'Crossings' author Ben Goldfarb says cars and roads are reshaping our ecology Environmental journalist Ben Goldfarb says cars are killing animals, while highways cut off them off from their food sources and migration paths. His new book is Crossings.

Cars are a major predator for wildlife. How is nature adapting to our roads?

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This is FRESH AIR. I'm Terry Gross. Roadkill - you've probably seen your share of it and maybe even accidentally killed an animal on the road. Cars are weapons of death for wildlife, large and small, that live in wooded areas near the road, from salamanders to birds, skunks, possum, deer, mountain lions and bears. The roads themselves are problems, too, cutting off animals from their sources of food, migration paths, animals to mate with, even messing with evolution. The dire threats roads have created for animals and ways to eliminate or at least moderate those threats, well, put it all together and you've got what's called road ecology.

The world of road ecology is filled with fascinating insights into animal behavior, the threats they face from roads and solutions that have been tried. I just learned about this in the new book, "Crossings: How Road Ecology Is Shaping The Future Of Our Planet." My guest is the author, Ben Goldfarb. His previous book, titled "Eger: The Surprising Secret Life Of Beavers And Why They Matter," won the PEN/E.O. Wilson Literary Science Writing Award. Goldfarb has been published in The Atlantic, National Geographic and The New York Times. He lives in Colorado. Ben Goldfarb, welcome to FRESH AIR. I want to say, am I the only person who didn't know what road ecology was?

BEN GOLDFARB: No, you're certainly not. You're in the vast majority in not knowing what road ecology is.

GROSS: Good. So let's talk about it. I want to start with what you say, that roads signify freedom in Kerouac novels like "On The Road" and in Springsteen songs, but they're death traps for animals. Describe how roadkill is affecting survival of certain species.

GOLDFARB: You know, I think that the animals that we tend to see by the side of the road are those really common critters like whitetail deer and raccoons and gray squirrels. And as a result, I think that we sometimes fail to recognize that roadkill is a true crisis for biodiversity. You know, it's one of the major contributors to our current mass extinction event. And for species like ocelots and Florida panthers and tiger salamanders, roadkill is a true existential threat. It's one of the significant checks on animal populations and the diversity of life on this planet.

GROSS: You say that wild ecosystems weed out the sick and the old, but roadkill is an equal opportunity predator as likely to eliminate the strong as the frail. So what's the significance of that, even for evolution?

GOLDFARB: Right. So, you know, you could imagine that in a natural ecosystem, you know, the predators - the wolves or the cougars - are targeting those older, sicker animals, those older, sicker deer or elk or the young fawn, you know, who's struggling to survive. So, you know, natural selection has this way of, again, targeting the least fit members of a population. But roads are indiscriminate. You know, cars take out the old, the young, the middle-aged, the strong, the weak, without any discernment. You know, a car or a truck doesn't care whether you're a diseased, older animal or one in the prime of your life. And as a result, you know, roadkill is weeding out - roadkill is not only eliminating animals. It's, in many cases, eliminating those healthy animals that populations need to remain strong. So in that sense, it's an equal opportunity and indiscriminate predator.

GROSS: Have you ever accidentally killed an animal on the road?

GOLDFARB: Terry, I'm ashamed to admit that I've accidentally killed many animals on the road. I killed a marmot here in Spokane, where I'm currently speaking to you from a couple of years ago. I killed an owl a few weeks ago. It's a terrible feeling. After I killed that owl driving through Southern Colorado, I had to pull over and take a few minutes to compose myself because I was miserable about it.

GROSS: Do you have an electric vehicle, I guess, or a hybrid? I'm just wondering, you know, like, they're so much quieter than cars. Maybe animals and birds don't hear them coming in the way that they'd hear a regular car.

GOLDFARB: Yeah. That's - it's an interesting question and certainly something that's been hypothesized - right? - that electric vehicles compared to a conventional internal combustion engine vehicle are basically silent. But the thing about road noise and road noise pollution, which is a huge problem, is that at highway speeds, especially, which are the speeds at which you're most likely to hit an animal, most of the noise from a vehicle actually comes from the tires. You know, what you're hearing when you hear that kind of monotonous hiss of the interstate is actually - that's the sound of the tires gliding along the asphalt and the little air pockets that are trapped in the treads of the tires popping. That's the - that kind of pattern noise that you hear from big highways. So at those faster highway speeds, cars are still pretty audible, thanks to the tires rather than the engines.

