Students from Southern Oregon University collected over a million photos and videos of animals attempting to cross Interstate 5 in Southern Oregon. The students were working with SOU professor Karen Mager to try to understand the best place to put a wildlife crossing to facilitate passage for wildlife in an area well-known for vehicle-animal collisions. The federal government recently announced over $33 million in funding to create an overpass within the Mariposa Preserve of the Cascade-Siskiyou National Monument. It will be the only wildlife crossing over I-5 between Mexico and Canada. Karen Mager joins us to tell us about the project.
The following transcript was transcribed digitally and validated for accuracy, readability and formatting by an OPB volunteer.
Dave Miller: This is Think Out Loud on OPB. I’m Dave Miller. I-5 goes from the Mexican border all the way up to the Canadian border – 1,381 miles. There’s currently no wildlife overcrossing for that entire stretch. A crossing is a dedicated landscaped path that lets animals safely cross from one side of a highway to another. For years now, a group of researchers, scientists, engineers and advocates have been partnering on a project to create the first such crossing over I-5. With the recent announcement of a $33 million federal grant, it seems like the crossing is going to become a reality. It’ll be south of Ashland in the Cascade-Siskiyou National Monument.
Karen Mager is an associate professor of environmental science, policy and sustainability at Southern Oregon University. She joins us now. It’s great to have you on Think Out Loud.
Karen Mager: Thank you so much.
Miller: What makes that particular part of the world special, in terms of wildlife and habitat?
Mager: Southern Oregon is a huge biodiversity hotspot. And the reason for that kind of makes sense if you look at an elevation map of the whole western seaboard. We have coast mountain ranges, running the length of the United States and we have our interior ranges, like the Cascades and the Sierras. But if you look at Southern Oregon, it’s one of the only places where we have an east-west mountain range – the Klamath-Siskiyou region – that really connects the coast to the interior. So it’s a huge hotspot of biodiversity, and a really important location for genetic exchange and movement of wildlife, especially when we’re thinking about a changing environment in the future with climate change.
Miller: One of the things you’ve done with your students for a number of years now is wildlife monitoring there. What have you done and what have you learned?
Mager: Yeah, we’ve been having a lot of fun out there. We have collaborated with Charlie Schelz, a retired ecologist from the Cascade-Siskiyou National Monument and, at this point, 14 different undergraduate research assistants to study how wildlife use the interstate corridor with camera traps. So your listeners might have heard of camera traps before. There are game cameras that hunters use. And when we deploy a large set of them, more than 30 in our case, we can see patterns in how wildlife are using this highway corridor.
One of the key things we’ve learned is that we see the full representative of medium to large mammal species in this area. But we see even greater diversity, especially of some of our large predators and rare species like the Pacific fisher, on the south slope of the Siskiyou summit, closer to the California border. That information really helped us to select this particular site as a good one for a wildlife crossing.
Miller: How common are wildlife collisions around that stretch of I-5?
Mager: Good question. So ODOT monitors wildlife collisions and our area is one of those red zones, with a really high frequency of wildlife collisions. And even though we know that there’s a high frequency of wildlife collisions, we also know that those are unreported. A lot of wildlife are hit, then wander off the road and are never documented.
One of the most compelling moments that really inspired my partners and I to do this work was a few years ago. As we were driving along I-5, looking at potential sites to study, we came across a freshly killed bear right on the side of the road. That was a really compelling moment for us to see that bear and say, “OK, we have to do this work.”
Miller: You mentioned medium to large mammals, predators, Pacific fisher, you mentioned a bear. Can you give us a sense for the range of animals that live in this area?
Mager: Absolutely. What’s probably a surprise to no one, deer are our most abundant medium to large animal. It’s been really important to document how they’re using the area because we know deer are the most likely to be involved in a wildlife vehicle collision. People are afraid of hitting deer. It can be really dangerous. We do also have elk in the area, which can also be a really costly animal to hit in a wildlife vehicle collision. We have mountain lions, coyotes, bears, bobcats, Pacific fishers. We’re at the northern edge of the ringtail, which is this really cool kind of raccoon relative. So we have a lot of diversity here.
What’s exciting is that we’ve documented these different animals using the habitat in different ways. But there’s so much habitat diversity within just a couple miles of this wildlife crossing that we think we’re going to be able to attract and serve that whole diversity of animals.
Miller: Can you describe what this wildlife crossing will look like?
Mager: Yes, so this is going to be an overpass. It’s gonna go over the highway. There will be two arches that actually sit on top of the highway lanes, and then above them will just be essentially an enormous wide bridge that’s constructed to feel comfortable to wildlife. So that will include walls that help to dampen sound and block out lights, which we know can really influence the feelings of safety that wildlife have in crossing the road. There will be a very deep layer of soil, and the bridge will be planted with a full complement of native plant species to create a habitat that’s comfortable for wildlife to cross, that provides cover for smaller wildlife that need that.
