Highways bring people and cities closer together. Where once dusty wagon trails inhibited access to goods and services from other parts of the country, the rise of the freeway (and the car) provided unprecedented mobility for people – but, it turns out, not for wildlife.

In Los Angeles, the mountain lions of the Santa Monica mountains are trapped, hemmed in by busy oncoming traffic from the 101 freeway. “They’ll come right up to the freeway on both sides, turn around and leave. We know they’re not crossing,” says Jeff Sikich, a US National Park Service (NPS) biologist.

Sikich is part of a scientific team that, for more than a decade, has been studying the region’s last remaining large carnivore, the puma concolor (also known as a mountain lionor cougar). After trapping, radio collaring and monitoring 41 lions, Sikich and his colleagues from NPS have found that the 101 freeway is a major barrier to the mountain lion’s essential mobility. Over 60,000 GPS data points have shown that freeways act as movement barriers. Some of these majestic cats come up to the freeway and turn back, or worse, they attempt to cross and are killed.

In a bid to curb this ecological disaster, the National Wildlife Federation (NWF) has been heading Save LA Cougars, a massive initiative to build what could be the world’s largest wildlife crossing.

I walked with Sikich and Beth Pratt, California director of the NWF, one cloudy morning on a hilltop on Liberty Canyon road in Agoura Hills, Los Angeles.

The crossing wouldn’t be an unsightly road: it would be a lush, seamless extension of the wild beauty of the mountains

Home ranges near Los Angeles. The cougar known as P22 has the smallest known range of any mountain lion. Photograph: National Park Service

Sikich calls this an “island” of habitat. “These are the Santa Monica mountains, which are adjacent to the Los Angeles metropolitan area,” he says. “It’s roughly 710 sq km (275 sq miles) bordered by the ocean to the south, the 101 freeway to the north, the 405 freeway to the east and the Oxnard agricultural fields to the west.

“We need to make sure that any animals north of here can come down, and that animals born here can leave so as to not have to breed with their father, if they’re female. Young males, too. Most males born here end up getting killed either attempting to cross the freeway or fighting with an adult male.”

As we stood on the hill, Sikich and Pratt took me through an imaginary tour of the future wildlife crossing. If completed as they both hope, the crossing wouldn’t just be another unsightly cemented roadway or a gloomy tunnel beneath the freeway: it would be a lush overpass, spanning 10 freeway lanes and 140ft of asphalt, laden with native shrubs and plantings. It would be a seamless extension of the wild beauty of the Santa Monica mountains, connecting it to the natural green spaces of Simi Hills, the Santa Susana mountains and the Los Padres national forest, where the nearest other healthy population of cougars resides.

The wildlife crossing would establish a natural two-way street where animals could traverse in safety, allowing immigrant cougars from other home ranges to wander into the Santa Monica mountains and vice versa.

Over the course of NPS’s research, 13 cougars have been struck and killed by vehicles. In the years that the scientists have maintained records, only a few have survived, including P-22, the mountain lion of Griffith Park, who gained international fame after crossing two busy freeways, the 405 and 101. Unfortunately, P-22’s lair in Griffith Park also hems him in the middle of a network of freeways, cutting him off from his dating pool.

It’s a classic case of being stuck between a rock and a hard place. These big cats can’t stay in the Santa Monica mountains. If they do, they continue to face life-threatening consequences.

“Mountain lions require a large amount of space. One male can cover all of these mountains as their home range,” says Sikich. “They’re solitary animals. Adult males can kill other males within their territory.” A typical home range is around 200 sq miles for adult males and 75 sq miles for adult females. The Santa Monica mountains are just 225 sq miles. In other words, “This town ain’t big enough for the both of us” might as well be these lions’ mantra.

A mountain lion known as P14 in tree. Photograph: National Park Service

The NPS has, so far, documented four cases of in-breeding where fathers mate with their daughters; a male killing two of his offspring and a mate; and his son killing two of his brothers. This precariously low genetic diversity could lead to birth defects such as holes in the heart, decreased sperm counts and, eventually, to a halt in reproduction.



Only one mountain lion is killed every year, which may not seem consequential, but that’s one too many, says Pratt. “One or two lions dying a year, that’s not a lot, but for this population it is. You take out one or two male lions bringing genetic diversity in and this population could collapse.”

The crossing wouldn’t just be good for cougars, Sikich says. It spells benefits for a wide range of wildlife, including bobcats, coyotes, deer and even smaller species such as birds and lizards. “Vegetated overpasses can act as a guiding line function for birds to safely cross,” says Sikich.

The construction of this crossing would help sustain the region’s wildlife population – a particularly pressing concern since this is a region considered to be one of 35 biodiversity hotspots in the world. A term originally defined by environmentalist Norman Myers, and further expanded by Conservation International, hotspots represent just 2.3% of the Earth’s land surface, yet support nearly 43% of birds, mammals, reptiles and amphibians.



NWF is looking to raise about ($4m) £2.6m for the planning and design of the crossing, as well as an endowment for continued funding for Sikich and other researchers. So far, they have secured $1.1m of these funds, thanks in large part to a $1m grant by the State of California Coastal Conservancy. NWF has further plans to launch a “match the million” fundraising campaign, as well as a text-to-donate initiative. Pratt hopes everything will be in place for construction to start by 2018.

Biodiversity hotspots represent 2.3% of the Earth’s land surface, yet support 43% of birds, mammals and reptiles

A freeway cuts through mountain habitat. Photograph: National Park Service

Save LA Cougars may be the most prominent initiative to try to add much-needed natural connectivity through and across urban settings, but the 101 freeway isn’t the only one endangering animal ecosystems. Roads ease human passage, but unintentionally hamper ecological systems by fragmenting formerly seamless habitats. In response, countries around the world have built wildlife crossings of their own.

The Netherlands has built more than 600 wildlife crossings that ferry wild boar, red deer and endangered European badgers to and fro, including Ecoduct De Woeste Hoeve over the highway A50. Canada’s Banff National Park in Alberta boasts 44 wildlife crossings that ferry bears, moose and elk over the Trans-Canada highway. Smaller crossings have been built in the United States, protecting spotted salamanders in Massachusetts, desert tortoises in California and mountain goats in Montana.



These valuable structures can’t be built soon enough. Species have been disappearing at 50-100 times the natural rate and as many as 34,000 plant and 5,200 animals species face extinction. The loss of one species is not just a sad news item; it could mean the loss of a lynchpin in the ecosystem.



According to the International Council for Local Environmental Initiatives’ Cities Biodiversity Centre, cities are expected to triple in size to an estimated 465,000 sq miles by 2030, putting even more pressure on biodiversity. With that expansion, we can expect to see more fragmentation and loss of natural habitats.

“We used to think that putting aside these protected natural spaces is enough,” says Pratt, “but as we’re finding in the last 50 years, that’s not how it works. Animals need to move, even in urban and suburban landscapes. They need ways through cities and around cities. That’s why urban wildlife conservation is so critical, not just for mountain lions, but for all wildlife, birds and lizards.”

In a recent study, published in Current Biology, researchers noted that thousands of threatened species are helping to keep the planet’s ecology stable. Mussels and clams help keep waters clean; woolly monkeys and red-footed tortoises help grow forests; and even evil-looking vultures help curb disease. Saving nature actually means saving ourselves.