Mule Deer Highway Mortality in Northeastern Utah: An Analysis of Population-Level Impacts and a New Mitigative System

Rerouting highways to accommodate construction of the Jordanelle Reservoir in northeastern Utah caused a dramatic increase in vehicle collisions with mule deer (Odocoileus hemionus). I evaluated the effectiveness of a new system of highway crosswalk structures installed to reduce deer losses and preserve seasonal migrations. In addition, I constructed computer simulation models to investigate how highway mortality has impacted the Jordanelle deer population. The crosswalk system restricted deer crossings to specific, well-marked areas along highways where motorists could anticipate them. Subsequent to installation, mortality declined 42.3% and 36.8% along a four-lane and two-lane highway, respectively. I was unable to statistically demonstrate that observed mortality reductions were a direct result of the crosswalk system. The potential applicability of the structures, however, should not be dismissed. Reduced deer use of the highway right-of-way (ROW), the apparent maintenance of migratory behavior, and observations of animals crossing within crosswalk boundaries indicate the system warrants further testing. Lack of motorist response to crosswalk warning signs, the tendency for foraging deer to wander outside crosswalk boundaries, and the ineffectiveness of ROW escape gates contributed to most treatment area mortalities. I offer design modifications that address these shortcomings. Four years of field data revealed that highway mortality at Jordanelle was inversely density-dependent, removed between 5.6% and 17.4% of the population each year, and disproportionately impacted bucks. I incorporated this information into 3 competing simulation models in which highway losses operated in a strictly additive, partially compensatory, or strictly compensatory manner. The partial compensation model most closely tracked observed population dynamics, suggesting that highway losses were not completely offset by reductions in other mortality sources. Highway mortality apparently worsened a population crash initiated by severe winter conditions, and may be slowing the recovery. The disproportionate loss of bucks along roads altered sex ratios of simulated populations. Mitigative efforts should target road-kill reductions \u3e60% to avoid population declines predicted by the partial compensation model. Annual variation in demographic parameters offset the impacts of highway mortality at high population levels. At low population levels, however, highway mortality was severe enough to drive declining population trends