We owe our knowledge of bird migration to years of painstaking work by scientists. Since 2001, ornithologists from the Bombay Natural History Society (BNHS) have collaborated with the Chilika Development Authority (CDA) and the Odisha Forest Department to study the birdlife of Chilika. Between 2001 and 2005, 6161 birds of 63 species were fitted with specially numbered rings. A large proportion of the ringed birds were recaptured during subsequent seasons, proving that birds return to the same areas every year if conditions remain favourable. This is known as ‘site fidelity’.
Former bird trappers work closely with BNHS scientists, deploying their traditional skills for research. Knowing where to set traps, and selecting the right method for the species being targeted, is crucial for success. Leg-hold snares work well with waders such as sandpipers and godwits. Near invisible nets work with some other species. Strict protocols are followed while trapping, handling, ringing and releasing birds to ensure that they are not harmed in any way.
Once a bird is caught, it is measured, weighed and thoroughly examined. It is then ringed, and released in the same area where it was caught. Each ring not only carries a unique number, it is also engraved with the name of the ringing institution. So when the same bird is trapped by scientists in another location, perhaps even in a different country or continent, it is easy to determine when and where it was ringed, and how far the bird has travelled.
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Bird ringing is a low-tech but highly effective way of studying bird migration. Since 2001, scientists from the Bombay Natural History Society have been ringing winter migrants at Chilika Lake in Odisha.