However, the bird experts have expressed concern over the noise and air pollution caused by mining and stone crusher units of Himachal Pradesh , set up close to the reserve. This has disturbed the habitat of birds which breed in rocky area, they say.

"In continuance with the trend, Ruddy Shelduck were spotted in the largest number, about 1,211 this year, followed by 567 Gadwall, 562 Eurasian Coot, 520 Green Winged Teal, 410 Eurasian Wigeon," said Sanjay Sondhi, founder president of Titli Trust.

"Around 327 species of migratory birds were recorded in the checklist," he said, adding that a pair of Pallas's Fish Eagles species were also spotted.

In the first record of Asan, three new species — Greater Painted Snipe, Taiga Flycatcher and Black Crusted Bulbul — were also spotted.

The estimation exercise was carried out by chief conservator of forests Dhananjai Mohan, founder president of Titli Trust Sanjay Sondhi and director Nature Science Initiative Raman Kumar recently.

Mohan told TOI that the habitat for Asan was further improved this year with grass cutting on shallow mud flats (flat patches in the middle of the river) which was included in the management plan of the area this year. "This gave more resting place to the ducks. It was interesting discovery that Pallas's Eagles preferred to sit on Mound of reeds as there is a fear of these heavy birds sinking in the wet reed.

Sondhi, however, expressed concern over constant air and noise pollution just on the other side of the water body disturbing the migratory birds' habitat.

"There are birds such as Red Water Lapwing, India Thick Knee and River Lapwing which are threatened species under International Union for Conservation of Nature. They breed in rocky area. Just because of the pollution and disturbance, they are unable to breed in such environment," he said.

However, come March, these migratory birds who come from Central Asia and Siberia will fly back to the region in North-East direction.