The world's largest wildlife crossing

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1:19so we're walking through the over the mulch around the plants around the chaparral There's some sage Two California poppy

1:35I'm Molly Bentley And you're listening to The documentary from the BBC World Service Well I mean I think What you see right now is that there's A handful of colors That pop up here on top of the structure right now There's obvious ones like the California poppy You've got that kind of Beautiful orange-yellow cupped flower and these delicate little stems and little kind of carrot-esque foliage underneath. Now, it may sound like landscape architect Robert Rock is giving me a colorful tour of native California plants. But there's something special about the flowers we're seeing. I think the thing that I'm most surprised by right now is just how well the sage has taken to this site.

2:20It's got this kind of dusty green color and these delicate leaves and obviously the smell of sage is something I think everyone knows quite well. These plants are growing over 10 lanes of freeway traffic on the Wallace Annenberg Wildlife Crossing on the outskirts of Los Angeles, California. When it officially opens in December, it will be the largest wildlife crossing in the world.

2:58Around 300 ,000 to 400 ,000 cars travel the stretch of Highway 101 every day, and that has proven to be a problem for local wildlife, especially the California mountain lion. So the 101 goes in decades ago, cuts off an entire mountain range from the rest of the world. Beth Pratt is the California Executive Director of the National Wildlife Federation, and head of the Wildlife Crossing Fund. The time we put the road in, we didn't know what that did, but science is showing us. It wasn't just the obvious that a mountain lion gets hit by a car. It's that south of the 101, those cats were locked in.

3:38Cats from the north couldn't get in because they get hit, and these cats were inbreeding themselves out of existence. These charismatic cats are iconic in the state with a long evolutionary history. Mountain lions are a holdover. They have an ancient lineage of a couple million years, but mountain lions coexisted with saber-toothed cats here. And when all the megafauna died out, the big stuff, they survived. But it wasn't just mountain lions suffering from genetic isolation. The National Park Service also started studying and doing genetic samples on rintits and western fence lizards. Same thing's happening.

4:18So we know that this fragmentation has vast effects on whole ecosystems. Plants as well start becoming genetically separated. But there may be a solution.

4:33The origin of the very first wildlife crossing structure is a little bit murky. The general consensus is that it was somewhere in France in the 50s. And Europe has absolutely been sort of the place where this technology, this approach has emerged from. Kylie Soans is an urban biologist and road ecologist at the University of Melbourne, who has studied the effectiveness of wildlife crossings around the world. So they were built because people realised that as we fragment the landscape with roads, the animals that they were hunting couldn't move freely across the landscape. So if they wanted to go on a big game hunt, they were also being restricted by roads and couldn't follow animals through the landscape.

5:20So the first wildlife crossing structures were probably largely to facilitate hunting. Can you give us an overview and an overview of the different kinds of wildlife crossings that have been designed? It is so incredible the amount of different designs and the amount of different animals that these structures have been targeted for, right? So we have the overpasses or the underpasses that people might be quite familiar with, but then we also have some that are rope blooders that help monkeys and possums and all of these incredible tree-dwelling creatures get from one side of the road to the other.

5:59Some of the tunnels are very small because they're specifically to attract are salamanders and toads. So it's no thicker than your hand, this very dark, gloomy tunnel that I would never want to travel through, but it's perfect for helping these amphibians cross roads. So there's this enormous range of different designs that target pretty much every species you can ever have thought of. We are trying to help it get a crossroads. While the Wallace-Annenberg Crossing is just one example of the many types of animal crossings in the world, it is also in a class of its own. This is a really exciting project for me because of its size, for starters.

6:42It is a simply enormous structure, but also over an enormous road. And there was a time in road ecology in particular where we were like, there has to be a limit. Can I ask, what seemed to be the limiting factors with the Annenberg Wildlife Crossing? Was it 10 lanes of highway? Is it that simple or is it 10 lanes of highway in Los Angeles? I think it's a combination of the 10 lanes of highway and the landscape that it's in, that were those initial hesitancy points, the points that make people go, no, that's not, that's not going to be possible because we also have this very strong aversion to doing big conservation actions in a human-dominated landscape.

