Dr. Nicki Frey: Wildlife crossings
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The federal government is allocating $350 million for the construction of bridges and tunnels that allow animals safe passage over or under roads.
On April 16, 2024, SciLine interviewed: Dr. Nicki Frey, an associate extension professor of wildlife biology at Southern Utah University. See the footage and transcript from the interview below, or select ‘Contents’ on the left to skip to specific questions.
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Introduction
[0:00:19]
NICKI FREY: Hi. I’m Nicki Frey, and I am an extension wildlife professor at Utah State University. And I study a field called human wildlife conflicts. And that means that I don’t really specialize in any one animal, but I specialize in the relationship between humans and the wildlife that live around them. And ways that we can resolve conflicts between the two so that we can appreciate wildlife more. So, if we can understand wildlife and what they’re doing and how they do things, then maybe we could appreciate them more. And then when we do appreciate them, but there are still conflicts, I can help the people resolve those conflicts ethically.
Interview with SciLine
Based on the available data, how many animals are hit by cars each year in the United States?
[0:01:09]
NICKI FREY: We can only get these estimates from instances where there are collisions, and those collisions are reported to the insurance companies. But in the most recent insurance company reports, we’re estimating 2 million collisions a year. And those are only on large bodied animals. So, think about deer or elk or sheep—those large bodied animals. And we can easily estimate another 2 million animals—or 2 million collisions—for things that don’t get reported, like a skunk or a raccoon or squirrel or even a frog. So, quite a few animals are killed each year. And to put that into context, in the state of Utah alone, more deer are killed by wildlife vehicle collisions than are killed by hunters annually.
Can you quantify the number of deaths and injuries and the amount of property damage attributed to cars colliding with wildlife each year?
[0:02:15]
NICKI FREY: For humans, we estimate about 200 lethal collisions happen annually, and about 26,000 serious injuries happen annually, at a cost of about 8 billion dollars.
How do roads interfere with the lives of animals?
[0:02:35]
NICKI FREY: Roadways can really interfere with how animals can move through the environment. And animals move through the environment for several reasons. Sometimes it’s just part of their daily movements just to try to get to water or to try to get food. We also have animals that migrate seasonally. So, the more common animals that do that will be deer, elk, bighorn sheep—some of those larger animals that are implicated in collisions. And they’re migrating to summer range where they can get food and maybe get away from the heat. And then they’ll move to what we call winter range, where they can avoid snow, still find some food, etc. So, if you have a road that bisects that winter range and that summer range, the animals can perish just trying to get there. And if they can’t get there, then they’re going to either lose their lives through starvation, or they can lose their health. And if their health declines, then that inhibits their ability to reproduce successfully and to rear offspring. So, that’s just migration. We also have animals that move through a process called dispersal. And they’re getting out of their birth home range—so away from mom or away from mom and dad—to have a better genetic reproduction. So, they don’t want to reproduce with the animals that they’re related to. So, they need to disperse out of that home range for genetic health. And if we don’t have that dispersal, then we start having what we call genetic bottlenecks, where the animals can become inbred. And we see a lot more mutations or a lot more undesired characteristics and lowered health in that population. So, those are the kind of the two big issues and then we have a third one that’s just competition. And that happens every year. And animals try to move out from areas where there’s high density into areas where there’s low density so that they can find better food or find better shelter or find more mates without having to compete. So, if they can’t do that, then we do have this increased competition and those animals can lose their lives through the competition process. So overall, we just have a net loss of wildlife health and wildlife populations when we have roads bisecting their habitat like that.
What are wildlife crossings?
[0:05:09]
NICKI FREY: Wildlife crossings are really any structure that’s designed to allow animals to move across highways or railroads or some sort of human infrastructure to get from point A to point B, whether that’s for competition or for migration. So, there’s a lot of different kinds of wildlife crossings. So, we have things called culverts and culverts can be anything from like a drainage pipe that goes under a small road that allows frogs and salamanders to cross. We also have large culverts that allow mule deer to cross under big highways, so that anything that goes under the highway would be a culvert. We also have crossings called viaducts, and they’re just that passage that goes under maybe a large bridge or a large trestle roadway, so the animals can pass freely under that roadway, it’s very big. And then the third are the overpasses, so overpasses just cross over highways, as the name suggests. So, those are sort of the the three big crossing structures. And we really select which one we use based on what animal we’re focusing on to try to get from point A to point B.
Can you describe the planning that goes into the creation of wildlife crossings?
[0:06:37]
NICKI FREY: Usually, when we’re looking at wildlife crossings, we’re doing that because there already is a problem through the wildlife vehicle collisions, regardless of the size of the animal. And so right away, we have a focus point, we know okay, here’s where the problem is. Now, how do we solve it? And so scientists will be called in to say, to think about the habit of that animal, does that animal migrate? How often does it disperse? What’s its home range size? And so first, we get information about the animal that we’re trying to help. And then we can call in landscape specialists that know about topography, that know about habitat, that know about architecture and how to build these things. And we create a team. And we look at a map of the area and we figure out what’s the most natural place to put this that will help the animal very easily cross. So, we want something that just sort of fits into that animal’s environment, and that animal doesn’t have to learn to cross it, it can just naturally find it and then naturally start to use it. But there’s also logistical constraints. So, it has to be something that the engineers can put into that landscape. So, if there’s already a six lane highway, it’s going to be very difficult to put a culvert underneath of it, we might have to think of another option like an overpass, right. But if it’s something that’s happening in a smaller location, or during new construction, there’s a lot more options for that team to figure out what the best way of going about solving that problem.
What have ecological studies and trail camera data revealed about successfully wildlife crossing designs?
[0:08:19]
NICKI FREY: Through all of these extensive studies, since some of the first overpasses were studied, we know that the design of the structure really can influence what species use it, and how quickly they’ll accept it into their environment. So for example, we know that it’s really important, the length to width ratio of an overpass, so, how long it is versus how wide it is. And some animals, such as elk don’t really like overpasses, we don’t always understand why they don’t like them, but we know that if we have elk, we either need to make a really really wide overpass or we need to focus on making an underpass or a culvert of some sort. So, we can figure out the design—so, whether we want an overpass or an underpass, and then the dimensions, so how wide it is how long it needs to be. If we’re looking at an underpass, scientists know that they really need to be careful about the shape of the underpass. It’s really interesting with prey species like deer and elk, they need to feel comfortable when they look into the tunnel, they need to be comfortable with what they see on the other side. So, it has to be wide enough that when they look through it, they’re understanding that they can get through the culvert, that that opening is wide enough that they look at and say, “Oh, this is big, I can go through this.” We also know that the animals are looking at the habitat on the other side, particularly prey species, they’re looking to see “is the other side safe? Would there be a mountain lion waiting on the other side to eat me?” So, we know from studying these cameras that they are really considering what’s on the other side. So, we need to create habitat that looks comfortable for those prey species and remove any potential hiding places for predators on either side of that crossing.
What advice do you have for reporters covering wildlife crossings?
[Posted April 16, 2024 | Download video]
