Nepal's government has recently adopted guidelines to make infrastructure such as roads, dams and railway lines wildlife-friendly, following pressure from conservationists and NGOs.
Ninety out of 100 infrastructure projects in Nepal don't take the potential impacts on birds into consideration.
But not all wildlife have been included, with birds, especially those living in dense forests, likely to still be negatively impacted despite the mitigation measures.
The guidelines, issued in April, classify wildlife that could be impacted by infrastructure into five categories Small (such as tortoise, snakes and other reptiles and amphibians); small mammals (squirrels, rabbits, porcupines and civets); medium-sized animals (wild cats, dholes, hyenas and monkeys); big animals (rhinos, tigers, bears, deer and buffalo); and mega animals (wild elephants).
"Linear infrastructure such as roads and power lines severely impact birds, especially those that live in dense forests," or forest specialist birds, said prominent Nepali ornithologist Hem Sagar Baral. "However, 90 out of 100 infrastructure projects in Nepal don't take the potential impacts on birds into consideration," he added.
"As tigers and rhinos get killed in collision with vehicular traffic, authorities tend to focus on these mega faunas when designing wildlife-friendly infrastructure," Baral said. "Birds, who also suffer, mainly due to the fragmentation of their habitat, get little attention."
Fragmentation of habitat is one of the key challenges facing forest birds in the region, according to a recent study conducted in the Mai Valley in eastern Nepal, designated by BirdLife International as an Important Bird and Biodiversity Area. The valley is home to birds such as the rufous-throated wren-babbler (Spelaeornis caudatus), the spiny babbler (Acanthoptila nipalensis), and the hoary-throated barwing (Sibia nipalensis).
Under the study, lead author Aastha Joshi and her team, including Baral, compared the diversity of birds found in two forests in the Mai Valley: one contiguous (Hangetham Community Forest) and the other isolated (Maipokhari Religious Forest).
"We chose the Maipokhari forest habitat as a test case for isolated forests as the development of infrastructure around it caused the religious forest to be fragmented eventually and be surrounded by agriculture land," Joshi said.
The Hangetham Community Forest, by contrast, developed as a contiguous forest within the Panchthar-Ilam corridor of Nepal, connecting forests of two different districts, thanks to the active participation of the community in its conservation.
Climatic conditions were assumed to be identical for both forests, which are just 20 kilometers (12 miles) apart, Joshi said.
The researchers recorded bird sightings in the two forests from December 2019 to January 2020, and then again in March 2020 and March 2021 (curtailed due to COVID-19 restrictions). They found that the contiguous forest supported a significantly higher bird diversity than the isolated forest.
Measures such as building overpasses and underpasses and culverts don't necessarily help mitigate the impacts of roads on birds.
"As the continuous forest is surrounded by forests, it offers a wide range of micro-habitats, food sources, and nesting sites away from predators and competitors," Baral said. When the forest habitat is fragmented, the specific requirements of these birds can't be met, he added. That's why measures such as building overpasses and underpasses and culverts don't necessarily help mitigate the impacts of roads on birds, he said.
The team recorded a total of 1,138 individual birds belonging to 141 species throughout the entire study. The overall result showed a higher number of species in the contiguous forest (116) compared to the isolated forest (84).
"It has been well documented both in the [Indian] subcontinent and outside that the larger contiguous patches of forests support more bird diversity than isolated patches," said Indian ornithologist Rohit Jha, who has studied birds in both India and Nepal but was not involved in the recent survey. "The studies, including the recent one in eastern Nepal, add to our existing knowledge that only a subset of species found in larger forests is found in small patches," he added.
In the case of a forest spanning 600 square kilometers (230 square miles), Jha hypothesized, some bird species will only live within the innermost 200 km2 (77 mi2), "as they have developed and evolved to live in core forests away from human disturbance and edges of forests." These, Jha told Mongabay, are the forest birds that are most threatened in the subcontinent due to the fragmentation of habitat, he added.
Various studies have shown that forest patches in the Indian subcontinent are increasingly being fragmented due to various reasons, such as the development of roads, power lines and railways. A 2020 study found an increase in the number of forest patches and a reduction in the number of large patches (defined as covering more than 10,000 km2, or 3,900 mi2) due to linear infrastructure in India. High-tension power lines and major roads were the most common linear intrusions within forests, and 70% of the assessed protected areas had some amount of linear infrastructure passing through them.
In the case of Nepal, a 2018 study looking at forest cover in the country from 1930-2014 found a 75.5% reduction in dense forests, and an increase in the number of fragmented patches. A 2021 study looking at forest loss and fragmentation between 1930 and 2020 in the Asian elephant's range in Nepal's Terai plains found the area of the large forests had shrunk by 43% during that period, whereas smaller patches had increased several time over.
"As both Nepal and India are developing countries, there is a growing need for essential infrastructures such as roads and powerlines," Jha said. This means fragmentation will only increase in the foreseeable future, ramping up the threats to forest specialist birds.
Developers and policymakers in the region need to identify key contiguous forest patches and prepare plans to keep them intact.
Baral and Jha both agreed that important bird habitats should be avoided during the development of roads, dams, canals and railway lines. But if doing so isn't possible, mitigation measures should be adopted to minimize the impacts on biodiversity, including different bird species. They also called for wildlife-friendly infrastructure guidelines, such as the one issued by Nepal recently, to include birds.
Jha said that as part of the mitigation measures, developers and policymakers in the region need to identify key contiguous forest patches and prepare plans to keep them intact. "It is also necessary to ensure not just connectivity, but also functional connectivity, between forests, and not allow fragmentation, to save the specialist forest bird species," he told Mongabay. "The mitigation measures need to be designed to ensure that threats to birds are also accounted for from the starting phase of development projects."
This then needs to be followed up with effective monitoring, which is lacking in the Indian subcontinent, Baral said.
"When a development project is completed," he said, "we need to keep on effectively monitoring its impacts on biodiversity."