7:28We have for a very long time put urban landscapes in the not important for conservation pile because fine, you'll build this wildlife crossing structure, but it will still be in the city and everything will be bad and nothing will ever use it. That's a really old way of thinking. We know that that's not true anymore. There are so many wonderful conservation solutions that we can apply and urban landscapes are really important places to apply them because that's where people live and can enjoy the nature and that's where nature already lives. We can't keep pretending that nature isn't all around us all the time anymore.

8:09It's making itself very loudly heard. So I think this is a positive story for me on both of those fronts because, you know, not only is it going to be the biggest in the world, but it's being done in a landscape that most of us wouldn't picture when we picture a beautiful, enormous act for wildlife conservation. I secretly find that very exciting.

8:43Beth Pratt says that the scale of the project meant it was met with skepticism from potential backers. I got told I was crazy 10 times a day back then. I had to go to donors, I had to go to elected officials, and I had to say, hey, we've got to connect this landscape or else the mountain lions will die out. I don't know how much it's going to cost. I don't know what it's going to look like, but could you help? So I think there really was a pushback, A, on just the bigness of this, to, for some, wildlife doesn't belong here. And we got pushed back on that. But yeah, we were told, I was told I was crazy.

9:16I'm still told I'm crazy. But we had some early people who were crazy with us. And my heart always, I have a special place in my heart for them because they made it happen. One person Beth didn't have to convince, though, was Robert Rock, the lead architect on the project. I like to think that's why this is a project that I really gravitated towards, is because of the challenge, because of the scale and the number of questions that go along with it, because I appreciate that degree of complexity. And Beth, is it true that he took it in stride the way Robert's telling the story, as though this is a big challenge, he felt that he could do it, he wasn't perturbed?

9:57Is that how it went down? I think that this project has always attracted people who are a little crazy, myself included. I mean, I have to say we have our late nights where, oh my God, how are we going to do this? But what is amazing about this team is here we are really building this impossible dream, visionary project. And you'd think we'd be tearing our hair out every day, but Robert has taken it in stride. I mean, for him, it is a puzzle to be solved, and he does that so well. Now, yeah, there might be a few late nights where I'm not sure he's so low-key about it. That's understandable. The challenges of building a structure like this are extensive.

10:41My name is Ted Hartzig. I'm a senior soil scientist with an engineering firm, Olsen, Inc. Ted and two other scientists worked on the soil for this project, a mycologist and a soil biologist. I remember one detractor said, you just throw dirt on the bridge. No, you don't. You want to restore the soil, not only so that water will drain through it, but so their roots will grow through it, so that oxygen and carbon dioxide will exchange through it. So it literally gives the soil the opportunity to breathe, to drink, to basically be dynamic unto itself. Without the right soil chemistry, water won't flow through it correctly.

11:21Native plants may not take root, and the crossing won't match the adjacent habitat. That means animals may be wary of using the structure. So healthy soil is important. Creating it is a meticulous endeavor. You just don't go build a landscape without understanding the surrounding environment. So I will do a soil assessment. I will collect samples. What is the chemistry of that soil like? What is the physics of that soil like? What is the biology of that soil like? So if we look at a successful ecosystem environment, what type of vegetation is there? If we take samples of the soil that we can have analyzed, evaluated for the microbial content, then we could learn what is the balance?

12:07What are the types of microbes that are in that soil? Oftentimes, it's very similar between areas or regions. Other times, they're very specific ones. and it's really hard to reproduce those. Most of the soil on the crossing deck itself, we had to go look at sources all over the whole northern LA region. What type of soils were being harvested from varying areas that we could get that would mimic the types of soils that are there in the Santa Monica and the Simi Mountains. So we have this conglomeration of soils and this is what we wanted that actually represent that natural environment. That's easier said to find than done.

12:49It took us quite a while to make sure that we had the right soils in place and what we needed. And I really appreciate one of the leaders at the Caltrans Engineering Department who told his contractors, you guys better get this right because we only have one chance to do it right. Boy, no pressure there when someone says you only have one chance. We only have one chance, and so we wanted to make sure we were right. But there's another consideration when adding a heavy load to a suspended structure in Los Angeles. We have a pretty highly seismic area here, and so you don't want to overload the bridge.