And then the bridge itself is actually going to be connected to a couple miles of fencing to the north and to the south that help funnel animals towards the wildlife crossing. And this fencing is really cool. It’s got these jump outs on it, so that if an animal accidentally ends up in the freeway, they can easily jump out to the safe side of the fence. But animals on the safe side of the fence won’t be able to easily get into the highway.
Miller: So the idea of the fence is to prevent animals from trying to cross in unsafe places. In other places, is that enough to get wild animals to actually go where scientists want them to go? I guess I’m just wondering how you get a ringtail, or a fisher, or a bear, or a coyote to use this human infrastructure?
Mager: I have a two-part answer to that question. The first part is that Oregon is actually one of the places where we’ve got really clear evidence that a wildlife underpass under the highway can have that impact. Some underpasses have been constructed below Highway 97, kind of near Bend. And they’ve seen a 90% reduction in wildlife vehicle collisions with elk and deer in that location. And researchers have documented a whole lot of wildlife traveling along those fences, jumping out through the jumpouts to safety and finding that wildlife underpass. So we have evidence that this is succeeding in Oregon.
Overpasses that have been constructed elsewhere in the world have shown to be incredibly effective for a wide variety of mammal species, especially some of those bigger deer and elk. But honestly, this is still a new area of study, and the funding source that funds this wildlife overpass is referred to as the Wildlife Crossings Pilot Program. They’re acknowledging that we’re still trying to pilot these approaches to improving wildlife passage, study them and understand them better. And one of the things that’s most exciting to me, to my colleagues and students here at SOU is that we have some rare pre-construction data that will enable us to really evaluate how we’re improving wildlife passage, once this is built.
Miller: For me, personally, if I were given the choice between walking through a tunnel underneath an interstate highway that would go on for, I don’t know, half a mile, or being on a grassy arch in the open air above it, I would definitely take the open air. Is there any science to suggest what animals prefer: a tunnel or an overpass?
Mager: Yeah, there is. We know, for example, that many ungulates like deer and elk prefer a more open passageway and overpass. Even though those aren’t our most rare species, they’re most likely to be involved in collisions with vehicles. It’s really helpful to have an overpass for them. But interestingly, some studies have found even species that are comfortable with an underpass will sometimes switch to an overpass.
So, for example, one of the really fun parts of our research is that we’ve documented whole bobcat families using existing culverts to go under I-5. They’re some of the only species that will use those culverts because, as you say, it’s kind of a dangerous, damp, dark, scary place for most animals. But I’ve read research that has suggested that once an overpass is constructed, bobcats will actually switch to using the overpass instead. So there’s a lot of evidence to suggest this will benefit many species, especially with vegetation that allows those animals that do like a bit of cover and concealment to feel more comfortable there.
Miller: This seems like an amazing place to visit when it’s all said and done. But I also imagine having a bunch of people there, or leaving trash, or just hanging around is going to make wildlife a lot less likely to want to use it. Are people going to be prohibited from being there?
Mager: I actually don’t know the answer to that yet. I know this is on public land. It’s an area that people visit occasionally right now. Certainly, I go there with my students. And it’s an area of active conservation and restoration projects within the Cascade-Siskiyou National Monument in general. So it’s too early to know what the policies will be, but anybody who’s driving on I-5 is definitely going to get to see this as they’re driving. The overpass will be kind of an amazing, beautiful “welcome to Oregon” statement as you drive in from California. And it’s going to have artwork on it. So my hope is that a lot of people will be able to experience it that way.
Miller: What is the timeline for this project right now?
Mager: Of course, these things can change, but based on recent conversations with the Oregon Department of Transportation, who’s managing this project, we’re expecting early 2028. So one of the great things is that the engineering design for this project is already completed and the full complement of funding has been secured. So, of course, there’s going to be bidding, compliance, things like that. I can’t speak to specifics, but we expect that in early 2028, construction will start. And depending on the timing, the hope is that it’ll just be a single construction season.
Miller: You mentioned there’s going to be sound dampening, but I don’t imagine that’s going to completely block out the noise or drone of 18-wheelers passing underneath. Do wildlife just get used to it?
Mager: Yes and no. There’s some really interesting research. This isn’t specific to this area at all, but in many areas where people have studied wildlife habituation to human presence, they found that wildlife do seem to habituate behaviorally to being around human presence. But they still experience a pretty high level of stress even when they’re habituated. So this wildlife overpass is amazing, but it’s not going to fix the bigger problem that wildlife are living alongside our noisy infrastructure.
Of course, wildlife might still be hesitant about crossing the highway in general, but we know that wildlife have compelling reasons to do it – whether it’s to find mates, to find food, to find water, disperse to new territories. Wildlife are already trying to cross the highway, and it’s leading to some really tragic consequences. So this will provide them a much better way to do that when they do decide to make that leap.
Miller: Karen, thanks very much.
Mager: Thank you.
Miller: Karen Mager is an associate professor of environmental science, policy and sustainability at Southern Oregon University.
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