Road ecology blog: Mitigation measures for bighorn sheep, near Thompson Falls, Montana, USA. This section of Hwy 200 needed to be reconstructed and mitigation measures to reduce collisions with bighorn sheep were made an integral component of the project. Advise on the types of mitigation measures and their configuration are detailed in this report:
Huijser, M.P. & A.P. Clevenger. 2013. Review of proposed bighorn sheep mitigation measures along montana Hwy 200, East of Thompsonfalls, Montana. Western Transportation Institute, College of Engineering, Montana State University, P.O. Box 174250. Bozeman, MT 59717-4250, USA.
Images below: the reconstructed bridge across the Thompson river. This bridge is also suitable for bighorn sheep (Ovis canadensis) to pass under.
Image below: The wildlife fencing east of the bridge. The first phase of the project included the reconstruction of the bridge and a relatively short road section just east of the bridge. In a later phase a second underpass will be constructed, specifically for bighorn sheep and other wildlife. Erecting a 2.4 (8 ft) fence without fence-end treatments to discourage animals from walking into the fenced road corridor would have resulted in a dangerous situation for both drivers and wildlife. On the other hand, the wildlife fence needed to be constructed as part of the first phase because of budget allocation and project delineation. Therefore the tall fence posts (2.4 m (8ft)) with low right-of-way fence (about 1.2 m (4 ft)) were installed in phase 1 (see image below). Once the wildlife underpass has been constructed further to the east, and once the wildlife fences are extended further to the east (with potential fence-end treatment), the height of the wildlife fence will be increased to 2.4 m (8 ft). This will be as simple as attaching another roll of mesh wire fence to the existing tall posts. See the report referenced above for more details.
Image below: There are a number of drive ways and access roads in the area. Wildlife guards (similar to cattle guards) and gates were provided.
Image below: It is important that the wildlife fence has a tight connection to the wildlife guard. In the image below we see that there is too much space between the fence and the wildlife guard. This may allow animals to walk in between the fence and the metal bars and access the fenced road corridor. It is advisable to retrofit this situation.
Image below: this is a better situation; a tight connection of the fence to the metal bars of the wildlife guard.
Images below: Wildlife jump-outs or escape ramps allow the animals to escape from the fenced road corridor. The earthen ramps allow the animals to walk up to the height of the fence and then jump down to the safe side of the fence. Wildlife jump-outs should be low enough to allow animals to jump down, but they should be high enough so that animals will not jump up into the fenced road corridor.
Image below: The purpose of the bar (horizontal wooden post) is to increase the height of the jump-out for animals that want to jump up (undesirable) into the fenced road corridor; they would not only have to clear the retaining wall but also the wooden bar. On the other hand, animals that want to jump down (desirable) can simply step over the wooden bar before jumping down. Thus the wooden bar is aimed at influencing the ratio of animals jumping up vs. down.
Image below: The retaining wall of the jump-outs has "ledges". This may allow certain animal species to climb up the wall (undesirable). Bighorn sheep are adept at jumping and climbing steep rocky slopes. Thus this type of retaining wall may not be the best for bighorn sheep; a smooth retaining wall would have been preferable.
Click here for images of wildlife fencing.
Click here for more images of wildlife jump-outs or escape ramps.
Click here for other images of wildlife guards, cattle guards, electric mats or gates.
Click here for images of wildlife underpasses.
Click here for more images of long bridges or viaducts.
Click here for images of multifunctional underpasses.
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