13:25And this is where the engineers and we all talk, what can the load-bearing capacity of this bridge be? And so then I went back to, and this is how I determined, what is the bulk density of the soil we could use? How deep can it be? What type of materials can we put into it? How do we calculate almost to a small fraction? What will be the weight of soil we have on this crossing? Another challenge, how to lay heavy soil on a bridge over a busy highway? The answer, carefully. So as we place the soil, we have to do it in lifts and we have to do it carefully so that we keep that porosity or that soil structure consistent and pretty much alive.

14:12So we'll do the first lift. We'll make sure it's even. We'll scarify it to make sure it has a rough surface. We'll do the second lift. We'll do the same thing.

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15:00It's an account co-owned by you and your teen, so you can monitor and engage with the account while your teen learns how to invest and manage money. Learn more at schwab.com. This advertisement feature is paid and presented by GoTurkiye. This is what most people come to Antalya for. Beach, sun, and not much else. And that's fine. But head inland just a little and you can experience a different kind of Antalya. at Köprüle Canyon National Park, one of Türkiye's most accessible places for adventure sports and personal favorite spot of local guide Berfin Özçelik. You can spend your whole day here.

15:38First, you should go to the canyon to do a rough thing. But there is so much more than that. Yes, it's not just adrenaline that's to be found in these hills. High above the river, the pillars of Adam Rock surround the ruins of Selge, an ancient city that's been here far longer than the rafting routes. Selge is like a gem waiting to be discovered. So it's not exactly what you expected from a day in Antalya, but that's exactly the point. Plan your next detour at goturkia.com today. I'm Molly Bentley, and you're listening to the documentary from the BBC World Service. The Wallace-Annenberg Wildlife Crossing is a tricky project.

16:21It needs to hold a lot of soil, and it needs to be quiet. Three to four hundred thousand cars a day make a lot of noise. Acoustical engineers were tasked with the challenge of designing sound-dampening walls on either side of the crossing. The surface texture has a varied character that's been done with an internal form within the concrete pour, kind of giving it a little bit of an undulating texture left to right across the face of the surface and kind of scalloped from the bottom to the top. That variability of the texture gives us this slight amount of refraction to the sound every time a sound wave hits that surface and breaks things up a little bit more.

17:05And I mean, I won't get to the level of geeky detail we did with our acoustical engineer about talking about phononic crystals and how that's like layered into technology like that as well. But we did have those discussions. It got really nerdy. The glare of hundreds of thousands of headlights required adjusting the color of the walls, too. What we were attempting to do with this is instead of using a conventional concrete color that would be really reflective, we integrated a pigment into the concrete to change the color of it to reduce the amount of surface reflectivity of this concrete. So we create a darker, quieter space.

17:44The end result, though, is remarkable. Relatively quiet, the highway below virtually disappears. And with the rugged terrain and an abundance of shrubs and flowering plants, the bridge really feels like a part of the California habitat. For these reasons, says Kylie, the crossing could set a critical precedent. A question we have thought about in road ecology for a very long time is, is there a road that is too big to fix? And people don't want to try something if they're being told that it's probably never going to work. And so I think for a really long time, we have assumed that there was an upper limit to how big a crossing structure could be.

18:31And I think that's been to our detriment. I think we were just a little bit more hesitant than we should have been because there are enormous roads. And this project shows that with the combination of science and engineering and community and government, you really can think of a solution to this problem rather than let it lie in the too hard basket for all eternity. The Wallace-Annenberg Wildlife Crossing has shown that we can build ambitious structures that had long been considered impossible. But now the big questions are, will it work? Will animals use it? Will it repair the fragmented habitat and help save the California mountain lion from extinction?

