The potential of electrified barriers to keep black bears out of fenced road corridors at low volume access roads

Abstract

Fences can reduce wildlife-vehicle collisions, but it is not always possible to fence over long distances, especially not in multi-functional landscapes. Side roads, driveways, and the need for access to agricultural fields all result in gaps in the fence. In some cases, wildlife guards or gates are installed at access points. However, gates usually require people to get in and out of their vehicle and they are often left open. Wildlife guards are typically only suited for low traffic speed, and while they can be a substantial barrier to ungulates, they are readily crossed by species with paws, including bears. Electrified barriers embedded in travel lanes can be a substantial barrier to both ungulates and bear species and while they can be suitable for higher traffic volume and speed, the costs are typically higher than for low volume and low speed roads. We explored the potential of low-cost electrified barriers to keep bears from accessing fenced road corridors at low traffic volume and low speed vehicle access points. As a first step, we conducted the study on private land at a melon patch that was a known attractant for black bears. We investigated the effectiveness of an electric fence and 5 different types of electrified barriers designed to keep black bears out of the melon patch. The electrified barriers included a swing gate, a standard bump-gate, a modified bump-gate with conductive netting, drive-over wires a few inches above the ground, and a drive-over mat. Trail cameras were installed at each access point to document approaching black bears and potential crossings into the melon patch. The swing gate, modified bump-gate, drive-over wires, and drive-over mat were an absolute (100%) or near absolute barrier (94.3%) for black bears while the standard bump-gate was a poor barrier (48.4%). Through a step-by-step process, the weak points of the electrified barriers at the vehicle access points and the electric fence around the melon patch were addressed. After addressing a weak point at a vehicle access point, the bears increasingly dug under the fence to enter the melon patch. However, eventually the melon patch became almost inaccessible to black bears. The number of black bears trying and succeeding to enter the melon patch at a particular location depended on how difficult it was to enter at other locations. This illustrates that fences and vehicle access points should be designed, operated, maintained, and monitored as a system rather than as individual features, regardless of whether the goal is to protect crops or to keep animals out of a fenced road corridor. The total number of black bear observations at the locations monitored with a trail camera, regardless of which side of the fence or electrified barriers the bears were on, was 95% lower in 2021 than in 2020. Combined with having no indication of a substantial drop in black bear population size from 2020 to 2021, this suggests that after the black bears were no longer able to enter the melon patch, they drastically reduced their presence in the immediate surroundings and reduced their effort to try and access the crop; the attraction of the melon patch and the habit of eating its melons was broken.