State of India's Birds 2023 report: What are the major threats to bird species in India?

The recently launched State of Indian Birds 2023 report draws attention to a distressing reality. Out of the 348 species that were assessed for Long-term Trends in the report, 60% of species show long-term declines. Furthermore, out of 359 species assessed for the Current Annual Trend, 40% of species exhibit a declining trend. The situation is particularly grim for migratory birds and birds of grasslands and other open habitats, wetlands, and woodlands, the report says.

But what are the factors underlying these trends? 

Monocultures

Monoculture plantations include commercial plantations of coffee, tea, areca nut, cardamom, palm, rubber, teak, or other species. These are created by large-scale clearance or modification of natural habitats like forests and grasslands. 

Bird species diversity and composition are impacted by a simplification of forest structure in monocultures, as well as by the accompanying management practices. Commercial monocultures are known to harbour fewer bird species than natural forests within the same biome. Plantations lack vertical and horizontal vegetation complexity because they maintain even-aged stands of a single tree species for ease of harvest. This usually leads to the loss of large-sized trees and a reduction in canopy shade and shrubbery. In addition to thinning and weeding, the use of herbicides and pesticides intensifies the adverse impacts on birds. Regular harvest operations reduce niches and resources for birds apart from creating physical disturbances.

Additionally, the report also highlights the faults in reforestation programmes across India and how ironically, they have also often created low-diversity monocultures. 

Environmental Pollutants

The report underscores the need to understand ‘pollutants’ in a broad sense, including pesticides, rodenticides, heavy metals, certain medical drugs, and plastics. 

Exposure to toxic chemicals during reproductive stages can affect fertility, egg formation, and eggshell thickness. Hence, can lead to impaired incubation and chick-rearing behaviours. All of this decreases hatching success and fledgling survival and increases the possibility of reproductive failure.

The report lists heavy metals (emanating from mining of metallic ores, refineries for metals, and thermal power plants), pesticides and veterinary drugs as some of the primary known environmental pollutants endangering birds. The continued and excessive use of pesticides in agriculture has impacted birds directly as well as indirectly by reducing populations of their invertebrate and vertebrate prey, the report informs. 

Furthermore, the report draws attention towards the increasing menace of plastics and their impact on bird populations- both through direct consumption (as in the case of seabirds) and the potential harm by microplastics.

Forest Degradation

Forest degradation manifests in various forms- logging of varying intensity, the spread of invasive species, high-intensity forest fires, fragmentation, excessive livestock grazing, biomass extraction, insect pests, and severe weather conditions. The results of SoIB report suggest that specialist bird species, including forest specialists, have suffered long-term declines due to these factors. 

Forest degradation affects biodiversity through reduced vertical and horizontal heterogeneity in plant form and composition. Complexity in vegetation structure is a crucial feature of forest habitats. Older forests tend to be more complex, and this in turn improves food and nesting resources for birds. Selective logging and chronic unsustainable biomass extraction could reduce the number of mature trees in forests, affecting species that depend on such trees. Loss of terminal branches and canopy due to firewood and fodder collection directly affects food availability for birds that forage in the canopy and on thinner branches.

The report also enlists studies in dry deciduous and tropical thorn forests of Rajasthan as well as Himalayan oak forests. They found that reduced canopy cover, tree height, and understorey density result in low bird diversity and composition. This is especially concerning in the backdrop of a 2012 report by the World Bank that estimates 41% of India’s forest cover to be in a degraded state, resulting in a possible loss of one-third of its forest productivity. The SoIB report further stipulates that between 2015 and 2021, an estimated 74,000 sq. km of forest in India underwent observable degradation. In the two years from 2019 to 2021, an estimated 9,000 sq. km of forest was converted into barren lands and scrublands.

Urbanization

Urbanisation-led diminishing of canopy cover, plant species richness, and vegetation heterogeneity is known to severely impact bird species richness in urban areas. As roads and built-up areas increase, the resulting loss and fragmentation of natural habitat for birds expose them to novel stressors such as elevated pollution levels, increased temperature, and increased density of free-ranging domestic predators like cats and dogs.

Additionally, urban noise is known to alter bird behaviour by compelling birds to sing louder, or at different frequencies, or, in the worst case, to abandon otherwise suitable habitats. Light pollution can confuse and disorient birds (particularly during migration), and increase their risk of crashing into buildings. During the day, glass facades of buildings are collision traps for birds that see the sky reflected on such surfaces. 

Energy infrastructure: Wind energy and power lines

Compared with conventional modes of power generation such as thermal power or large hydroelectric projects, wind and solar energy are considered ‘green energy’ and are promoted worldwide. However, there are growing concerns about impacts on wildlife, especially birds, from both the power-generating infrastructure (e.g., wind turbines) as well as the accompanying power lines. 

