When the toad couldn’t cross the highway

As highways get broader and better, making travel easier, they have also become a hindrance for Earth’s smaller denizens


Photo: Preeti Sharma
Photo: Preeti Sharma

New Delhi: When the Union finance minister proposed Rs.55,000 crore for roads and highways in his annual budget, few quibbled—there is general consensus that the country needs a good network of roads.

If only toads could speak.

As highways get broader and better, making it easier for us to travel, connect and move things around, they have also become a hindrance for the planet’s smaller denizens. They are a barrier for wildlife to move from one forest patch to another or for slow-moving species that live in and around human habitations.

Today, a toad (or a frog) is unable to hop its way across the highway. Once a regular visitor to our lawns and gardens, especially during the monsoons, the Common Asian Toad—that warty, jumpy, diminutive amphibian—is hard to spot these days. Frogs and toads, nature’s unsung pest controllers, have long been disappearing from the Indian urban landscape (bit.ly/1aNQfHl).

Now a new Indian study* (see below) shows that toads are unable to cross a national highway (NH) not just because of the burgeoning size of the highways but also due to factors such as vehicular traffic.

The study, a collaboration between the Laboratory for the Conservation of Endangered Species (LaCONES), Centre for Cellular and Molecular Biology (CCMB) and Wildlife Institute of India, was funded by the Department of Biotechnology and WWF India.

It is the first telemetry study of amphibians in India—aimed at giving scientists an understanding of the effect of linear barriers on the common Asian toad in a human-dominated landscape. Radio-telemetry has proven to be a valuable tool for determining amphibian activity, dispersal and migration patterns because amphibians are often secretive, nocturnal and sometimes move long distances in short periods of time.

The study concentrated on Krishnan Kovil, a small village located on the eastern slopes of the Western Ghats in Virudunagar district of Tamil Nadu. The NH208, an 11m-wide tarred road with no median barrier, runs through the village. The researchers, who conducted their study between December 2014 and December 2015, also looked at tarred roads of 4-6m width and gravel roads in the village.

The study is also the first of its kind in the country to try and understand the underlying mechanisms that impact wildlife populations due to “linear intrusions”—or roads.

“Toads and frogs are some of the most prolific breeders and have the capacity to endure and recover from population fluctuations. However, the species cannot cope with the changing landscape, especially fragmentation and loss of habitat, linear barriers such as roads, railways, power lines, pipelines being one of the potential causes for amphibian decline. Their inability to cope with ‘modern’ threats is difficult to understand by biologists around the world,” says Karthikeyan Vasudevan, senior principal scientist, LaCONES, CCMB, Hyderabad.

As the country’s human population increases—India will be the world’s most populous country by 2022, according to the UN—the road network has grown rapidly.

Already the country is home to the second largest road network in the world. According to the ministry of road transport and highways, India has 4.87 million km of roads. National highways account for 1.9% of the total road network and are expected to reach 100,000km by the end of 2017.

“This rampant expansion of road network has its consequences on wildlife through mortality and creating barriers for movement. We need to understand this in order to mainstream conservation efforts in large-scale infrastructure developmental programmes,” adds Vasudevan.

The conflict between roads— the most visible aspect of India’s growing physical infrastructure—and wildlife has intensified in recent years.

The expansion of NH7, which skirts the Pench National Park in Maharashtra, for instance, was a heated topic of discussion at the National Green Tribunal. Wildlife conservationists vehemently opposed the expansion as it passes through a critical wildlife corridor between Pench and Kanha national parks.

Wildlife corridors are ecological necessities for the dispersal of species and their gene pool.

According to conservationists, expanding roads and highways are slowly dividing critical wildlife habitat into small isolated islands where they have to find food, establish territories, reproduce and disperse.

The effects of roads on the wildlife population are not just limited to India. Elsewhere, the issue is widely studied and has led to the emergence of a new discipline in science called road ecology. Road ecology research aims to quantify the ecological effects of roads, and looks into how to avoid, minimize and compensate for their negative impact on individuals, populations, communities and finally, ecosystems.

