New Delhi, India - A new study claims that India's bird population has seen a "sharp decline" in the past two decades and in some cases, the drop is even "catastrophic".

"This assessment of nearly 867 Indian species makes it very clear that our birds are in overall decline, in some cases catastrophically so," according to the report released on Monday during the continuing United Nations 13th Conference of the Parties to the Convention on the Conservation of Migratory Species, in the western state of Gujarat.

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"Many more species show a downward trend than an upward trend," it said.

The study called State of India’s Birds 2020, put together by nearly a dozen institutions and numerous citizen scientists, is the first comprehensive assessment of the distribution range, trends in abundance and conservation status for most of the bird species in India.

The data for these birds were collected through the citizen science app eBird - a global crowdsourced database that has real-time data on the distribution and abundance of birds - which received a record 10 million entries by approximately 15,500 citizen scientists and professional birdwatchers.

Vulture population crashed

The report said the assessment was based on three indices; two are indices of change in abundance, long-term trend (ie over 25+ years) and current annual trend (ie over the past five years); and the third is a measure of distribution range size.

It claims that more than 100 species of birds exhibit a decline in the long and short terms, raising their threat of extinction.

"Using these three indices together with the International Union for Conservation of Nature (IUCN) Red List, each species was classified into categories of conservation concern for India: 442 into low concern, 319 into moderate concern and 101 into high concern," the report states.

Of the 261 species for which long-term trends could be determined, the report said, 52 percent have declined since the year 2000, with 22 percent declining strongly.

Species that have suffered the highest declines include white-rumped vulture, Richard's pipit, Indian vulture, large-billed leaf warbler, Pacific golden plover and curlew sandpiper.

The report states that since the 1990s, the populations of several species of vultures have crashed.

During this time, bustards and other specialist grassland birds have also experienced clear declines and some species that are popular in the bird trade, such as the green munia, are at dangerously low abundance, it said.

'A wake-up call'

Suhel Quader, a scientist with Nature Conservation Foundation, which took part in the study, told Al Jazeera that the aim of the study was to "assess the overall health of India's birds".

He said that in the absence of an information base, people used to imagine that everything was fine. "This (study) is a wake-up call for everyone that things are not fine and we really need to act," Quader said.

"Now, we have the database to track the status of our bird population more or less year on year. So we have, in a sense, an early warning system to understand the changes in bird numbers."

Birdwatchers say the report is "alarming" and needs to be taken seriously.

"This is empirical data. This is not some conjecture that people have," said Misha Bansal, a bird watcher. "The study needs to be taken very seriously."

The report said that the conservation action must be taken immediately to identify causes of decline and implement measures to halt and reverse the trend for these species.

"These species must be carefully monitored to rapidly detect and act upon signs of continuing decline," it said.

Pankaj Gupta, another bird watcher and member of the Delhi Bird Foundation, urged the government to protect bird habitats.

"Unless they will protect the habitat, nothing much can be done. The government has to make more national parks, wildlife sanctuaries and protect as much as they can," he said.

"With too much pressure of development, environment takes a back seat," he said.

In encouraging news from the study, a total of 126 species of the 867 assessed, including the house sparrow, Indian peafowl, Asian koel, rose-ringed parakeet and common tailorbird, appear to be stable or increasing in the long term.