Although the number and variety of birds has plummeted over the last two decades, several foreign species continue to visit National Zoological Park during winters.
From about 5,000 migratory birds spread across more than 10 species in 1980s, the number at the zoological park, also known as Delhi Zoo, has fallen to 500-odd birds belonging to five-six species.
For zoo officials, Pintail Duck, Shovellar duck, common teal, dab chick (all coming from Siberia and/or south-east Asia) and coot are "true migratory birds". This is because, there are local migratory birds (from within India), like painted storks, that are abundantly found at the Delhi zoo also.
"Several true migratory birds like Siberian crane, brahminy duck, mallard, red-crested pochard and white stork have not visited the Delhi zoo over the last few years," Riaz Khan, the zoo's curator (education), said. "War, atmospheric pollution, lack of food, global warming and hunting by humans are few causes that result in declining numbers."
However, local migratory birds arrive in droves to Delhi and stay for several months.
The advanced party of these birds arrived around October-end. As the temperature dips, more birds arrive with maximum presence noticed during January to February.