GROSS: Now, you've mentioned some of the losers - some of the animals that are losers because of roadkill and because of roads. Some of the winners are vultures and other birds of prey that feast on dead animals like roadkill. Are they starting to overpopulate as a result?

GOLDFARB: They're certainly increasing in population and following these linear trails of carrion that we've created, you know, into new habitats. I don't think they're overpopulating. You know, one important thing to keep in mind, of course, is just how much wildlife used to exist on this continent prior to the mass extinction events during the Pleistocene, you know, we had these giant ground sloths and enormous beavers and mammoths and mastodons. You know, the whole continent was carpeted in meat for scavengers. And there actually - there were - there used to be massive vultures called teratorns that feasted on all of this carrion that was killed by animals like short-faced bears and dire wolves and saber-toothed cats.

So in some ways, you know, the land being carpeted with carrion for large, scavenging birds is sort of the normal state of affairs in North America. You know, the car is creating this necrobiome, you know, this ecosystem that revolves around dead animals. And that's not to excuse roadkill or to justify it as a natural process. It certainly isn't. But, you know, I think it does speak to the fact that roads create ecosystems in their own right. And there are animals that benefit from them in some ways.

GROSS: You know, evolutionary protections don't necessarily help on the road. Like, skunks, like, their odor scares, you know, it turns off other animals and therefore, theoretically stay away. But...


GROSS: ...You know, a horrible odor isn't going to defeat oncoming traffic.

GOLDFARB: Right. Right. And that's, you know, certainly true of so many species, right? A porcupine's quills are not going to defeat oncoming traffic. A turtle's shell is not going to defeat oncoming traffic. And I think that's one of the really cruel things about roadkill, in some ways, is that it hijacks evolutionary history and renders all of these ancient defense mechanisms maladaptive. You know, all of those strategies - a skunk's spray or a porcupine's quills or a turtle's shell - those worked for thousands of generations against coyotes and foxes and hawks and other more natural predators. But, you know, against an F-250 barreling down I-90, they're not only useless, they're actually maladaptive. Standing your ground and hunkering down is the worst possible thing you can do.

GROSS: Some species evolve to deal with roads. And I'm thinking of the cliff swallows - a bird I was never familiar with until reading your book. But you write, if you've ever driven across the U.S., you've passed beneath the wings of this small, plucky songbird. So they've been winners and losers. First they were losers 'cause they were dying out because of the roads. But then they became winners and learned to, like, thrive on roadsides. How do they manage to thrive on roadsides?

GOLDFARB: Yeah. So cliff swallows are - they're birds that - they build these little, mud nests. And, you know, historically, they built them on the sides of cliffs. That's how they get their name, of course. But, you know, we've created all of these good nesting habitats for cliff swallows in the form of our bridges and highway overpasses. And, you know, they plaster these little mud nests to that concrete substrate that we've provided them. But, of course, you know, nesting on a highway overpass is very dangerous. And, you know, they become roadkill like so many other species.

And, you know, this research into cliff swallows was conducted by a scientist named Charles Brown starting in the 1980s. And, you know, he observed in Nebraska that cliff swallows were becoming roadkill. But over time, what he saw was that they became roadkill less and less often. They were hit with increasing rarity over time. And what he figured out from examining specimens over many decades is that they were actually evolving to get shorter wings. Their wings were growing shorter. And, you know, you can imagine that if you're a bird, having a long wing is good for straight flights, whereas having a shorter wing is good for tight rolls and turns and pirouettes, the kind of quick movement that you'd use to maneuver out of the way of a barreling 18-wheeler.

So over time, those long-winged cliff swallows were more susceptible to roadkill and were weeded out of the population. And the cliff swallows evolved to have shorter wings and to be more nimble to avoid oncoming traffic. And, you know, I think that we think about evolution as being this process that transpires over the course of many centuries or millennia or even millions of years. And yet in Nebraska with cliff swallows, it happened in the geologic blink of an eye, just a few decades, which I think is an amazing testament to how transformative and powerful roads are as this selective force that's changing the lives of wildlife all over the world.

GROSS: One biologist told you that once the environment is ruined, all we'll have left is rats, cockroaches and cliff swallows. Are they nice birds (laughter)? Will we be happy to have them?

