Each wildlife species, ranging from small-sized to large-sized, requires different environmental factors to be present in order to successfully travel from one area to another (wildlife movement). While some animal species need light (diurnal) to travel, others prefer to travel in the dark (nocturnal), and can utilize a dark tunnel, or other structure, if it is available.
In recent history, the use and the benefit of wildlife crossings was not taken into consideration during the planning phase for the construction of new roads. An example of this is U.S. Route 101in Los Angeles. This freeway goes from the City (Downtown Los Angeles) to Ventura County (along the coast). The 101 separates two mountain ranges: the Santa Monica Mountains and the Santa Susanna Mountains, that connect to Los Padres National Forest. These mountain ranges contain most of the wildlife within the region. Specifically, the wildlife finds it difficult to cross highways due to lack of wildlife crossings within the area. Wildlife are forced to use transportation structures such as culverts, pipes, and drainages as a substitute for wildlife crossings, if necessary. The effects of impeded crossings on this highway has caused a lack of genetic diversity among the mountain lion and bobcat, as well as road kills and injuries. To solve these problems a wildlife crossing must be built.
Wildlife crossing structures are designed to increase permeability and habitat connectivity across roads. These structures also reduce motor vehicle collisions with wildlife, consequently reducing the likelihood of injury to persons or damage to motor vehicles. Wildlife crossing structures include underpass tunnels, viaducts, overpasses, amphibian tunnels and culverts. Caltrans and its stakeholders have determined that a wildlife crossing is necessary at Liberty Canyon and the 101 Freeway in the City of Agoura Hills. This will allow wildlife from the southwestern portion of the Santa Monica Mountains to increase genetic variability and to avoid road kills by crossing to the northeastern portion of the mountains, continuing to the Santa Susanna Mountains and Los Padres National Forest. The right wildlife crossing will not only serve pumas and bobcats, but it will also serve other target species such as coyote, Western fence lizard, mule deer, woodrat, wrentit, and western toad.
The constraints for this area (U.S. Route 101), which can also be true for most of the freeways in Southern California include:
1.No new projects proposed that can fund the wildlife crossing improvements
2.Lack of qualitative and quantitative collision data in the area to justify the need for the wildlife crossing and to secure Federal Highway Authority funding
3.Fear from motorists to report collision ("Oh no, I killed a big cat or deer!")
4.Southern California natural disasters such as wild fires and earthquakes
6. Wildfires and fear of big cats and the fear of big cats.