The first-of-its kind analysis was carried out by scientists from ten research and conservation organisations across India, using a massive database of over 10 million observations uploaded by 15,000 birdwatchers on the online platform, e-Bird.
Out of total 867, the researchers could study the long-term trends for only 261 species due to lack of data, out of which 52% have declined since the year 2000, and 22% have declined strongly. In all 43% of species showed a long-term trend that was stable and 5% showed an increasing trend.
In the current annual trends for 146 species, nearly 80% are declining, with almost 50% declining strongly. The report identifies 101 species to be of ‘High Conservation Concern’ including the open-country Raptors (vultures) and migratory shorebirds which continue to face the most catastrophic declines.
“Till early 1990s, none of the nine species of Indian vultures had any conservation issue. But after 2000, four of them became critically endangered and now, one of them is endangered and three are nearly threatened. These scavengers are bio-indicators and their dwindling numbers do not augur well for our environment," said Dr Vibhu Prakash, Principal Scientist at Bombay Natural History Society (BNHS).
Other species that fared poorly included sea-birds- Gulls and terns, forest and grassland specialists, long distance migrant like Richard’s pipit, large-billed Leaf Warble, Pacific Goldern Plover, Curlew Sandpiper and Western Ghats endemics. Birds that eat invertebrates have declined as a group.
“Most specifically, it is the birds which depend on forests, grasslands and open-habitats which seem to be declining at a faster pace, including those endemic to Western Ghats. We need urgent efforts to monitor their habitats and investigate these changes, so that necessary steps can be taken," said Ashwin Viswanathan, researcher at Nature Conservation Foundation (NCF).
The 12 Western Ghats endemics included in the analysis showed a dangerous long-term decline, being almost 75% less in their abundance index today than before 2000, including some common species like Crimson-backed Sunbird and Yellow-browed Bulbul.
While the report does not delve upon the reasons for the decline, researchers say, the conversion of natural habitats for primarily human, hunting and trapping for consumption and the pet trade, environmental toxins like the veterinary drug diclofenac remain some of the threats for birds worldwide.
But as half of the bird species dwindle in numbers, the report shows, the population of House Sparrow has been fairly stable overall during the last 25 years, along with India’s national bird, the Indian Peafowl which showed a general increase in the long-term, against the common perceptions about their decline.
“This the first time, that such country-wide assessment was done for birds in India, so we did not have a base-line, but in case of sparrows, we found the numbers to be declining only in urban areas, especially metro cities. Probably, sparrows have not been declining in the country as a whole, which is why we need more such monitoring efforts," said Dr Viswanathan.
Apart from House Sparrow, researchers found 125 other species to be stable or increasing in the long term, including the Asian Koel, Rose-ringed Parakeet and Common Tailorbird. According to researchers, many of these species have adapted well to human-dominated habitats even though they are not obligate human commensals.
“Our birds need immediate conservation attention before their numbers reduce further," said Dr R Jayapal, Senior Principal Scientist from Sálim Ali Centre for Ornithology and Natural History (SACON), Tamil Nadu, calling for need to step up monitoring and conservation efforts.