India witnessed a significant drop in the number of nearly 400 types of birds in the last 25 years, says a new exhaustive report on 867 bird species found in India.

While the count of the national bird, Indian Peafowl, has increased dramatically over the past decades, 50% of other Indian species of birds declined in the same period. The groups that show the greatest decline are raptors, migratory shorebirds and habitat specialists like Tawny Eagle, Red-necked Falcon and Indian Courser.

Released on Monday at the ongoing 13th Conference of the Parties to the Convention on Migratory Species at Gandhinagar, the report is based on more than 10 million observations contributed by 15,500 birdwatchers including scholars from 10 research organisations.

“Earlier, many conservation decisions pertaining to birds were not based on much evidence; this report helps to bring much-needed data to bear on these issues,” said Dhananjai Mohan from the Wildlife Institute of India, Dehradun.

The birds that suffered the maximum loss in the previous quarter century are White-rumped Vulture, Richard's Pipit, Indian Vulture, Large-billed Leaf Warbler, Pacific Golden Plover and Curlew Sandpiper.

The birdwatchers grouped the decline in two categories – a long term trend seen in the last 25 years and a short term pattern reported in the last five years.

As many as 487 species were monitored for the long term, out of which nearly half, 226 to be precise, did not reveal any specific trend. Among the rest, 52% have declined since 2000, with 22% declining strongly.

Similarly 677 species yielded short term data, out of which 531 species fall in the uncertain trend category. Among the remaining 146 species which showed an annual trend, nearly 80% are declining, with almost 50% declining strongly. In all, 101 species have been classified as of high conservation concern.

“We didn't go into the causes that could range from habitat loss and hunting to rampant use of pesticide. We hope the report would lead to such a research study,” Ashwin Viswanathan, one of the study authors from Nature Conservation Foundation, told DH.

However, there are few silver lines too. Not only the peafowl numbers have grown, the House Sparrow too has been found to be roughly stable across the country, though their numbers declined in the major cities including Bengaluru.

With their ubiquity and ecological importance, birds are excellent indicators of the state of the natural world. But currently, there are no national level bird counting exercise even though some of the states, particularly those harbouring wetlands, undertake an annual census on water birds.