World Migratory Bird Day: Return rate of tagged birds highest in Mumbai: BNHS

More tagged or ringed migratory birds return to roosting and feeding sites in Mumbai and Navi Mumbai than any other region in India.

Lesser Sand Plover was resighted by bird enthusiast Vedant Kasambe on 11 May 2019 at TS Chanakya, Navi Mumbai(Vedant Kasambe)

Bird ringing is done by clipping a bird with a small metal ring to study and understand the routes they use to fly, their migration patterns and resting sites.

Of 10,803 individuals of migratory shore-birds across 46 species ringed in the Mumbai region between 2014 and 2020 (majorly from 2018 onwards) with a recapture rate - recording a ringed bird from the same spot where it was tagged - of 4.6% (497 birds), according to Maharashtra’s nodal agency for bird ringing studies, the Bombay Natural History Society that released data ahead of the 15th World Migratory Bird Day on Saturday. The high rate of birds flocking back show that inter-tidal mudflats in the Mumbai region provide essential feeding grounds for thousands of migratory birds and need to be protected, said researchers.

“The recapture rate is significantly higher than otherwise recorded for bird ringing studies in India. The high recapture data is attributed to very high site fidelity for these migratory birds and intensive efforts of bird ringing over a long period,” said Deepak Apte, director, BNHS.

More recent data from November 2019 to January 2020 showed 3,453 birds ringed by BNHS across wetlands near Bhandup pumping station in Mumbai, the Thane creek and TS Chanakya wetlands in Navi Mumbai. Of these, 3,415 were small waders and 38 flamingos with 160 recaptures during the exercise. Most of these winged visitors descend to Mumbai after spending the summer in Arctic Russia, said BNHS.

“This kind of data repository is not available along the west coast for any location so far, including the Gujarat, Goa, Karnataka and Kerala coast, which witnesses the highest bird numbers,” said Apte.

According to BNHS, a shore-bird ringed on the west coast of India carries a metal ring in one leg and two-coloured flags (one with alphanumeric engraving and another blank) in the other leg. The position of ring and flag also changes according to the year they are tagged. The left leg carries the metal ring during the odd year and right leg carries coloured flags and vice-versa for even year.

BNHS also collated 376 resighting records (tagged birds spotted rather than checked for details like alphanumeric engraving) from birders and wildlife photographers. “Mark-recapture studies with migratory shorebirds have always proven to give low recapture rate and hence resighting records are also considered as recapture,” said Rahul Khot, assistant director, BNHS. “Interestingly, 80% of the recaptures recorded by us were from the sites where the birds were tagged. For example, a bird ringed in 2014 at Panje wetland in Uran was recaptured in 2018 in Panje even after four years.”

Apart from the Lesser and Greater flamingos, birds ringed by BNHS include a large number of waders such as Little Stint, Curlew sandpiper, Lesser Sandplover, Common Redshank, and Black-tailed Godwit whereas rare species included Red-necked Phalarope, Spotted Redshank, and Bar-tailed Godwit.

Independent experts concurred with BNHS’ findings. “The global recapture rate is around 2-3%, and this indicates that these Mumbai wetlands need to be conserved. However, we must try to understand how the migratory birds use these mudflats, whether they are becoming their winter homes permanently or these are stopover points for their final destination,” said Dr Asad Rahmani, member, Wetlands International South Asia and former director, BNHS.

Sunjoy Monga, ornithologist said, “The findings are accurate. A sizeable ringed population of birds frequenting key wetland sites annually makes it a clear case for protection of these wetlands.”

World Migratory Bird Day

In 2006, the United Nations decided to celebrate the second weekend of May every year as World Migratory Bird Day in order to raise awareness about the migratory birds and their linkages between different regions across the globe. Every year a unique theme is chosen. This year’s theme is ‘Birds connect our World’, which was chosen to highlight the importance of conserving and restoring the ecological connectivity and integrity of ecosystems that support the natural cycles essential for the survival and well-being of migratory birds. During their annual cycle, flyways are used by birds for breeding, stopover, and wintering zones. Globally, nine migratory flyways have been identified under the Convention of Migratory Species (CMS). CAF is one of them covering migratory bird routes across 30 countries with maximum routes passing through India.

SOME INTERESTING FACTS ABOUT THE MIGRATORY BIRDS

The highest flyer: Bar-headed Geese travel every year from their breeding grounds in China and Mongolia to India and while doing so they cross the Himalayas, flying above 29,000 feet. No other bird is able to do so.

The longest non-stop flyer: Bar-tailed Godwits are able to fly non-stop from Alaska to New Zealand during which they cover a staggering 11,000 km within six days. Before embarking on this journey around 55% of their body weight is stored as fats to power this tiring journey.

The all-time record holder: Arctic terns travel from the North Pole to South Pole and back. Studies indicate that on an average they travel up to 70,900 km annually. In their lifetime they would complete the distance equivalent to going to the Moon and back three times.

(Source: Siddhesh Surve, assistant director (capacity building), Maharashtra Mangrove Foundation)