Return of Bala, the black-tailed godwit, from Siberia

For scientists at the Bombay Natural History Society (BNHS), it was a ‘Eureka moment’ when they spotted ‘Bala’, the black-tailed godwit (BTG), Limosa limosa at its home base, the Thane Creek, where it had returned after its summer sojourn in Siberia.

Named after Dr S Balachandran, the eminent ornithologist who has played a key role in the ringing and tagging of nearly three lakh birds, Bala had been fitted with a GPS tag in March this year. Covering a distance of 5,000 km in 47 days since April 24, the bird reached the breeding site(s) in southwestern Siberia, Russia, on June 11. In its northward migration, the bird used several staging and stopover sites crossing six countries: Pakistan, Afghanistan, Turkmenistan, Uzbekistan, Kazakhstan and Tajikistan. The southward migration back to Thane Creek, however, was very quick and Bala took just five days from July 17 to cover 4,200 km. “These birds fly at a high elevation, which gives them a good speed,” says Dr Khot, project head of the experiment. The tracking device tagged to this medium-sized wader helped to identify the bird when it came within the range of its home base.

While details of the findings will be released over the next few months, scientists are already excited with the preliminary findings. “The rate of re-sighting a bird is hardly 2-3 per cent, and it can sometimes take even 10-20 years to re-sight a tagged bird,” says Dr Khot. The data collected from the GPS tag, he adds, will be crucial for understanding the migratory behaviour.

“The tag will help us understand flight basics like the height at which the bird was flying, the speed of flight at different intervals, besides the conditions and areas preferred for flying and stopover, etc. The data will be useful for the conservation of wetlands where biodiversity flourishes,” says Dr Khot, adding that over the next few years more GPS tags will be deployed.

The bird, usually 40-44 cm in length and weighing 280-340 gm, can be recognised by a strikingly long, slightly uptilted bill with a pale (usually pink) base, dark tip and a black tail. The global population of this species has been declining, and they are categorised as a near-threatened species. While the species is relatively well studied in the East-Asian Australasian flyway and African-Eurasian flyways, little is known about their population status, migration trends and ecology in the Central Asian flyway, which is the flyway that this godwit took.

On why it is important to understand the migratory route, Dr Balachandran says, “Migratory birds play a major role in balancing the ecosystem. It is essential to understand their route to conserve the species. Knowledge about their traditional stopover and breeding sites, besides the number of days they stay there, can help in the formulation of policies that do not disturb their places of stay.”

“Interestingly, while it is essential that the specific areas near their habitats and breeding areas should not be disturbed or have human activity nearby, the presence of a large number of migratory birds at Thane Creek, which is surrounded by three major metropolitan areas of Thane, Mumbai and Navi Mumbai, continues to baffle scientists,” says Dr Khot.

While the satellite tracking studies of birds had started at BNHS eight years back to understand if birds migrating from China were carriers of bird flu (H1N1 virus) to the poultry farms in India, which is their major winter migrating area, the GPS transmitters/GSM tagging of many migratory birds was undertaken this year to understand their migratory route.

Dr Khot says many factors have to be taken care of when tagging. “The bird should be healthy and have adequate body mass to be able to carry the tag, which should not weigh more than 2 per cent of its body weight. It must be put very cautiously, else it can even cause a physical shock.” Fitting a GPS tag and then subsequent clearances and expenses can take the cost of radio tags to around Rs 1.5-3 lakh — smaller the tag size, higher is its cost. Tagging, however, is just a small part of the story, and to retrieve data a bird must survive, GPS tag should be intact, and it must come within range of a receiver.