Deer–vehicle collision trends at a suburban immunocontraception site

Observations of extended estrus seasons in female white-tailed deer (Odocoileus virginianus) vaccinated with porcine zona pellucida (PZP) immunocontraceptives have led to speculation that management use of PZP would, perversely, increase the rate of deer–vehicle collisions. To test this hypothesis, we studied PZP-treated female deer at the National Institute of Standards and Technology, Gaithersburg, Maryland. PZP-treated female deer did not differ from untreated female deer in risk of death by vehicle collision, and the number of deer killed in vehicle collisions was uncorrelated with the number of deer treated with PZP, whether or not population size was controlled for. The reduction in deer population size observed during PZP applications was associated with a reduced frequency of deer–vehicle collisions. Our results suggest that any added collision risk caused by behavioral effects of PZP is unmeasurably small compared to the effects of population management and other mitigation actions.