The use of wildlife underpasses and the barrier effect of wildlife guards for deer and black bear

The reconstruction of 90.6 km of U.S. Highway 93 from Evaro to Polson, MT on the Flathead Indian Reservation includes 41 fish and wildlife crossing structures and 13.4 km of road with wildlife fencing. These measures are aimed at reducing wildlife–vehicle collisions and increasing human safety, while allowing wildlife to traverse the landscape. In the fenced road sections, gaps for side roads are mitigated by wildlife guards (similar to cattle guards). We focused on a 1-km fenced section where animals can either cross the road using 5 crossing structures (4 culverts and 1 bridge), or they can access the road through two guards on the east side of the road. Wildlife movements were monitored with cameras at the two guards and in one large crossing structure adjacent to one of the guards. We investigated how effective these guards were as a barrier to deer (Odocoileus sp.). We also compared movements across the guards to those through the crossing structures. The guards were 85% or more effective in keeping deer from accessing the road, and 93.5% of deer used the crossing structure instead of an adjacent guard when crossing the road. Though the guards were not an absolute barrier to deer, the results indicate deer were substantially discouraged from crossing the guards, and the vast majority crossed the road using the crossing structure rather than the guard, indicating the guards are an effective means of mitigation. Introduction Fencing can significantly reduce ungulate access to the road corridor (Falk et al. 1978) and has been shown to reduce wildlife–vehicle collisions by ≥79% (Reed et al. 1982, Clevenger et al. 2001, Dodd et al. 2007). However, in developed areas, gaps in fences are necessary to allow vehicles access to and from main roadways. Without additional measures, gaps can allow wildlife to enter the fenced road corridor. While gates (locked or unlocked) have been used at low use side roads, they are sometimes left open and are 12 not suitable for higher traffic volumes. In contrast, wildlife guards appear to be a strong barrier and also address higher traffic volumes. Traditional cattle guards have been used and reported effective for white-tailed deer (Odocoileus virginianus) under some circumstances (Bashore and Bellis 1982, Belant et al. 1998). However, to be suitable for public roads and effectively exclude wildlife from the fenced road corridor, several factors must be considered. Standard cattle guards may not be safe for pedestrians, cyclists, and heavy vehicles, so alternative designs may be required (Peterson et al. 2003). In addition, side panels (fencing) should be extended the full length of the guard to prevent diagonal (shorter) crossing by wildlife (Sebesta et al. 2003). Guards should also be placed over a pit with walls (e.g. concrete) or raised in another manner to prevent wildlife from crossing by placing their feet on the ground between the grates (Sebesta et al. 2003). In this field study, our objective was to investigate how effective a particular type of wildlife guard design was as a barrier to mule deer (O. hemionus) and white-tailed deer movement and, therefore, how effective it was in keeping deer from accessing the rightof-way along a fenced section of U.S. Highway 93. Study Area From October 2004 through November 2010, there were eight reconstruction projects along 90.6 kilometers of U.S. Highway 93 from Evaro to Polson, Montana located on the Flathead Indian Reservation. The project corridor is now the site of one of the most extensive wildlife crossing mitigation projects in North America, both in terms of road length and the number of fish and wildlife crossing structures, 41 total (excluding likely 13 future mitigation measures in the Ninepipes area). In addition to crossing structures that allow animals to cross under or over the road safely, the reconstruction included 2.4-m high wildlife exclusion fencing along some road sections intended to restrict access of wildlife to the road corridor. The Flathead Indian Reservation is home to the Confederated Salish and Kootenai Tribes, which includes Bitterroot Salish, Pend d’Oreille and Kootenai tribes. U.S. Highway 93 runs north-south through the reservation and is in the process of being reconstructed to improve safety and allow for higher traffic volume. This study was conducted in a road section where the road reconstruction was completed in 2006. This section is referred to as “Ravalli Curves” and is located just south of Ravalli and the junction with MT Highway 200. Along with the reconstruction of the actual road, wildlife fencing, wildlife underpasses, jump-outs, and wildlife guards were built along a 1.0-km section just south of Ravalli, MT (Figure 6). The wildlife underpasses varied in type and size. There were three medium mammal culverts (about 1.2–2.8 m wide, 1.2–1.6 m high), one large mammal underpass (about 7.7 m wide, 3.5 m high), and one bridge (about 28.4 m wide, 3.9 m high) (Table 1.). There were also two wildlife guards and 9 jump-outs in the study area. Jump-outs are earthen ramps that allow animals that may have entered the fenced road corridor to jump down to safety. Jump-outs should be low enough so that animals will readily jump out of the fenced road corridor but high enough to discourage animals from jumping in. The two wildlife guards had a jump-out on the other side of the road. If an animal crossed the wildlife guard into the fenced road corridor, the jump-out on the other side allowed it to cross the road and escape to safety. 14 The landscape adjacent to this 1.0-km section of mitigation measures was rather homogeneous, with a railroad and the Jocko River running parallel to the road on the west side, an old oxbow of the Jocko River to the east, and steep hills to both the east and west. The surrounding vegetation was primarily coniferous forest, with some grassland, as well as riparian habitat along the river and old oxbow. Average minimum temperatures ranged from -8.20 C in winter to 9.80 C in summer, and average maximum temperatures ranged from 0.70 C in winter to 29.10 C in summer. Temperatures ranged from well below -180 C to over 380 C. Average annual precipitation was 403.4 mm, with precipitation mostly in the form of snow in the fall, winter, and spring and mostly rain in the summer. (NRCS 2005)