GOLDFARB: I'm certainly happy to have them. You know, they're beautiful birds. And, you know, I just have such admiration for them that they've been able to carve out this niche within our infrastructure. And, you know, there are so many great examples of that. Cliff swallows are evolving, and other animals are changing their behavior to adapt to all of the infrastructure we've created. You know, Chicago's coyotes, a very famous urban wildlife population - you know, they allegedly look both ways before crossing the street and use crosswalks at red lights. You know, there are crows in Japan that have learned to drop their nuts on the road so that cars actually crack the nuts for them. And then they'll scurry out at the red light and pick up...

GROSS: That's wild (laughter).

GOLDFARB: ...The nut that the car cracked open. Right. So, you know, we think about roads as these forces that are universally or exclusively harmful to animals. And certainly, they're incredibly destructive. But, you know, wildlife is also incredibly adaptive and clever. And they're finding ways to make a living in our midst.

GROSS: So tell us a little bit more about the typical problems besides roadkill faced by animals from roads and cars.

GOLDFARB: Yeah, you know, there are so many different road- and traffic-related ecological problems that it's hard to know where to begin. I think that one of the most pernicious ones is the barrier effect, right? The steady stream of traffic that rolls down so many busy highways forms what some biologists have called the moving fence, you know, this impenetrable wall of vehicles that animals don't even attempt to cross. And I think that's a difficult problem to solve because, again, we've all seen the - you know, the dead deer or opossum or squirrel by the side of the road. But, you know, what you don't see are the animals that never even attempt to cross. And those animals can really suffer as a result. And in some ways, that barrier effect can be worse than roadkill itself.

You know, in the book, I write about mule deer, these deer that migrate across large distances in the American West. And, you know, in some cases, they've had vast swaths of their habitat lopped off by this moving fence of traffic on big interstates like I-80. And they can't access their winter range, you know, these low-elevation valleys that they need to survive at the end of their migration. And, you know, in some years, 40% of these mule deer herds have starved. And, you know, that's, again, worse than roadkill in some ways. You know, these animal populations can survive a handful of collisions in many cases. What they can't survive is losing all of that habitat and suffering starvation as a result.

GROSS: Well, let's take a short break here, and then we'll talk some more. If you're just joining us, my guest is Ben Goldfarb. His new book is called "Crossings: How Road Ecology is Shaping The Future Of Our Planet." We'll be right back. This is FRESH AIR.


GROSS: This is FRESH AIR. Let's get back to my interview with Ben Goldfarb, author of the new book "Crossings: How Road Ecology Is Shaping The Future Of Our Planet." It's about all the dangers that roads and traffic create for wildlife, from roadkill to disrupting migration patterns, cutting off access to food and even messing with evolution. The book is also about ways to protect wildlife from cars and roads.

Part of road ecology is creating roadsides that have plants and weeds that would be nourishing for the wildlife that lives by the roadside. Can you tell us a little bit about how that's being done? And what are some of the plants that are helping to nourish wildlife?

GOLDFARB: So the kind of the archetypal case study for this idea of roadsides as habitat is really the monarch butterfly. And, you know, monarch butterflies migrate across vast distances. And in the Midwest, their migration just happens to almost perfectly coincide with I-35, which runs from Minnesota to Texas. And, you know, in the middle of the country, so much of the landscape has been converted to monoculture, to corn and soy. And those monarch butterflies have lost so much of the milkweed that they need to survive. Their caterpillars feed exclusively on milkweed. And, you know, those roadside strips are some of the last remnants of milkweed, the last native prairie left in the Midwest, and have become a monarch habitat as a result. And, you know, a bunch of state departments of transportation have branded that I-35 corridor the Monarch Highway, you know, because it's sort of the source of milkweed running through the middle of the country. But, of course, you know, living by the road is a dangerous place to be, and millions of monarch butterflies are killed by cars.

You know, we don't really think about insects as being roadkill, right? But, you know, certainly monarch butterflies and so many other pollinators become roadkill themselves. And so it's sort of incumbent, I think, on the agencies who are governing or managing these roads to think about that, too, you know, to make sure that they're producing more butterflies than they're potentially killing by luring these animals to the side of the highway. That's obviously - it's a potentially valuable source of habitat for these insects. But, you know, it's also not the ideal place to live if you're any critter.

GROSS: Well, I would think even, like, the wind pattern caused by cars whizzing by would disrupt the flight patterns of monarch butterflies.

