Thousands of migratory wader birds are continuing to linger along the Mumbai Metropolitan Region’s coastline well beyond their usual departure window, leaving birders and ornithologists puzzled.
Large flocks of Tibetan Sand Plovers, Greater Sand Plovers, Curlew Sandpipers, Ruddy Turnstones and Terek Sandpipers, along with Lesser Flamingoes, were recorded this weekend across the mudflats and wetlands of Thane Creek. Their prolonged stay has coincided with an extended summer and a delayed onset of monsoon conditions.
While the presence of flamingoes can be linked to erratic weather patterns, the continued stay of other long-distance migratory waders has surprised experts.
“Most of these birds breed in far-flung regions stretching from the Himalayas to the Arctic. By now they should have reached their breeding grounds and many would already be raising chicks,” said Raju Kasambe, ornithologist, Maharashtra state coordinator of the Asian Waterbird Census and founder of Mumbai Bird Katta.
During a visit to the TS Chanakya wetland on Sunday, Kasambe counted around 700-800 waders. The majority were Tibetan and Greater Sand Plovers, accompanied by smaller numbers of Curlew Sandpipers, Ruddy Turnstones and Terek Sandpipers. Many of the sand plovers were already in their striking breeding plumage, indicating readiness for courtship and nesting.
Adesh Shivkar, founder of the Mumbai Birdwatchers Club, also reported unusually large numbers of migratory waders that appeared to have delayed their departure.
Lesser Sand Plovers, Curlew Sandpipers, and a Terek Sandpiper forage in shallow wetland waters. (Photo: Dr Raju Kasambe)
According to Kasambe, the waders begin leaving India’s west coast by March, timing their migration with changes in daylight that signal the arrival of spring in their breeding grounds. By late May, most have usually left.
“These birds undertake journeys of several thousand kilometres. The increase in day length acts as a trigger for their return migration. This year, however, many appear to have remained here even after the summer solstice, the longest day of the year,” he said.
The birds spend the northern winter in India and begin heading back to breeding grounds across Mongolia, Tibet, China, Central Asia and, for some species, Siberia, the Arctic regions of Russia, Finland and beyond. The return journey is driven largely by the seasonal availability of insects and other food sources in those regions.
Only a small number of juvenile, hurt, old or weakened birds are known to skip migration, Kasambe said, but such individuals do not account for the large numbers being observed this year.
The delayed presence of flamingoes is easier to explain, he added. Lesser Flamingoes breed in the Rann of Kutch in Gujarat and their movements are closely linked to water availability.
“Last year’s monsoon extended well beyond its normal duration, which meant wetlands retained water for longer and the flamingoes stayed back. With the monsoon now arriving, they are likely to begin moving towards their breeding grounds,” Kasambe said.
Unlike flamingoes, which can reach Kutch in a single overnight flight, many wader species face far longer journeys that can stretch over weeks.
Their overstay might mean they are too late for the breeding season, Shivkar worried. “Once they get to their breeding grounds, they have to first establish their territory and then woo females. But they may not have time for it. Perhaps they will come back without new offspring this time around,” he said.
Kasambe believes the delayed monsoon and unusual wind patterns may have played a role in postponing migration, but said the reasons remain unclear.
“It is difficult to say why these birds have stayed back for so long. Climatic variations, including delayed monsoon conditions and changes in wind systems that aid migration, may be factors. What we need is long-term data on migration patterns to understand whether climate change is influencing these movements,” he said.
Shivkar, who has been observing the birds for over 20 years, said, “The monsoon winds – a tailwind – helps these birds on their long journeys home, and its delay might be one factor in their overstay. But it needs more studying and more monitoring.”
If the extended stay of the waders occures repeatedly over the years and becomes a pattern, Shivkar worried it may affect their population numbers in the long run. “Migratory birds are a great indicatory series. Their schedule going awry might signal a shift in the balance, and a prenomination of climate change,” he said.
With the beginning of the unrelenting monsoon on Tuesday, both him and Kasambe expect the wader birds to depart.
Ramesh Shenai, India coordinator for Bird Count India, urged caution before treating the sightings as unusual.
“Birding activity during the monsoon has increased only in the last couple of years, particularly after the appearance of several pelagic bird species rarely recorded around Mumbai. We need data collected over many years before concluding whether large numbers of waders this late in the season are an anomaly or part of a regular pattern,” he said.
Shenai said he had also observed significant numbers of mixed wader species at Mamachi Wadi beach in Virar as early as May.
Waders in flight (Photo: Dr Raju Kasambe) 
Lesser Sand Plovers, Curlew Sandpipers, and a Terek Sandpiper forage in shallow wetland waters. (Photo: Dr Raju Kasambe)
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