Wildlife Crossing: using culverts to assist wildlife from one habitat to the next  

The growing human population is a global problem shared throughout the world. Much of human activity includes expansion and development in pristine habitats that are needed for the survival of many endangered and non-endangered species. One of the most common effects of development is the fragmentation of habitat by roads which leads to a lack of landscape connectivity. Animals need habitat to be connected for movement between surrounding areas to perform natural behaviors such as hunting/foraging, mating, and for dispersal. Animals have had to change their method of dispersal and cross to surrounding habitats by crossing roads.

Unfortunately in many circumstances this leads to death of many wildlife species. Wildlife roadkill has become an extremely common sight in our everyday lives. It is hard to think of a day that I drive without seeing some type of animal that has been hit by a car on the side of the road. These sightings will become much more common as the human population continues to grow. As biologists, seeing dead wildlife on the roads is very frustrating, but fortunately there is a way to help all animals cross roads safely.

Wildlife crossings are a relatively new idea and have been used by several countries including the U.S. to combat the amount of wildlife deaths that occur on busy roads. A wildlife crossing can be a bridge, tunnel, culvert, canopy, slide, etc., that allows animals to cross to surrounding habitats that they would have been able to get to if there was not a road blocking their way. Although this isn’t their natural path to move between habitats, it still allows them to go back and forth without threat of a vehicle strike.

Among all animal taxa, mammals are hit by cars the most. One mammal in particular is the reason that our small mammal group wanted to test a set of wildlife crossings in Southern California. The San Bernardino kangaroo rat (SBKR) is an endangered rodent species that is native to parts of San Bernardino and Riverside County. Their numbers dropped mainly due to habitat loss from surrounding development. In areas that they still exist, it is critical that we do as much as we can to enhance the habitat that still remains.

There are four culverts that were built under a road to give kangaroo rats the ability to cross to adjacent habitats safely. The culvert crossings are 60 feet long, 6 feet wide and 2 feet tall. We enhanced 2 of the 4 culverts with plant cover and added seeds to try and help facilitate their movement through the entire length. The great part about these culverts is that they are equipped with 5 wildlife game cameras, 2 at each opening and 1 in the middle. We put these cameras throughout to let us see if the kangaroo rats were using them. Once a month I get to crawl through these culverts, sometimes through mud, to retrieve all of the SD cards in the cameras. The best part of this job comes next: seeing what used the culverts the previous month!

Over 84 weeks of monitoring these culverts, there have been no pictures of SBKR in any of the culverts. This could be because they are not in the area and therefore not using the culverts to cross.

The great news is that there have been hundreds of visits from several other animals from mammals, birds, reptiles, and amphibians. Desert cottontails are the number one species that use the culverts the most. Other animals include: brush rabbits, ground squirrels, spiny furred pocketmice, deer mice, woodrats, coyote pups, bobcats, skunks, opossums, raccoons, toads, lizards, towhees, wrens, burrowing owls, sparrows, thrashers, quail families, doves, roadrunners and more.

A lot of these animals are using the entire length of the culvert and crossing from one habitat to the next without stepping on the road at all, which is truly incredible!

Wildlife crossings are a very simple idea and will become an asset to our changing environment. When I see how well these culverts have worked it makes me feel hopeful that animals can and will use these crossings in high traffic areas.





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