19:19I visited the structure in June, six months before its official opening. At that point, the platform over the highway was almost complete, but the slopes connecting it to the land on either side were still under construction. Yet animals that could fly or climb had already discovered it. I saw lizards, birds, bees, and even... Oh, oh! Is that a monarch? Again, Beth Pratt. We just saw a monarch on the wildlife crossing. That's the first monarch we've seen up here. that is amazing as we said we've been designing this crossing from everything from mountain lions to monarch butterflies this is a very important overwintering area for monarch butterflies again the 101 is a wall that they cannot navigate across and we just saw the first monarch up here what a moment that is really amazing i hope you have some emotional support when the mountain lion yes i'm gonna need it because that was that was a lot of enthusiasm For a butterfly, yeah.

20:21For that beautiful butterfly. But for animals larger than butterflies, how much do we know about whether wildlife crossings work? Here's Kylie Soans again. We are very lucky that we have an extraordinary amount of studies from around the world on wildlife crossing structures and whether or not animals use them. That's the very first question we have to ask themselves as we've built this remarkable thing. Is it doing what we thought? Do animals see it the way that we hoped? And the answer is yes. So we have conducted a really big review across the world of all these studies. And we found that in 98 % of cases where a wildlife crossing structure had been installed, it had been used by the animals that it was designed for.

21:05And so that's really excellent first pass at the knowledge. That's good news, but it comes with a caveat. The next thing that we have to understand is what does that actually mean for the ability of those wildlife populations to persist in that landscape. Is the fact that they can get from A to B now, is that enough to conserve them in the long term? Are they breeding and intermixing again? Is it improving the genetic health of that population? Is their population size growing now because more of them can cross the road and breed and meet all of those needs that they have? And we don't know that in most cases.

21:47So there is hardly any studies across the world that look at what we call the population level impacts, where we've counted the number of animals and how long they live and how genetically diverse they are. Those studies are really, really rare. And every time they come up, I think I can count the number of studies that have done that on one hand. And that is something we need to get much better at because that's the crux of the problem, right? That's what we want to know is, are we actually saving nature when we put these wildlife crossing structures in? But if we know that the animals are using these crossings, as you said, how could the populations still be in decline?

22:33I mean, there's a few, like one of them is the amount movement might not be enough. So if we know we need 20 different mating occurrences from one side of the road to the other, but the wildlife crossing structure is only allowing five, that could still decline. If we need 50 % of a reduction in roadkill, but the wildlife crossing structure is only providing a 20 % reduction in roadkill, that balance is still out, right? We're still going to see that population decline. But sometimes, and in most cases, we know how many crossing events they are. We don't know if that's one animal who loves to cross the crossing structure a thousand times or a thousand different animals.

23:13And that makes a big difference because if it's just one lunatic animal, if it's just one very excited animal going backwards and forwards and backwards and forwards and backwards and forwards, you can see how that's not necessarily a good thing for the entire population. But if you have a large portion of that local population that is using the crossing structure, that's a much better indicator that you've restored the ecological health for want of a better word. This is going back to how it should be, where all the animals as part of that population can move freely instead of just a couple of animals in that population get very excited about a crossing structure.

23:56After the crossing opens, the National Park Service will be conducting studies to see whether it is helping mitigate the effects of habitat fragmentation at the population level. We're focusing a lot on that camera moment of the first mountain lion crossing, and there's no doubt I am going to be just so emotional over that. Again, you saw how emotional I was over a butterfly. But for me, it's that first genetic test that comes back and shows how the diversity's gone up. And yes, that is very measurable. The Park Service takes blood tests on all the animals they capture. They measure that specifically, and I'm even visualizing the graph they use right now.

24:33When that graph, you know, diversity section goes up, that's really going to be the moment for me where we're like, we did it, it worked. For now, though, Beth hopes the crossing sets an example of what is possible for visionary conservation projects. Crossings come in all shapes and sizes. There's one up in Washington State called the Squirrel, the Nutter Highway. It's literally this little almost like rope bridge for them. So, yes, not everything needs to be a Wallace-Anne-Marie wildlife crossing. Some of these are just really simple solutions. But having said that, we can't shy away from these big ones.

25:13I mean, in some respects, it's these bigger crossings that are solving such monumental blockages to connectivity that we have to get better about accepting. You know, they are hard to do. They're big. They do cost money. But we have to be okay with that because these are the ones that really are going to make such a heavy lift for preserving biodiversity for the wild world. We can't shy away from big.

26:05We'll be right back.