Global climate impact has delayed the arrival of late winter migratory birds on river Yamuna here, according to ecologist T K Roy. As per latest field survey mainly on upper Yamuna River, it recorded following seven migratory water bird species:- Great Cormorant: migrates from east and southeast Asia Black-headed Gull, migrates from central Asia Pallass Gull: migrates from central Asia Common Sandpiper, migrates from north and east Asia Grey Wagtail, migrates from Eurosiberia region White Wagtail, from Eurasia region and from central Palearctic region, he said. River Yamuna passing through Delhi 22 km length, a riverine wetland has converted into most polluted, degraded and disturbed wetland habitat for aquatic biodiversity especially for water birds due to pouring 21 sewage drains includes the largest sewage drain Najafgarh Drain into the river.  Moreover, public throws huge amount of biodegradable and non-biodegradable garbage into the river, continuous urban development on the riverbank and over the river, he said.  Also, seasonally dry riverbed is used for seasonal cultivation, encroachment of the riverbed and floodplain and several other activities fluctuates, decreases species diversity, according to Roy. Having shortage of wetland habitat in Delhi but being under the Central Asian Flyway still seasonal some migratory water birds of lesser species diversity has arrived on Yamuna whereas no migratory water birds arrival so far on the other wetlands and besides Delhi in Noida, he said. 

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