GOLDFARB: Yeah, there are scientists who have observed monarch butterflies being torn apart by those wind vortices off of the back of passing trucks. So you know, it's not just the traffic itself, you know, it's also the road salt which is potentially an issue. You know, all of the road salt that we apply as a de-icer, you know, 20 million tons every year in the United States, is running off roads and potentially changing the chemistry of vegetation along roadsides. And then there's the cadmium and the zinc and the copper from our cars. And there's the tire particles and the microplastics, right? So you know, the road is a very chemically complex and potentially challenging environment for monarch butterflies and everything else.

GROSS: A lot of roadsides have, like, grass and flowers. They look kind of like lawns, very pretty.


GROSS: But you say that's often, like, really bad for the wildlife living there. What's wrong with that?

GOLDFARB: The lawn effect, you know, is problematic in that, you know, those roadsides are - again, they are potentially habitat, right? You know, you could imagine - and many states have done this - you know, planting roadsides and pollinator-friendly flowers and shrubs that provide fruit for birds and so on. You know, those roadsides are, again, valuable habitat if they're managed properly. You know, again, the risk is just luring animals into what scientists know as these ecological traps, you know, these situations in which you promise resources like nectar-producing flowers or fruiting shrubs, and then, you know, you're drawing animals into this dangerous situation.

GROSS: You know, you mentioned that a lot of highway noise is really, like, the wheels going at high speed, the tires going at high speed. That's what you're hearing is the tire friction. Are most animals scared of the highway noise? Is it a warning to them?

GOLDFARB: Yeah, animals definitely avoid noisy environments. And, you know, I think we don't recognize this, but, you know, road noise is a form of habitat loss. You know, that's chasing animals away from these vast areas. There's a really wonderful experiment done by researchers at Boise State University about a decade ago. And what they did was basically record the noise of traffic and then play it through speakers in an unroaded (ph) area.

So they created what they called a phantom road, this just road of noise that had no physical road associated with it. And what they found was that, you know, many species of songbird avoided that area, and the ones who did stick around were in worse body condition. So you know, you could imagine that if you're a little songbird, you know, you have to spend all of your time listening for predators, you know, the flap of a hawk's wings or a fox creeping through the brush. And if the noise of a road masks those auditory signals, you have to look for predators instead. And every minute that you're looking around is a minute that you're not feeding on berries or insects or whatever you eat.

So the birds in this area were less fit to complete their migration because they were looking around for predators all the time rather than listening for them because all of that traffic noise masked their hearing, essentially. So you know, there are lots of studies showing that animals avoid noisy areas, and roads are a huge contributor to this noise pollution problem.

GROSS: And animals can't communicate with each other easily if the noise from traffic is obscuring the animals' sounds.

GOLDFARB: Yeah, exactly. You know, there was a really wonderful study that was done during the spring of 2020 during the COVID lockdown, which was really ultimately one of the biggest inadvertent experiments in the history of road ecology. You know, what happens when you stop the vast majority of traffic for a couple of months? And what these researchers in the Bay Area found was that white-crowned sparrows, you know, these wonderful little songbirds, as soon as that traffic noise went away, they started singing songs that went into much wider ranges and were more complex and intricate. They basically became better singers because they didn't have to scream over the noise of traffic all the time, which is just an incredible testament to both how road noise is changing these animals' lives and also how flexible and adaptable these animals are. They're just waiting for traffic to go away so that they can resume their natural lives.

GROSS: Well, let's take another short break here and then we'll talk some more. If you're just joining us, my guest is Ben Goldfarb. His new book is called "Crossings: How Road Ecology Is Shaping The Future Of Our Planet." We'll be right back after a short break. I'm Terry Gross, and this is FRESH AIR.


GROSS: This is FRESH AIR. I'm Terry Gross. Let's get back to my interview with Ben Goldfarb, author of the new book "Crossings: How Road Ecology Is Shaping The Future Of Our Planet." It's about all the dangers that roads and traffic create for wildlife - from roadkill to disrupting migration patterns, cutting off access to food and even messing with evolution. The book is also about ways to protect wildlife from cars and roads. Goldfarb's previous book, titled "Eager: The Surprising Secret Life Of Beavers And Why They Matter," won the PEN/E.O. Wilson Literary Science Writing Award. He's been published in The Atlantic, National Geographic and The New York Times.

Let's talk about a specific example of a highway that has created problems for animals. And I'm thinking of one of the freeways in California - the Ventura Freeway, US-101. And it split Santa Monica into two separate parts. What's the difference between those two parts, and why is that significant?