Worldwide, there are an estimated 750 million vehicles travelling on approximately 50 million km of public roads, with road networks and traffic volumes still increasing in eastern Europe, China, India and Latin America, according to a paper published in 2011 in the online journal Ecology and Society**.

“Roads and other linear infrastructure are a major cause of habitat loss, fragmentation, and degradation and are ubiquitous in most landscapes around the world,” it says.

“Linear infrastructure is important for society because it provides connectivity for people. However, linear infrastructure also exerts significant negative effects on adjacent habitats, wildlife populations, communities, and ecosystems., the paper adds.

One victim is the common Asian toad, one of the most widespread species of toads with no protection status, scientists say.

“It may be non-endemic, carrying a ‘least concern’ tag in conservation literature, yet there is evidence of population bottlenecks taking place in southern India due to roads. The idea (of the Indian research project) was to see how a changing landscape affects the toad’s movement and abundance,” says Vasudevan.

To study the movement of these toads, researchers deployed a dozen Very High Frequency transmitters on a rotational basis in the breeding (heavy rains) and non-breeding (less or no rains) season.

These lightweight transmitters were fixed onto the toads with a harness fashioned from a Teflon tube, elastic and a cotton thread. After several experiments and trials the researchers decided on the ‘waist belt method’ which caused the least disturbance to the animal, says Preeti Sharma, research fellow in the project.

The type of harness decided, researchers picked up toads at varying distances from NH208. “It was hypothesized that the individuals near a highway have limited movement compared to those away from the NH,” says Sharma.

Equally, tracking the tiny toads was a challenge for the team. The toads are well camouflaged in their microhabitats—under rock and brick piles, in drains pouring sewage outside homes, in deep quarries, water tanks and garbage dumps, under thick thorny vegetation or in muddy water.

“During the non-breeding season, the toads did not show a lot of movement due to excess heat and unavailability of enough and clean water sources. Yet, a male toad showed movement of 330m on a rainy night. This was the maximum movement recorded for the non-breeding season. It was interesting to note that the toad returned after three days to the same rock pile from where it had started,” says Sharma.

The male toad did not cross the highway. However, it did cross a village tarred road (width 3-5m) and several gravel roads. The movement was not towards the NH—it was parallel to it.

For Vasudevan and Sharma, this indicated strong “site fidelity”—an academic term for the tendency of an organism to stay in, or return to its home area, which is an important aspect in the conservation of amphibian species.

Amphibians have been generalized and viewed as organisms with poor dispersal ability. Being considered less charismatic than some other species and types, they have always received a half-hearted conservation attention. No prizes for guessing who gets the bigger slice of the conservation cake—tiger or toad.

But the fact remains that with the current scale of landscape alteration and laying of the roads network, the population of toads is facing large-scale mortality in India. The need to connect people through roads is increasingly isolating the amphibian population, which in turn is affecting their population viability as the connectivity of breeding spots gets disrupted.

Radio-telemetry has proven to be a valuable tool for determining amphibian activity, dispersal and migration patterns because amphibians are often secretive, nocturnal and sometimes move long distances in short periods of time. The movement of toads in the breeding season is found to be higher than in the non-breeding season.

“The results of the study so far reveals that NH is a potential barrier to the amphibian population. The toads are avoiding NH but other road forms like the village metal roads and the gravel roads are still permeable to toad movement. Also, it was found that abundance of toads near to the NH is less as compared to the sites away from NH,” says Sharma.

The findings from this study have important implications for our growth of linear infrastructures. Ecosystems functions are lost when species are lost in the landscapes.

This is the first in a series on how infrastructure projects are affecting natural habitats.

* Effect of linear barrier on movement ecology of common Asian toad (Duttaphrynus melanostictus), (Field work December 2014-December 2015). Detailed analysis for second phase (breeding season) of the study is still under progress.

** Effects of Roads and Traffic on Wildlife Populations and Landscape Function: Road Ecology is Moving toward Larger Scales, Ecology and Society (2011).

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