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Effects of Roadway Traffic on Wild Ungulates: A Review of the Literature and Case Study of Elk in Arizona


Roads have been recognized as a threat to wildlife species for over 80 years. Studies on the effects of roads on ungulates species did not begin till the 1970’s. We identified 53 literature sources that suggested or examined traffic levels or road types and their effects on ungulate-vehicle collisions, ungulate distribution and roadway perme¬ability. Seventy-one percent of these suggested an effect of traffic level on ungulates. Only 47% of the papers suggested deer (Odocoileus spp.) were affected by traffic while in contrast studies on elk (Cervus elaphus) and moose (Alces alces) were at 84% and 82%, respectively. In studies that suggested no effect of traffic, other factors such as ungulate populations, ungulate behavior, driver behavior, and landscape variables were generally considered reasons for fluctuations in collisions. Although several studies examined ungulate distribution along roads, very few adequately looked at fluctuating traffic levels along highways. Highways have a greater potential for ungulate-vehicle collisions and are more likely to provide a barrier to ungulates than low traffic roads. Our further understanding of ungulate move¬ments and behavior in relationship to highways may be important in helping to mitigate ungulate-vehicle collisions and ungulate habitat fragmentation. Our State Route 260 project in central Arizona has provided a unique opportunity to examine elk movements in relation to traffic along a highway. We documented distinct shifts in distribution associated with fluctuating traffic levels as well as reductions in probabilities of at-grade crossings during increasing traffic levels. During the same study we found that increased traffic levels did not alter elk use of wildlife underpasses. Overall, properly designed wildlife underpasses and adequate funnel fencing adequately reduced elk-vehicle collisions while si¬multaneously promoting highway permeability during increasing traffic levels. Further research is needed to determine if these trends hold true for other ungulate species. Currently, research of fluctuating hourly traffic levels on ungulate behavior associated with highways is underway in Arizona, including American pronghorn (Antilocapra americana), mule deer (O. hemionus), Coues’ white-tailed deer (O. virginianus couseii) and further research on elk along highways with different geographical areas and traffic level ranges.

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