Spatiotemporal Breeding Strategies within a High Density, Male-skewed White-tailed Deer Population

Abstract

Animal movement is an integral part of most ecological, behavioral, or evolutionary processes observed in nature, and it has wide implications to numerous broad issues ranging from dispersal and migration to habitat fragmentation and probabilistic models of biological invasions. One facet of movement ecology revolves around optimal foraging and search theory – how do animals move through their environment and utilize the resources necessary for their survival. To quantify an animal’s search behavior, I developed a search intensity metric (SIM) that incorporated daily movement trajectories into a grid overlay of the study site (distance traveled/area encountered). Using the data’s variability between individuals to inform selection of an appropriate grid dimension, the SIM maximizes differences between individuals/groups but within populations. After providing 3 study cases to illustrate the SIM’s effectiveness and addressing how it differs from other metrics (e.g., fractal dimensions or tortuosity), I used it – in combination with other basic spatial metrics – to identify spatiotemporal breeding strategies employed by different age-class male white-tailed deer (N = 34) at Three Notch Wildlife Research Foundation in Bullock County, Alabama (2009–2011). With a male-skewed sex ratio and high density population, mature males concentrated their effort both temporally and spatially within the peak breeding period (and immediately thereafter during the post-breed season); conversely, juvenile and adult males exhibited roaming spatial behaviors likely due to displacement by more dominant rivals. Temporally, juvenile males focused reproductive effort before the other age classes in the population and possibly adopted “sneaker” strategies later in the breeding season. With a large sample of antlers (N = 487) from the same population, I examined factors affecting antler breakage and identified total number of points (positive relationship) and beam circumference (negative relationship) to be important predictors of antler breakage probability. Increased spongiosa within antlers (with greater mass) provided greater protection against breakage, whereas smaller-diameter antlers with many antler points experienced greatest breakage rates. In white-tailed deer males with significant bilateral asymmetry in antler structure, I examined 71 skulls (collected from across Alabama) from harvested white-tailed deer to assess probable cause for spike-on-one-side (SOOS) antler development. With increasing age of specimens, my likelihood of assigning probable cause (i.e., an injury to the skull and/or pedicle) increased (peaking at 76% in >3 year old males). Understanding how injuries to the antlerogenic periosteum allowed me to make age-specific recommendations for culling different age-class SOOS males. Finally, we investigated various aspects of maternal life history including senescence, fetal sex ratio allocation, and timing of conception by examining 1,355 reproductive tracts of female white-tailed deer in Alabama (1995–2011). Of several variables (maternal age/mass and litter size) evaluated, only days from average conception date was significant in predicting fetal sex ratio with daughters becoming more likely the further conceived from the peak breeding window. Maternal age and mass (as well as maternal age*mass interaction) influenced when a female was bred (conception timing) relative to the other females in the population (e.g., within younger age classes, larger females were more likely to conceive closer to the peak of conception than smaller females). Also, I found support for reproductive senescence which was previously undetected in white-tailed deer.