Evaluating Structure Class and Construction Effects on Wildlife Use of Road Underpasses
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Road ecology, the study of ecological impacts of roads, has become a major area of research. Road ecology involves the study of a variety of road effects such as soil erosion, hydrological effects, soil chemistry alterations, direct road mortality, and consequences to wildlife at the local and population level. This study aims to assess wildlife interactions between two classes of road underpasses (bridges and culverts) and looks into the effect of road construction in the area during the observation period. Six road underpasses were monitored on a 24 km stretch of bifurcated highway US 281, 4 km south of George West, Texas, within the South Texas Brush Country near the Bordas Scarp. Two types of established underpasses were monitored: bridge (n=3) and culvert (n=3). Camera arrays were installed at each underpass to maximize the detection of wildlife utilizing or interacting within the corridors of the underpass as well as the surrounding road-effect zone habitat. Linear mixed-effects models were used to analyze the effects of construction disturbance and underpass class between the two data sets where time intervals between independent captures responded to pre- and postdisturbance and bridge and culvert classes, respectively. Between the dates monitored, 10 June 2017 to 6 July 2019, a total of 2,111 independent captures events were observed, 950 prior to the disturbance and 1,161 afterwards from the two disturbed bridge stations. Between the dates monitored 10 June 2017 to 23 May 2018, a total of 4,940 independent captures events were observed, 2,301 under bridge structures and 2,639 under culverts at 6 monitored stations. Our findings suggest that neither disturbance under bridges nor structure type affected use by the wildlife population detected using these underpasses; however, we did see differential use among species. Post-construction monitoring studies, such as this one, can shed light on the effectiveness of these road underpasses as mitigation measures and can also provide information about how an existing road could be altered to achieve similar results.