Why Did Flamingos Flock to Mumbai in Record Numbers This Winter?

More than three times the usual number of migrating pink birds came, possibly attracted by algae blooms caused by sewage

There's a lot more pink in the water during the annual flamingo migration to Mumbai this winter. Photo by Praful Gangurde/Hindustan Times via Getty Images

Since the 1980s, a large flock of migratory flamingos has come to Mumbai with the intent to nom. Between 30,000 and 40,000 of the large pink birds have frequented the capital city of the Indian state of Maharashtra. This year, however, the population of flamingos has tripled, reports Payal Mohta at The Guardian, with conservationists estimating that 120,000 of the birds are hanging out along the mudflats of Thane Creek this year to enjoy a buffet of blue-green algae.

So why have so many extra flamingos joined the party? Researchers suspect one factor may have to do with sewage. Clara Lewis at The Times of India reports that despite the establishment of the Thane Creek Flamingo Sanctuary in recent years, the area has become a hot spot for pollution. A 2016 report on the water quality revealed alarming levels of pollution in Thane Creek brought on by unchecked sewage discharges and illegal dumping.

It’s believed that all of that organic waste is causing a boom in the growth of the blue-green algae in the mudflats where the flamingos go to feast.

“It is a well-studied phenomenon in nature that one species’ waste is food for the other,” Debi Goenka, honorary secretary of the Bombay Natural History Society (BNHS), tells Mohta of the Guardian. “The sewage in the creek promotes biological growth of blue-green algae, which is food for the flamingo.”

Conservationist and naturalist Sunjoy Monga, who has authored a book on Mumbai’s birds, agrees, saying that it’s unlikely there would be so many birds if the human imprint on the body of water wasn’t so apparent. “This phenomenon is called edge nature,” he says. “Here, wilderness merges with human impact and some species are able to thrive in it. It’s a double-edged sword.”

If the spike in flamingos indicates a trend, though, conservationists fear it may be a short-lived one. The mudflats where the birds congregate are under multiple threats: While the sewage and construction debris being flushed down Thane Creek may be the cause of the expansion of the mudflats and adjacent mangroves, without intervention, the sediment build up threatens to block the creek entirely.“Over time, the deposition of sediment has narrowed the channel,” a 2017 study noted. In that scenario, the whole area could dry up, destroying the mangroves and flamingo habitat.

Development is also a concern. Mohta reports that the Uran wetlands, once home to a flock of flamingos, was recently reclaimed for construction of an airport, and the construction of a sea bridge across the Thane Creek mudflats called the Mumbai Trans-Harbour Link caused the birds to move from their preferred location. Last month, authorities also authorized the construction of a bullet train route that would bisect the flamingo sanctuary.

The BNHS is still looking to give a more definitive answer as to why so many flamingos flocked to Mumbai this year. Since launching a 10-year project to study the birds last October, Lewis of Times of India reports that a 20-person team has been responsible for counting the flamingos and testing the water for heavy metals and other pollutants.

Rahul Khot, assistant director of BNHS and principal investigator of the team, says the researchers have already collected some interesting data: Of the two species of flamingos found in Mumbai—the greater flamingo and lesser flamingo—the number of greater flamingos has decreased since October, while the number of lesser flamingos has skyrocketed. In the future, they plan to add radio trackers to birds to gain a better understanding of their migration patterns.

“It’s really good to see large number of birds visiting this metrocity,” Khot says in an interview with NPR, “but that also adds to our responsibility to conserve their habitat so that incoming future coming generation will also enjoy this bird.”

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