Roadkill study demonstrates urgent necessity for safeguards

When an animal crosses a road, what factors determine its path – and survival?

Researchers from University of Mysore, the Zoo Outreach Organisation, and the Salim Ali Centre for Ornithology and Natural History (SACON), among others, monitored a single road running through the Western Ghats for an entire year to understand where roadkill occurred the most, and why. “Most studies look at the frequency of roadkill. While doing my research, I realised there was a huge lacuna in the surrounding parameters that are affecting roadkill, so we chose to consider those as well,” said S. Sushanth, a Fellow at the Zoo Outreach Organisation and lead author of the study.

Environmental factors such as plantations, water sources, terrain, and undergrowth were found to influence roadkill more than spatial and seasonal variation, the study found. 

The Western Ghats are an ideal canvas to study how changing landscapes affect wildlife. Despite accounting for just 6% of the country’s landmass, the Western Ghats – stretching from Gujarat to Tamil Nadu – are home to 30% of the country’s plant, fish, reptile, amphibian, bird, and mammal species. Of these, 325 species are globally threatened. The conservation and protection of these species is increasingly challenged by deforestation, urbanisation, and an expanding network of roads and railways.

Roads and railways – known as linear infrastructure – cut through forest habitats and fragment them. Changes in land use, such as the conversion of forest to agriculture or plantations, similarly transforms habitats, putting wildlife in closer proximity to human activity and risking higher mortality.

But not all animals are equally affected. The University of Mysore study, which looked at roadkill across a 50-kilometre stretch of a road cutting through Kerala’s Nelliyampathy Hills, found that reptiles and amphibians had the highest mortality from collisions with vehicles, followed by mammals and then birds. Relative to their abundance, such losses can be devastating for rare and endangered species.

Understanding animal behaviour could hold the key to mitigating such casualties, say experts.

Roadkill patterns 

Roads and other linear infrastructure can reduce the conservation efficacy of legal protections in the Western Ghats, because of the myriad threats they can introduce to the landscape, including the spread of invasive species.

A more direct impact, however, is collision with traffic. The University of Mysuru study recorded 330 dead animals belonging to at least 72 species along a stretch of the Nemmara-Nelliyampathy Main Road, near the Parambikulam Tiger Reserve. The same stretch was surveyed on 22 occasions between June 2023 and May 2024, to collect representative samples across seasons.

The overwhelming majority of those killed – 228 individuals – were reptiles. The worst hit were snake species like the Anamalai pit viper, Beddome’s keelback, the Nelliyampathy shieldtail, as well as species like the Indian garden lizard. “Reptiles’ high exposure to roads, their tendency to bask on roads for thermoregulation, their mode of locomotion, and their feeding behaviour make them particularly vulnerable. Additionally, snakes and other reptiles often evoke fear in people, leading to intentional killings on roads,” observed the study.

While most species killed were in the IUCN’s least concern list, 22 affected species were found to be endemic only to the Western Ghats, and five in particular were classified as Schedule I under the Wildlife Protection Act – endangered species that are given the highest levels of protection under law. These were the checkered keelback snake, rat snake, Southern hill myna, bonnet macaque, and leopard.

“What we didn’t expect was the outsized effect of coffee plantations on roadkill,” said Sushanth. Across all four taxa, coffee plantations – which flanked 37.6% of the surveyed road area – had the biggest impact on roadkill, over natural rainforest and tea and rubber plantations. Coffee plantations have mushroomed across the Western Ghats in recent decades, and are estimated to cover 25% of the region’s protected areas, according to one study.

“Most of the coffee plantations in the Western Ghats are converted forests, with similar ecological conditions,” said P. Balakrishnan, a scientist the Kerala Forest Research Institute, who was not involved in the study. “Several studies have shown that the diversity of mammals, reptiles, amphibians is almost the same as in forest patches, which could explain why they are found in abundance in these areas.”

When extrapolated over a year, the amount of roadkill along the 50-kilometre road alone comes to 5,490 animals annually. “Roads, while essential for human progress, must be designed and managed to coexist with natural ecosystems. Integrating conservation science into infrastructure planning can mitigate wildlife losses and foster resilience in vulnerable populations,” says the study.