GOLDFARB: Yeah. I'm glad you brought up that freeway because it's such a clear example of the harms that roads, and especially these really high-traffic roads can create. So what happened in the Santa Monica mountains, essentially, is that when that freeway went through, it cleaved the mountain range in half, and it isolated so much of the wildlife south of the freeway, especially mountain lions. See; there's this little population of mountain lions that lives west of Los Angeles, a very urban area, of course. You know, these animals are living very close to the largest city in the country, kind of amazingly. But, you know, they've been totally cut off from other mountain lions by this freeway. They're essentially in this little island of habitat, and that's been disastrous for them.

First, you know, the young, male mountain lions can't disperse. They're trying to find their own territories, get away from the bigger, older, more established males. But they sort of bounce off of these high-traffic freeways like Ping-Pong balls. They can't get out of this island because of all of the traffic. And they end up in conflicts with, in some cases, their own fathers and get killed by their - you know, their own fathers. And even worse is that new mountain lions can't enter the population, right? No new animals can come in because of these steady walls of traffic on the 101 and the 405 and these other major freeways. And as a result, the mountain lions trapped on this - in this little island have had to resort to mating with their own relatives and in some cases, male mountain lions have bred with their own daughters and granddaughters and great-granddaughters, and the population has become chronically inbred and has begun to suffer genetic defects as a result.

GROSS: Like what?

GOLDFARB: Well, the most - one of the mountain lions that was captured in the last couple of years had a kinked tail and an undescended testicle. And that doesn't sound too catastrophic, but those are early signs of inbreeding. And in other populations of mountain lion, like the Florida panther, those sorts of symptoms have been really precursors to much more serious problems, like heart defects. So this population, this is - these are sort of these ominous warning signs that this population is in trouble. And scientists have written that they've entered this extinction vortex, this long-term doom spiral. And if nothing is done, they're going to die out.

GROSS: Yeah. And you were talking about how the freeway has divided Santa Monica into two and that, you know, the mountain lions can't cross the highway. And the average home range for female mountain lions is 134 square kilometers. That's a really big distance. But now they don't have that much to roam because of the highways dividing the region.

GOLDFARB: Yeah. That's exactly right. You know, these are large animals that patrol huge territories and have to range widely in search of prey. And when these big freeways, you know, these - I mean, these freeways are some of the most densely trafficked roads on Earth. You know, the 101 has literally hundreds of thousands of cars every day. And there's just no way for a mountain lion to reliably cross such a busy freeway, even at night. And as a result, the population is completely divided and cut off from genetic reinforcements that might save it.

GROSS: So one solution that was tried to mitigate the problem of the freeway splitting Santa Monica in two was a bridge for the large cats - for mountain lions, I guess for bobcats, too.

GOLDFARB: Yeah. So there's a giant wildlife crossing that's under construction right now - this enormous overpass or a bridge that is - it will be completed by 2025. It's going to cost $90 million altogether, and it's going to allow interchange between those isolated Santa Monica mountain lions and mountain lions elsewhere in California. So, you know, the idea is that by bridging the 101, this highway that's dividing these populations, you know, mountain lions from the Santa Monicas can leave that population and find their own territories. And maybe even more important, new mountain lions can come in and refresh that gene pool.

GROSS: So what is this wildlife bridge going to look like? 'Cause I'm trying to figure out how do you make a bridge for mountain lions and prevent people from hanging out on the bridge.

GOLDFARB: Even calling it a bridge is, in some ways, a misnomer. It's really this gigantic, new piece of prairie and woodland and chaparral that's going to be created from Earth. It's this sort of giant span that's going to cross the highway. And they're also building up the habitat on either side of it. It's going to have native plants and shrubs and trees atop it. And that's really important because, you know, mountain lions are sort of the flagship species for this ecosystem, but there are also all kinds of other critters that are affected by this freeway. There are bobcats and coyotes and deer and even small birds are, in some cases, reluctant to fly over the freeway and will benefit from being able to hop from shrub to shrub. And there are lizards and snakes and insects. And so they're trying to account for all of these different species by building different habitat features and just trying to account for the whole community of organisms.

GROSS: Another thing that's being done to protect animals from the obstruction of roads and other dangers posed by roads and cars is underpasses. What kinds of creatures are those underpasses being used for?

