Road ecology is a relatively new science, but it could shape wildlife and highways

Cliff swallows are a bird species that live all over the United States, but nearly all of them live on bridges. Scientists have found that, over recent years, their wings have grown smaller to adapt to being able to fly in tighter spaces and to be able to maneuver quickly in spaces where human vehicles are speeding along. “They have been shaped, subtlety, by the road,” writes Ben Goldfarb in Crossings: How Road Ecology is Shaping the Future of Our Planet.

His thesis is that about "40 million miles of road encircle the Earth" and that "when alien archaeologists exhume the rubble of human civilization, they may conclude that our raison d’être was building roads." Said another way by writer E.B. White: "Everything in life is somewhere else ... and you get there in a car."

Surprisingly, the study of "road ecology" was not even considered until a Harvard ecology professor wondered, in 1993, why researchers knew so much about Amazon rainforest ecology but nobody had ever thought to study the ecology of the roads running through the Amazon. The professor was initially laughed at but then the study of how roads were affecting plants and wildlife quickly took off and became a popular subject of study. 

Goldfarb notes:

"Constructed bridges for bears, tunnels for turtles, rope webs that allow howler monkeys to swing over highways without descending to the forest floor. On Christmas Island, red crabs clamber over a steel span during their beachward migrations; in Kenya, elephants lumber beneath highways and railroads via passages as tall as two-story houses. And road ecology has yielded more than crossings: we’ve also learned to map and protect the migrations of cryptic animals, to design roadsides that nourish bees and butterflies, and to deconstruct the derelict logging tracks that lace our forests."

One could actually claim that road ecology began back in 1924 when a young married couple of Iowa scientists started a game of counting roadkill as they travelled along the roads in what was likely a Model T. (That still sounds like a fun game with little kids, assuming they can stomach it.) One of their research papers noted: "America’s burgeoning need for speed had become one of the important checks upon the natural increase of many forms of life."

Ironically, many of our first roads were carved by wildlife who had used the pathways for many years. Native American footpaths and later Europeans with their "Good Roads" (for bikes!) activism cntinued the job of preparing for the as-yet-not-envisioned cars. By the 1920s, road building, with the likes of concretes and sealants and asphalt, was becoming serious business. Before then, roads were perceived as part of the natural environment, but now they were shaping the environment and conquering nature.

Daisy Buchanan ran over Myrtle Wilson in The Great Gatsby and that was about par for the course, as there were 23,600 car-related deaths in 1924 - a form of checking out that has always remained more prevalent than we seem to like to know about. But while road deaths for humans have nominally improved with better roads, deaths for animals have become worse with better roads. 

Speed was a major factor in the danger of roads to animals. As early as the 1930s, research pointed out that "below 35 miles per hour, cars seldom struck animals. Accelerate to 45, though, and they kill rapidly. Exceed 60 miles per hour, and you can figure on scoring a kill every 10 miles or less on most of the improved roads."

That early knowledge - almost prehistoric, at least in the sense of road ecology - fell away as those scientists died off, but the topic popped up again in the 1960s when deer populations began to explode in the nation’s suburbs. Now everyone knows how prominent the deer-vehicle collision problem is. We’ve all seen Tommy Boy, Get Out, and the episode of the Simpsons when the family hits a statue of a deer. There are nearly 60,000 people injured and more than 400 killed each year from collisions with deer. But deer were oddly never among the roadkill in those long-ago studies. That’s because suburbs created the perfect "edge" habitats that grew their numbers. The problem was that the suburbs had a very dangerous predator - speeding vehicles. Car interiors were especially dangerous places back then for coming into contact with deer, and after Ralph Nader wrote his book Unsafe at Any Speed, Congress made seat belts mandatory in 1966.

Long before suburbs, deer had formed a mental map and learned exactly which patterns to follow in their migration. That was never considered by engineers who blazed paths right across their territory, creating a situation that will likely never go away. The practice of using GPS collars to better understand the movements of migrating species didn’t begin until after the explosion of suburbia. As deer and other migrating animals began to be tracked better by scientists, it was discovered that only a small portion were becoming roadkill. Most starved because they couldn't get past interstates and barriers alongside them. They couldn’t get to their food sources and they starved en masse. 

Species don’t just rush from point A to point B when they migrate, they "surf the green wave," meaning they seek to find spots along the way where the snow has recently melted and plentiful fresh and colorful salads have sprouted. They will go from one of these zones to the next, often spending weeks in a single location along the way and attempting to migrate to spots where it is eternally early spring-like. 

In 2016, a biology study split animals into four groups: nonresponders like leopard frogs ignore roads and hop across no matter what’s happening on them, pausers like skunks get out onto roads and then hunker down on them, intelligent avoiders like grizzly bears stay away from any roads as much as possible, and speeders like deer evolved to outrun predators and that’s essential what they are doing trying to zip through cars on a roadway. When cars get going into the 70 and 80 mph range, deer finally give up and realize they don’t want to try to run through that, so rural country roads will usually have easily as much death for deer as interstates do. 

Another famous example of habitat destruction by road is Ventura Highway’s dissection of the Santa Monica Mountains - which are essentially the country’s largest urban park. Mountain lions need huge territories to survive and they are trapped there by the freeways. If they don’t get killed trying to cross, they tend to die at the hands of their parents. Young mountain lions leave their parents but the roads often keep them bouncing back in the their journey for independence, often leading to them to unnaturally return home and get killed by their parents. The area’s most famous lion, P-22, was recently hit by a car and succumbed to his injuries, but his celebrity is helping raise private (much of it celebrity) funding for an animal crossing above Ventura Highway. 

We always hear that 40,000 vehicle fatalities happen each year in the U.S., but that fatality number is even more stunningly around 3,600 around the world each day! The interstates, under the guise of helping spur "urban renewal," especially wiped out minority communities: Rondo in St. Paul, Overtown in Miami, Treme in New Orleans, and countless others. But now, cities like Syracuse, Oakland, Milwaukee, and Seattle are tearing down the viaducts that soar over cities and directing some traffic down to ground level or redirected away from cutting through the heart of places filled with people. "Creating a world that’s amenable to feet" is the dual goal of urban advocates and road ecologists. 

When COVID-19 hit, road-ecology scientists captured some startling data. California, Idaho, and Maine are states that have strong roadkill data, and the numbers dropped precipitously, with the researchers estimating a year of reduced travel "would save 27,000 large animals in those states alone." With traffic noise down, sparrows were found to sing more and actually sing better! 

Goldfarb concludes that we need to remake our roads as a massive public-works project. Some good news came along with the November 2021 infrastructure bill that included $350 million for wildlife crossings - the largest such investment of its kind in U.S. history. As the story progresses, this book will remain a valuable and surprisingly entertaining resource.