AP PHOTOS: Tens of thousands of migratory birds have made this Indian lake their winter home

NAGROTA SURIYAN, India (AP) — Before the day breaks on a winter morning at the Pong Lake wetland in northern India, muffled honks of geese are heard in the distance.

A lone fisherman wrapped in a blanket rides his bicycle in the darkness, relying on his familiarity with the landscape. The air is heavy with water vapor and headlights of motorbikes zigzag across the swampy plain as more fishermen arrive, two on each vehicle. Before the sun rises, the fishermen's creaky wooden boats are specks in the distance.

In the soft light of dawn, a large flock of bar-headed geese at the water’s edge becomes visible. The geese seem to be stirring, and a few take off, noisily flapping their wings and honking. One flight soon triggers another and within a few minutes hundreds have taken to the sky flying east before settling on the grassy ground to feed on grains, roots, and other plants.

The geese are the flagship species of the wetland formed in Himachal Pradesh state in the mid-1970s after a dam was built on the Beas River.

The geese winter at the wetland, leaving their frozen homes on the Tibetan plateau and in Central Asia each year, tens of thousands of them crossing high mountain passes to settle in locations across India.

According to the Himachal Pradesh forest department, about 45% of the total bar-headed geese population spend the winter at the Pong wetland, more than anywhere else in the world except in their breeding areas.

In addition to 37 species of resident water birds, about 75,500 birds from 48 migratory species were recorded at the wetland last year.

Each autumn, water from the Pong reservoir is released to neighboring states and the receding water exposes a large area rich in organic matter. The grass and other vegetation that grows on this fertile bed provides food for the bar-headed geese and other grazing birds.

The number of geese wintering at the wetland varies each year, but it is difficult to directly correlate the numbers to climatic factors, according to Devinder Singh Dhadwal, a state forest officer and the author of a guidebook on the birds of the wetlands.

“The land made available by the receding water is the most important for the sustenance of the migratory birds dependent on grazing,” Dhadwal said.

Monsoon rains and temperatures affect the water levels in the reservoir, but it is mostly controlled by dam authorities.

After increasing for two consecutive years, the number of bar-headed geese at the wetland last year was about 25% less than the year before.

“Such decline is not immediately alarming unless sustained over at least five years,” said Reginald Royston, deputy conservator of forests in the Hamirpur wildlife division and officer in charge of the wetland.

The five-year average at the Pong Lake wetland is 40,000 to 45,000 bar-headed geese.