Imagine you have excellent eyes, excellent hearing, and excellent predator avoidance skills. You see a moving animal that is not your friend and you take a little time to judge its nearness, its speed of travel, and you move away, avoiding becoming its next meal. Now imagine the predator is suddenly on top of you and you don’t know how it ran so fast to get there. The predator somehow moved from there to you at a speed you have no experience with. You are its next meal.
That’s what happens to migratory mule deer or elk on a highway. Deer and elk must cross highways to get to summer range in spring, and then cross again to get to their winter range in fall. They must try to judge a metal-and-rubber predator, and they often lose.
In a study of deer-vehicle collisions (DVC) on Oregon highways 97 and 31 in central Oregon from 2005-2010 by Oregon Department of Fish and Wildlife research staff, it was found that most DVCs (67%) occurred during spring or autumn migration. Mule deer used the same migration routes year after year, and these routes typically merged across highways. In addition, DVC density (the density of deer-vehicle collisions over time) was strongly related to where migration routes crossed Highways 97 and 30 in south central Oregon. Helpfully, for engineers attempting to reduce DVCs, it was found that migration routes were the strongest predictor of DVCs, more than landscape features such as tree cover, water routes, topography, development, or traffic counts. I say “helpfully” because this meant that deciding where to put crossing structures on a highways may be as simple as locating migration routes or high DVC density.
Researchers also found that about the same number of deer succumbed to vehicles as to predators, about 10%. Interestingly, predator control is popular in rural counties where people believe that cougars or wolves take out too many deer and elk, leaving too few to hunt. But reducing DVCs is a straight-forward and highly successful alternative to predator control.
Oregon is behind other states in constructing wildlife crossings. Now a recently passed bill in the Oregon legislature will allocate $7 million from the general fund for safe wildlife crossing structures, and this funding may serve as a match for even more federal funding. At a time when infrastructure dollars are being allocated to states, this is timely legislation that will help prioritize how to use these dollars.