"Thousands of birds are about to fly or are already en route to their summer homes located in Central Asia and the Mediterranean region through war-ravaged Iraq," said Deepak Sethi, an expert on bird migration in the Indian hill town of Shimla.

He said younger birds follow the elders on journeys which are often thousands of miles long.

But the clouds could confuse the birds, who might lose their way and land elsewhere or even die along the way, he said.

"The migration of birds is a complicated procedure and... once disrupted it can lead to a lot of confusion and the birds may even get lost midway and eventually die," said Sethi.

Experts say the US-led bombing of Afghanistan in 2001 led to a similar disruption of age-old migratory routes.

Officials at the Pong Himalayan wetland in the picturesque Kangra valley, some 330 kilometres (200 miles) north of Shimla are worried that the clouds could disrupt the birds that visit it.

"We are particularly worried keeping in mind that the Pong Himalayan wetland... had a record 115,201 migratory birds this winter including over 60 species who are currently engaged in an arduous journey back to their summer homes. For many it could even be their last journey," said environmentalist Billy Malhans.

SPACE.WIRE