The birdwatchers claim to have spotted migratory water birds such as Black-tailed Godwit, Ruff, Common Teal, Common Redshank, Wood Sandpiper, Western Marsh Harrier and Pied Avocet. Even Indian resident migratory water bird species such as Little Tern and Whiskered Tern and terrestrial birds such as Bluethroat and Clamorous Reed Warbler have been sighted since August.

“This year because of good monsoon rain all over the country, freshwater wetlands, including lakes, marshlands and tanks, have revived and it has resulted in early arrival of several winter migratory bird species,” Ecologist TK Roy, who is the Delhi state coordinator of the Asian Waterbird Census, Wetlands International South Asia, said.

The Black-tailed Godwit – an International Union for Conservation of Nature Red Listed (NT) category of Threatened Bird Species – migrates in winter from North Asia to South Asia, including the Indian sub-continent. Ruff, Common Teal, Common Redshank and Wood Sandpiper, too have the same migration route. Western Marsh Harrier migrates in winter from western Europe to south Asia while Pied Avocet comes from Central Asia to southeast and south Asia. Bluethroat and Clamorous Reed Warbler in summer stay in the Himalayas and in winter migrate to widespread plains.

The Okhla Bird Sanctuary — spread over an area of four square km on the Yamuna — is a haven for water birds and a favourite among birdwatchers. After the construction of Okhla barrage and the resulting lake in 1986, the bird watching activity increased.

“Due to continuous biotic pressure and several human threats to this urban sanctuary, bird diversity and population has been under threat. The Ministry of Environment Forests and Climate Change’s notification of 100m eco-sensitive zone around the sanctuary is not effective to protect the habitat of the sanctuary. However, this is a welcome sign,” Roy said.

Another birdwatcher Wing Commander Vijay Sethi said sighting of these migratory birds in August is significant. “Normally you can see these arriving in Okhla in the first week of September. August is a bit early. The volume of rain this year has definitely made it cooler and that can be the reason behind this early arrival,” Sethi said.

Sohail Madan, centre manager, CEC-Bombay Natural History Society, Asola-Bhatti Wildlife Sanctuary, feels climate change is the reason behind this early migration. “The migration pattern is getting erratic every year. This summer we saw Greater Racket tailed Drongo. It has never before been sighted in Delhi or other parts of North India. It is usually found in Southern peninsular India. Heavy rain this season might be another reason for this early arrival,” Madan said.