Navigating roads

That reptiles and amphibians made up the biggest casualties from vehicular collisions in the Nelliyampathy Hills isn’t surprising. Several studies across the Western Ghats and other landscapes have thrown up similar findings. Deyatima Ghosh, an ecologist and Assistant Professor at Jain University, is studying why certain reptile and amphibian species are more vulnerable to road traffic in Andhra Pradesh’s Papikonda National Park.

“Altering a habitat can alter an animal’s behaviour,” said Ghosh. “If you see a common Indian toad, it’s a stumpy frog that doesn’t really hop. When it sees a car approaching, it freezes and plays dead, because that’s how they behave when there is a predatory threat. Other amphibians don’t necessarily behave the same way,” she explained.

In the Nelliyampathy Hills, the bicoloured frog saw the highest casualties among amphibians, followed by the common Indian toad. Species like the leaping frog and the Spinular night frog saw far fewer casualties by comparison.

On a trip through the Western Ghats in Karnataka’s Uttara Kannada district, Ghosh observed a king cobra crossing the highway. “It took three to four minutes for it to cross the road, but as soon as it touched the habitat on the other side, it disappeared in two seconds, without a trace. That indicates their mobility may be restricted when they’re on the road, which sheds light on added vulnerability,” she said.

Most infrastructure projects aimed at reducing collisions are designed keeping large mammals like tigers and elephants in mind, with less consideration to smaller animal groups. Installing piped culverts for amphibians and reptiles to pass through, or building fences along the road, could help mitigate impacts on these groups to a certain degree.

“A fence could help a common Indian toad survive, but perhaps not a bull frog, which is exploratory in nature and will likely to try to climb it,” said Ghosh, adding, “Mitigation techniques have to be catered to species behaviour, and a one size fits all approach won’t work.”

Designing mitigation infrastructure

Identifying roadkill hotspots alone isn’t enough to design a plan for mitigation, according to Bilal Habib, a scientist at the Wildlife Institute of India. Apart from animal behaviour, factors like road design, habitat specificity, and land use are added considerations for effective mitigation.

“Roadkill is an indicator of abundance. If there’s a higher number of a certain species that is killed, the ecological impact of its death has to be assessed against its abundance in a certain landscape,” he said, adding, “We have to be judicious about where to build large-scale mitigation infrastructures and for which species, because they’re built to maintain connectivity for 100 years. It requires a comprehensive topographical survey to understand where animals are choosing to cross, and why,” said Habib.

Over the last decade, India has experimented with building underpasses and overpasses across highways to aid safe animal movement and avoid collisions, in addition to adding more wildlife corridors around protected areas. In Pench Tiger Reserve, an underpass constructed on the NH44 in 2014 saw 5400 crossings by 18 large mammal species by 2020.

“Each successful crossing of wildlife through these structures can be referred to as a potential wildlife-vehicle collision avoided,” said Pramod Neupane, lead of Sustainable Infrastructure at WWF India. “Authorities and stakeholders are increasingly becoming more sensitised, and the adoption of such mitigation measures is evident in major infrastructure projects across the country. The present-day situation is definitely better than what it used to be a decade back.”

Since the first large-scale infrastructure project in Pench, crossing structures have been designed on highways across the country, including Assam, Maharashtra, and Delhi. Avoiding areas where there is potential for future conflict is key for longevity.

As road networks expand, the pressure they exert on already fragmented habitats will increase. Between 2014 and 2025, India’s national highways grew by 60%, from 91,287 km to 1,46,204 km. This pace equals 35 kilometres of national highway construction a day. “When existing roads are upgraded, there’s an opportunity to integrate these design requirements with a comprehensive mitigation plan. The challenge is with roads that are not upgraded, where it is difficult to retrofit, and animals remain exposed,” said Habib.

Banner image: A Beddome’s keelback snake after a vehicular collision. Image by Seshadri K.S. via Wikimedia Commons (CC BY-SA 4.0).