And though the Yamuna, with high pollution, does not attract many migratory birds, Yamuna Biodiversity Park, on the upper reaches of the river at Waziarabd, is now hosting Siberian Red Crested Pochards, rare in these parts. Other migratory birds who have arrived this winter are Pintails, Gadwall, Pygmy Goose and Shovellors.

Experts have, however, pointed out that the only birds that are likely to be found in the polluted Yamuna below Wazirabad are river gulls, which feed on insects that thrive in sewage, and nematodes, microscopic worms that are found in leafy vegetables. This, because coliform levels at various spots in the river jump just after reaching Wazirabad. Just before Wazirabad, levels are at 160,000 parts per 100 ml. Just after Wazirabad, the figure touches 230,000. Downstream from Najafgarh drain, the figure is at 950,000. Downstream from Okhla Barrage it is at a staggering 1200,000. The figure gets lowered in Agra at 530,000.

“The high pollution in the Yamuna is the reason why birds no longer migrate here... though traditionally birds used to fly in,” says Dr Faiyaz Khudsar, scientist-in-charge, Yamuna Biodiversity Park. Interestingly, the Red Pochard, perhaps due to pollution, only migrates to the upper reaches of the Yamuna.

“The Red Pochard is an indicator of the good quality of a habitat. It is a rare bird which only migrates to the upper reaches of the Yamuna. This year, a handful of Red Pochards have arrived in the Park. This is probably the only place in Delhi where Pochards come and stay for an extended period of two months. You are not likely to find it commonly in Okhla Bird Sanctuary either,” he says.