were applied to assess deviations in space use, movement patterns, and activity levels between treated and untreated groups. The results indicate that, contrary to initial concerns, the vasectomy program did not induce behavioral or social changes likely to negatively affect population health or safety during the study period. Chapter 4 investigates the effects of ovariectomy, an alternative fertility control method, on female white-tailed deer movement behavior. Ovariectomy induces anestrus, thereby preventing treated females from entering estrus, and eliminating estrous cycles and associated behaviors. Concerns have been raised that the absence of reproductive behavior could lead to altered movement patterns that might negatively impact body condition or increase the likelihood of DVCs. This chapter employs a treatment-control design using IoT-based telemetry data from 20 free-ranging female deer who were part of a management program in South Euclid, Ohio, USA. Ten individuals had undergone ovariectomy, while the remaining ten served as untreated controls. To assess the impact of ovariectomy on movement ecology, a 7-day moving window approach was applied to analyze diffusion rates, home-range size, and excursivity. Consistent with the findings from Chapter 3, the analysis revealed no significant differences in movement behavior between the treated and control groups, suggesting that ovariectomy does not introduce behavioral risks that would exacerbate management concerns. The findings from this thesis provide substantial evidence that fertility control methods, specifically vasectomy and ovariectomy, do not induce significant changes in the movement behavior of white-tailed deer at the time scales investigated. These results support the viability of non-lethal fertility control as a management strategy for addressing abundant deer populations in urban and suburban environments. By ensuring that such methods do not lead to unintended behavioral consequences, this work contributes to the development of new approaches to wildlife management in human-dominated landscapes.