Wildlife guards (WG) are intended to deter wildlife from entering the road while wildlife crossing structures (WCS) are designed to give wildlife safe passage under the road. These mitigation structures have been installed on State Highway (SH) 100 and farm-to-market (FM) 106 to mitigate ocelot (Leopardus pardalis) mortalities in Cameron County, Texas. To determine the effectiveness of these wildlife mitigation structures in decreasing wildlife-vehicle collisions, we used motion triggered and external infrared trip wire triggered camera traps. Camera traps are commonly used to monitor medium to large mammals, but few studies have assessed their effectiveness for monitoring smaller species. Our objective was to determine if ground level infrared trip wire heights at WCS and WG would capture small mammals and herpetofauna that may be missed by standard infrared trip wire heights set for mesocarnivores. We hypothesized that ground level trip wire positions would capture fewer medium-sized species and a greater number of small mammals and herpetofauna compared to standard trip wire heights. Reconyx HyperFire 2 cameras connected to external infrared trip wire systems were installed at two heights (standard and ground) on five WCS on FM 106 and five WG on SH 100. The standard trip heights at WCS were higher (23.4 + 1.5 cm) than WG (10.7 + 0.94 cm); all ground level trips were zero as they are placed directly on the ground. The wildlife communities between trip heights were different at WCS (P ≤ 0.001) but not different at WG (P = 0.321). Rodents, Virginia opossums, birds, and nine-banded armadillos had higher detections on the ground trips while northern raccoons had higher detections on the standard trip heights at WCS. These five species contributed to 72.65% of the dissimilarity between the wildlife communities at WCS captured on standard and ground trip heights. At WCS, ground trips captured all amphibian events (n=30) and most reptiles events (96.3%, n=82), which also had fewer ghost triggers in general than the standard trips except during rain events. Ground level trips were successful in capturing a greater number of small mammals and herpetofauna than standard trip heights and also captured 66% more medium-sized mammals (n=1,588) than standard trip heights (n=956) at WCS. Other published camera trapping methods targeting herpetofauna and small mammals require funneling or baiting. While the objective of the design used here was for monitoring wildlife mitigation structures, which themselves serve as a funnel, it could be applied in any environment where animals are known to cross (e.g., game trails, burrow entrances). A lower external infrared trip height would be beneficial to managers assessing WCS use by state or federally threatened rodents and herpetofauna, while not sacrificing monitoring efforts of mesocarnivores, such as the ocelot.
wildlife mitigation structures