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Assessing changes in clusters of wildlife road mortalities after the construction wildlife mitigation structures

Citation

Yamashita, Thomas et al. (2022), Assessing changes in clusters of wildlife road mortalities after the construction wildlife mitigation structures, Dryad, Dataset, https://doi.org/10.5061/dryad.qnk98sfhb

Abstract

Collisions with vehicles can be a major threat to wildlife populations, so wildlife mitigation structures, including exclusionary fencing and wildlife crossings, are often constructed. To assess mitigation structure effectiveness, it is useful to compare wildlife road mortalities (WRMs) before, during, and after mitigation structure construction; however, differences in survey methodologies may make comparisons of counts impractical. Location-based cluster analyses provide a means to assess how WRM spatial patterns have changed over time. We collected WRM data between 2015 and 2019 on State Highway 100 in Texas, USA. Five wildlife crossings and exclusionary fencing, were installed in this area between Sep 2016 and May 2018 for the endangered ocelot (Leopardus pardalis) and other similarly sized mammals. Roads intersecting State Highway 100 were mitigated by gates, wildlife guards, and wing walls. However, these structures may have provided wildlife access to the highway. We combined local hot spot analysis and time series analysis to assess how WRM cluster intensity changed after mitigation structure construction at fine spatial and temporal scales and generalized linear regression to assess how gaps in fencing and landcover were related to WRM cluster intensity in the before, during, and after construction periods. Overall, WRMs/survey day decreased after mitigation structure construction and most hot spots occurred where there were more fence gaps, and, while cluster intensity increased in a few locations, these were not at fence gaps. Cluster intensity of WRMs increased when nearer to fence gaps in naturally vegetated areas, especially forested areas, and decreased nearer to fence gaps in areas with less natural vegetation. We recommend that if fence gaps are necessary in forested areas, less permeable mitigation structures, such as gates should be used. Local hot spot analysis, coupled with time series and regression techniques, can effectively assess how WRM clustering changes over time.

Methods

Regular wildlife road mortality surveys of mammals grouped into 100-m segments to examine how clustering changed with construction of wildlife mtigation structures. Local hot spot analysis was run on 13 time blocks using ArcMap 10.6.

Usage Notes

This dataset includes counts of mortalities, hot spot z-scores and p-values for each of the time blocks used in the study.

Funding

Texas Department of Transportation, Award: 57-9XXIA001