The Ramnagar Forest Division in Nainital district, Uttarakhand, has constructed its first ‘eco-bridge’ across Kaladhungi Nainital Highway (in Kala Dungri range). It is meant to save reptiles and smaller mammals from vehicular accidents while crossing the road, according to a report in December 2020. It is made from bamboo, rope, and grass.
What is Eco-bridge?
Eco-bridges (eco-ducts) are traffic-spanning bridges, tunnels, or underpasses (wildlife crossings) in forests and other wildlife areas which have been taken over by humans. They are being constructed in various places to ease wildlife movement and life in native habitats: for animals ranging from the gold monkeys and pumas in Brazil, jaguars in Mexico, deer and coyotes in the USA, water voles in London, to elephants in Africa, tigers and golden jackals in India, and bandicoots and wallabies in Australia.
Types of Eco-bridges
There are several types of eco-bridges like concrete underpass/overpass tunnels, or viaducts for large animals; canopy bridges for monkeys, squirrels, and other arboreal species; and amphibian tunnels or culverts.
The bridges are overlaid with planting from the area to give it the look of a forest area or a contiguous look with the landscape (decked with native flora). Undercrossings, which pass beneath highways to assist shyer and smaller animals, may be invisible to drivers.
There are aquatic corridors as well, linking waterways that have been separated by roads.
Importance of Eco-bridges
Animal bridges are seen as a step towards harmony between modernisation of human activities and animal life, which has been disrupted by these activities. Wildlife connectivity has been disrupted in many areas due to traffic of vehicles or occupational activities like logging, construction and so on. Wildlife habitats are becoming increasingly fragmented. Highways often cut animals off from resources they rely on for survival.
There have been numerous ‘road-kills’ around the world. Roaring traffic does not stop big mammals like moose and bears from crossing highways nor does it keep smaller creatures from being squashed by tyres. Accidents have a severe impact on people as well, taking into consideration human injuries and death, towing, vehicle repair, investigation of the accident by local authorities, and carcass disposal. The bridges are aimed to ensure wildlife connectivity, i.e., animals can migrate and move about as usual. Localised extinction can happen when populations cannot find each other, and this is especially true for low-mobility species in old-growth forests. Studies on a cross-section of native species’ deaths on highways in USA, Australia (bandicoots and wallabies), and Mexico (jaguars) show that wildlife crossings save lives, both human and animal.
Designing and Building Eco-bridges
Generally, engineers design the bridges to be inexpensive and natural-looking so as to not frighten the animals. While building eco-bridges/eco-ducts, it is necessary to know what the animal habitats are in the area, its topography, disturbance types, road length, and its curvature. The span and distribution of eco-bridges is determined by patterns of animal movement in the area.
Bigger bridges are used by animals like sambar, spotted deer, nilgai, wild pig, grizzly bears, elk, and moose. For animals that live in closed habitats like the barking deer, smaller bridges are built. Cougars and black bears prefer smaller and more constricted crossings with less light and more cover as their natural home is the forest, not the meadow. For carnivores like tigers or leopards, the bridge may be small or large. Underpasses tend to be more compact and are used more by smaller animals.
Fencing is installed leading up to the crossings in order to direct wildlife to the area—away from dangerous highway crossings and towards overpasses and underpasses. Rocks and brush piles are set up specifically to encourage the smaller animals to use the crossings.
Local project leaders identify routes/areas to document the wildlife and their travel patterns. For this, monitoring them is necessary through installed motion-capture cameras. It is ascertained as to where the animals generally cross and how their behaviour might be affected by the traffic. That information is used to find the place for constructing eco-bridges and eco-underpasses.
It is a lot easier and cheaper to build in these eco-bridges or eco-under-passes during road construction itself rather than to retrofit, as has been done in the USA and Canada.
Eco-bridges in India
About 50,000 km of road projects are on the cards over the next five to six years, as per a study by the Wildlife Institute of India (WII) in 2020. This is even as some highways are being upgraded to four lanes.
Three major sites have been identified by the National Tiger Conservation Authority, New Delhi, that cut across animal corridors. These include the National Highway 37 that cuts across the Kaziranga-Karbi Anglong Landscape, Assam, and State Highway 33 across the Nagarhole Tiger Reserve, Karnataka. One of the largest underpasses stretching 1.4 km is being built along the Madhya Pradesh–Maharashtra border. Other proposals include one on the Chennai–Bangalore National Highway, in the Hosur–Krishnagiri segment, near reserve forests for elephant crossings, and another in the Tadoba–Andhari Tiger Reserve in Chandrapur, Maharashtra.
In Ramnagar, on the Kaladhungi–Nainital Highway, an eco-bridge some 27m long and 1m wide has been built to avoid roadkills on the congested tourist route, especially of reptiles such as the monitor lizard. On NH 44, which intersects Kanha–Pench and Pench–Navegaon–Nagzira corridors in various sections, there are five animal underpasses and four minor bridges on a 6.6-km road within the forests. A 750-m-long underpass here is said to be perhaps the world’s largest underpass. Nearly 18 species have used these underpasses, including tiger, leopard, and golden jackal.
Nature Conservation Foundation, working in Annamalai Hills, Tamil Nadu, has constructed canopy bridges for arboreal animals, mainly lion-tailed macaques and Nilgiri langurs. In 2008, six bridges were built across a three-km stretch, the smallest one being some 10 m and the longest one, about 25 m. Building more of these corridors could ease the human-elephant tensions in southern India.
Global Scenario
Eco-bridges have been built in Europe since the 1950s. The Netherlands has 66 overpasses to protect its wildlife populations, mainly badgers, boars, and deer.
Eco-bridges are on the increase in North America the last three decades. There are 21 threatened and endangered species in USA whose survival is said to be threatened by road accidents. These include the key deer in Florida, bighorn sheep in California, and red-bellied turtles in Alabama.
Washington is constructing one of its first wildlife bridges, east of the Snoqualmie Pass in the Cascades, which began in 2015 over Interstate 90. Along with six underpasses built since 2013, these crossings are the first to allow elk, black bears, mountain lions, pika, salamanders, reptiles and even trouts to traverse what was once a near-impenetrable barrier of the road.
In places with elephant populations like Kenya and Bhutan, underpasses can be used to reunite members of fragmented herds.