GOLDFARB: Those underpasses are - they're used by all kinds of animals. You know, really, they originated as passages primarily for deer especially in the American West. You know, in the East, whitetail deer are the deer species that's everywhere. And, you know, whitetail deer - as anybody who's ever driven around a suburb can attest - are basically everywhere, right? They're just all over the landscape. Whereas in the West, there are mule deer, kind of a sister species to whitetail deer, and mule deer are, in many cases, migratory. And the reason for that is that the West just has a much harsher climate - you know, places like Wyoming, you know, that are sunbaked half the year and snow-covered the other half. And deer have to migrate across large landscapes to find food and water and shelter and all of the things that they need. And so they form these big migratory herds - not only deer but also elk and antelope and all of these other species that are out there, these ungulate species, hoofed animals. And as a result, you know, sometimes, these big herds of mule deer will migrate across a highway on the way to the place they're trying to get.

And when that happens, you know, it can be disastrous. Many, of course, get hit by cars. And in some cases, the highway prevents them from migrating altogether. So, you know, in those cases, really starting in the 1970s, engineers began to build these big underpasses that allowed these migrating herds of mule deer to cross beneath the road successfully. And, you know, now all kinds of creatures, from mountain lions to bobcats to coyotes to otters, have used these underpasses, which are, you know, being built rapidly all over the country. And, you know, they're certainly one effective way of getting animals across a highway.

GROSS: I just have this image of, like, turnstiles at the beginning...


GROSS: ...Of the underpasses. I'm from the city. So, again, like, similar to, like, the overpasses, how do the animals know that this is an underpass for their safety, and it will help them get to the other side?

GOLDFARB: Right. So a couple of ways. The first thing, again, are those fences that go along the road. So the animals are trying to migrate across the road. They hit a fence. They, you know, turn left or right, and they start walking that fence line, looking for a safe way across. And then they reach that underpass and say, OK maybe this is how we can keep going across the highway. And then the really wonderful thing that happens over time is that they learn to use these structures. You know, there are many wonderful case studies of mother deer that teach their fawns or grizzly bears who teach their cubs. And passage rates, you know, the number of animals who feel comfortable moving through these structures actually increases over time as the whole population acclimates to these passages.

And as that happens, you know, more and more animals walk through. And that creates little animal trails, little paths, game trails that subsequent generations can essentially follow to the crossing. You know, in some places, you see these amazing networks of game trails, spider webbing the area around a wildlife crossing, just so many generations of hooves and paws all walking through the same place, which is very cool. You know, one road ecologist told me that it's almost like the land itself learns how to use these structures together.

GROSS: When you're driving on a country road and you see a sign saying deer crossing, what do you do?

GOLDFARB: I mean, I think that the answer for most people is nothing. You know, there are so many deer crossing signs out there that they're essentially white noise. You know, I heard one biologist refer to them as litter on sticks, which I think...

GROSS: (Laughter).

GOLDFARB: ...Gets at them nicely, right? They're just everywhere. You know, I've seen signs that say things like deer crossing next 40 miles. You know, so...

GROSS: Yeah.

GOLDFARB: ...Are you supposed to be vigilant for 40 miles? No, of course not. So, you know, I don't think that - there's plenty of research showing that signs are not an effective way of dealing with this problem. And I think it's the default Band-Aid that we tend to slap on this issue, but they don't really do a whole lot.

GROSS: Let's take another break here, and then we'll talk some more. If you're just joining us, my guest is Ben Goldfarb, author of the new book "Crossings: How Road Ecology Is Shaping The Future Of Our Planet." We'll be right back. This is FRESH AIR.


GROSS: This is FRESH AIR. Let's get back to my interview with Ben Goldfarb, author of the new book "Crossings: How Road Ecology Is Shaping The Future Of Our Planet."

Let's talk about national parks. They're supposed to be safe spaces for wildlife, and they're also supposed to be places where people can come and experience natural beauty and hike and camp out and learn to really respect and cherish the wild. But those are kind of contradictory missions, bringing people in and protecting wildlife. And continuing that thought, there's something called windshield tourism in national parks. Explain what that is.

GOLDFARB: Yeah. You know, in some ways, national parks are what one historian described as windshield wildernesses, you know, these places that are really designed to be experienced from your cars. And, you know, that's, again, I think, one of the ironies of roads. You know, I've had so many wonderful wildlife encounters while driving. You know, I've seen grizzly bears and wolves and bobcats and all kinds of fantastic creatures in my car. And yet, of course, the presence of my car is negatively affecting their lives in so many ways. So that tension, I think, between roads and cars allowing us to experience nature and helping us love it, even while roads and cars are destroying the thing that they're helping us to love, is a tension that I find fascinating and try to explore in the book.

