BEHAVIORAL-RESPONSE OF FREE-RANGING ELK TREATED WITH AN IMMUNOCONTRACEPTIVE VACCINE

Most wildlife contraceptive studies to date have evaluated treatment e fficacy on individuals, but little research has evaluated the potentia l behavioral effects associated with inhibiting conception in polyestr ous species. During autumn 1993 and 1994, we compared the behavior of 10 free-ranging, radiocollared cow elk (Cervus elaphus) vaccinated wit h porcine zona pellucida (PZP) immunocontraceptive vaccine with 10 unv accinated cow elk. We tested the hypothesis that breeding behavior wou ld be prolonged in PZP-treated cows due to repeated estrus cycling. Se xual interaction rates of treatment and control cows were similar duri ng the normal breeding season (P = 0.96) but differed significantly du ring the postbreeding season (P < 0.001), when almost no sexual intera ctions were observed in control cows. Postbreeding season interaction rates in treated cows remained at the level observed during the breedi ng season. We did not detect any significant changes in activity patte rns or social structure of the elk during the postbreeding season as a consequence of the apparent PZP-induced cycling (P > 0.50). It is unc ertain whether the results of this study apply to possible effects of PZP treatment for management-level applications where a large proporti on of the females would be treated. We recommend population-level expe riments to further our understanding of the effects of contraceptive t echnologies on the behavior and dynamics of free-ranging ungulate herd s.