The report informs that wind turbines are installed in a wide range of landscapes including coastal areas, Western Ghats mountaintops, open arid lands, agricultural lands, and grasslands. The power lines criss-crossing these open habitats pose additional hazards for many birds. A case in point is the decline in the numbers of the majestic Great Indian Bustard (GIB). With 200 individuals left, almost exclusively in India, the species is listed as Critically Endangered and Schedule I (Wildlife (Protection) Act 1972. However, as per The Hindu report from 2021, about 15% of the GIB population dies each year due to collison with power lines (Wildlife Insitute of India estimates from 2020). This has also led to calls for taking the transmission lines underground, something which the Supreme Court of India also took cognizance of. Despite the court order, violations are widespread. 

The major impacts of wind turbines on birds include:  

1. Direct collision of birds with the rotating wind turbine blades  
2. Displacement (loss of habitat) of birds from the turbine area due to disturbance 
3. Barrier effects within habitats (obstacle to migration, or to other regular movements across feeding and roosting areas and breeding colonies) 

Additionally, transmission lines kill birds through two different mechanisms. For large-bodied species, collisions can be fatal, while for smaller species like passerines, the threat is from electrocution at distribution lines and pylons. These threats are known to have population-level effects, and sometimes even cause changes in migratory patterns.

Avian Disease

Globally, birds are hosts for an astonishing diversity of parasites such as Plasmodium, avian influenza virus and West Nile virus. The report stipulates that anthropogenic drivers such as land-use change, intensive livestock production, wildlife trade, and climate change are increasingly leading to the emergence and cross-species transmission of these pathogens.

The avian influenza outbreaks in 2020-2021 swept through many Indian States, causing mass mortality of wild birds is one scathing example. The report also draws attention to the lack of understanding of the role of infectious disease in the population dynamics of wild birds in India. It thereby underscores the need for long-term studies to better gauge the harm of these diseases in the Indian context.

Illegal Hunting and Trade

Live birds are trapped for the pet trade, or hunted for their derivatives such as meat, eggs, feathers, claws, beak, and casque. Further, superstitious beliefs have led to the illegal hunting of species like owls or Indian Roller.

Historically, India has been one of the major exporters of birds (live and dead) to the world. The report mentions that in the period 1970-80, some 14.8 million birds were exported, an average of nearly 13.5 lakh birds per year. In 1991, an amendment to the Wildlife Protection Act (1972) listed all bird groups under various schedules of the Act, and prohibited hunting and trade of scheduled species and their derivatives. With these activities having become illegal, monitoring the overall prevalence of illegal hunting is largely based on surveys of illegal markets and anecdotal reports of seizures. 

For instance, a survey undertaken in 1997 recorded some 64,500 individual birds of nearly 250 species in illegal trade in northern Indian markets covering the States of Haryana, Punjab, Delhi, Rajasthan, erstwhile Jammu & Kashmir, and Uttar Pradesh. 

Illegal hunting, in the form of shooting, poisoning, or snaring directly removes individuals from wild populations. Even when birds are caught alive for the pet trade, the stresses of transportation, crowded conditions, malnutrition and limited habituation lead to mortality rates of up to 90% due to disease, injury, food or water deprivation, the report mentions. Nevertheless, whether they survive or not, traded birds are removed from their source populations.

Climate Change

There are several ways in which changing climate affects birds.

1. Phenology refers to the timings of cyclical or seasonal biological events, such as migrations, egg flowering, and hibernation. The report states that phenological mismatches occur when the timings of annual events (e.g., migration, nesting, insect emergence) become asynchronous. As a consequence of this, there’s also a seasonal mismatch between birds and their prey. This has serious consequences on bird survival and reproduction, especially in migratory birds.

2. For sedentary birds, dealing with climate change will require rapid adaptive changes. The report refers to studies on Amazonian birds observed over a fifty-year period. The studies showed that all species underwent decreases in mean body mass, consistent with the expectation that smaller individuals— because they can lose heat more effectively—would be evolutionarily selected by warmer conditions.  

3. Higher temperatures also cause birds to alter their behaviour, making them more likely to seek shade and spend less time foraging, with negative impacts on survival and reproduction.  

4.  Bird species are also shifting their ranges to higher latitudes (i.e., away from the tropics and towards the poles) and in mountains, to higher elevations.

Additionally, the report warns of the emergence of new and dangerous interactions as a result of climate change. For instance, mosquitoes in Hawaii are colonising higher elevations, leading to the increased transmission of malaria in mountain birds that have never been exposed to malaria before. Climate change can also potentially push mountain species directly towards extinction as favourable conditions shrink at mountain summits.

Conclusion

This report analyses a range of threats based on the available scientific literature.  But at the same time, it also highlights the shockingly sparse literature on most threats and how that impedes work to identify linkages of threats with species decline. The report also underscores the need for systematic work over large spatial scales, focussed on specific threats, especially in  India, which is on a rapid development path.

The report puts the truth bluntly. With increasing world populations and associated demands for energy and food, the above-mentioned threats to bird populations will only increase. Climate change is likely to make matters worse. Careful research and timely action are needed if we are to reverse this trend, the report warns.

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