GROSS: One way of cutting back the number of cars in the national parks has been buses, so a lot of people are in one vehicle instead of car after car after car. Another approach has been limiting the number of cars per hour allowed on any given road. How are those things working out?

GOLDFARB: One of the places that I went working on this book was was Denali National Park, where there's a wonderful shuttle system. And, you know, one of the cool things that they they do in Denali is not only do they compel visitors to ride these buses rather than taking their own private vehicles, but they, at least in theory, manage the buses in such a way that there's space between them for wildlife. So if you're - you know, if you're a dall sheep, a very iconic animal in Denali National Park, you know, trying to migrate across the road, you know, the buses are moving at intervals that theoretically permit animals to cross between them. So they're - ideally, there's - you know, there are these gaps between the buses that give creatures a chance to migrate.

And, you know, I think that that's a strategy. It seems like it's working reasonably well. But, you know, of course, there's also pressure from the tourism industry and from visitors themselves. You know, we want transit systems that deliver a frequent and reliable and fast-moving form of transportation, not one that has gaps baked into it for wild animals. So you know, I think, ultimately that system is working. But, you know, it is controversial in some quarters, I think.

GROSS: One of the problems that animals and people are facing is climate change. A lot of animals, birds have to change the regions they're in because they're designed for warm weather or cold weather or dry weather, and the climate is just changing. And they can't survive in that climate the way they used to, so they have to move. And, you know, in terms of long-term stuff, cars are part of the cause of climate change because of all of the, you know, carbon that's released from cars. So can you talk a little bit about climate change and the kind of wildlife that you write about?

GOLDFARB: Certainly, yeah. As you say, one of the things that's going to happen with climate change and is already happening is that species are changing where they live. You know, often they're moving north or upslope into cooler climates. You know, and that makes it even more important that we give them opportunities to cross highways, right? They're trying to find new habitats and roads are preventing them from doing that. You know, one of the really cool ideas that's out there in the ether now is building new types of wildlife crossings, wildlife overpasses that are made out of different materials that are lighter and can actually be disassembled and reassembled.

So, you know, you could theoretically put up a wildlife crossing for a migrating herd of elk. And then as the climate changes and that herd moves northward, you know, you could actually pick up that wildlife crossing and disassemble it, and then reassemble it in the new location where the animals are migrating. So you know, being adaptive and flexible in the kinds of solutions that we're creating in thinking about climate change is certainly something that road ecologists are trying to do and need to do.

GROSS: As part of your research, you traveled to a few other countries, looking at what they're doing in terms of protecting animals from cars and roads. So let's talk about the U.K. What's going on there?

GOLDFARB: The U.K. has a lot of exciting road ecology projects. One of them is this initiative that used to be called Project Splatter, which was kind of a macabre name that I really liked. And then they changed it after some complaints to the Road Lab, a more anodyne version.

GROSS: (Laughter).

GOLDFARB: And, you know, what they're basically doing is marshaling the power of volunteer scientists, right? We're all out there driving around passing roadkill, and we're potentially data collectors, you know? And they've really harnessed that in the U.K. through this initiative called Road Lab, where, you know, you can use your smartphone to record the species and location of the dead badgers and hedgehogs and other creatures that you pass. And that's really valuable data.

And there are similar systems that exist in the United States. You know, California has a program called the California Roadkill Observation System run out of UC Davis. And, you know, all of that data that that program has collected, all of that volunteer-collected data, has helped to identify roadkill hot spots on the landscape that could conceivably be places for wildlife crossing.

So I think that's one of the exciting things about road ecology is that, you know, it's not like nuclear physics, you know? Yes, it's a fascinating, complicated discipline that requires real expertise, but it's also something that we can all participate in because we're all driving around. And, you know, most of us know what a skunk looks like. And we're part of the solution as well as part of the problem, potentially.

GROSS: Ben Goldfarb, thank you so much. This was, like, really interesting.

GOLDFARB: Thank you so much, Terry. Thanks for having me.

GROSS: Ben Goldfarb is the author of the new book "Crossings: How Road Ecology Is Shaping The Future Of Our Planet." After we take a short break, Maureen Corrigan will review a new dystopian novel set in the near future, when most plant and animal species have been smothered by a toxic smog. And the narrator is a chef. This is FRESH AIR.


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