Exploring Mitigation Options to Reduce Vehicle-caused Mortality for the Oregon Silverspot Butterfly, Speyeria zerene hippolyta, along Highway 101 at the Siuslaw National Forest

摘要

The Oregon Silverspot Butterfly (OSB), Speyeria zerene hippolyta, is federally listed as “threatened.” It historically inhabited coastal regions of Washington, Oregon, and California (USFWS 2001). OSB populations only remain at five sites, four of which are in Oregon; one remaining population is in California, and none exist in Washington state as they have been extirpated (BFCI 2009; USFWS 2001). The site selected for this study was Rock Creek-Big Creek, adjacent to the Siuslaw National Forest (Figure 1) (Appendix 1). At this site OSB habitat is bisected by Highway 101; butterflies are observed to use both sides of the highway throughout their life cycle (P. Hammond, personal communication, June 12, 2009). It is suspected that vehicles on Highway 101, through collisions and their turbulence, present a substantial threat to OSBs at this site. This suspicion, however, has not yet been quantified and is only minimally evaluated in this paper.Effective mitigation techniques have rarely been developed and tested for small or flying organisms (but see, e.g., Smith 2009, Bard et al. 2002). Mitigation for one species may not work effectively for others (e.g., Jackson and Griffin 2000). Moreover, due to expense and scale, it is prohibitive to test multiple mitigation options sequentially. Therefore, we explored whether gathering targeted ecological data would help prioritize mitigation options for a threatened species, the Oregon silverspot butterfly (Speyeria zerene hippolyta, hereafter, OSB). We studied OSB ecology in order to evaluate the likely success of mitigation options before funding was pursued for implementing or directly testing any of them.In this research, we considered four potential management options that seemed most likely to be effective based on available information, including barrier installation; earthen berm removal and other actions to reduce the attractiveness of the road relative to the surrounding habitat; environmentally triggered, flashing speed-reduction-sign installation; and vegetation manipulation. Again, because these management scenarios are not yet in play, we could not directly test them. Rather, we gathered data on the behavioral ecology of OSBs and the environmental conditions of the road compared to surrounding habitat to determine which mitigation measures would have the greatest potential for effectiveness. To inform mitigation options we examined six questions about environmental conditions across habitats or microhabitats and how these correlated with OSB presence.