Dr Martin Gilbert’s presentation at the Raman Research Institute the other day brought home the drama of understanding bird migration right to our doorstep. For birdwatchers in Bangalore, it would always be that this bird arrived now or departs then. Never had we collectively experienced a thrill of knowing that the particular individual bird seen or photographed came from a particular far off place. This is what exactly happened with us learning that the Bar-headed Geese that our photographers recorded were from far-away Mongolia. And the man who tagged those birds physically there was here with us, to share that experience.
For a very long time, our understanding of the endurance of birds during migration was largely through observations and a process of what is called ringing. A small ring bearing a number and address would be slipped on a birds foot. When this ring was recovered or the bird captured elsewhere, we would now about the movement and timing. The locations of the different sites and the dates of ringing and recovery would give and indication of the speed and distance of migration. In India, this work was largely done by the Bombay Natural History Society.
All this changed with newer technology. The process of putting a small transmitter, (technically called a platform terminal transmitter) whose signals would be received directly by orbiting satellites and relayed back to receiving stations, started throwing up information in real time. It was quite revealing.
For a long time, we thought that birds could fly just a few thousand kilometres non-stop. But we were awakened rather rudely in 2007 when we discovered that birds were capable of flying much greater distances without landing or feeding. A team from the USGS Alaska Science Centre, satellite tracked nine godwits in New Zealand and fifteen godwits in Australia to determine the routes and timing of their migration. These Bar-tailed Godwits are fast flying shore-birds which wade into shallows and feed on invertebrates there, and are just about the size of our crows. What we learnt from the study was truly astounding.
The birds migrated from New-Zealand towards Eastern China, thence towards Alaska, where they spent the summer. They then flew back to New Zealand via Hawaii and other Polynesian islands after their breeding, thus literally ringing half the Pacific Ocean with their migration route. The longest non-stop distance one of the females had covered was over eleven and a half thousand kilometres in just over eight days of continuous flying!
This kind of flying is what even aircraft today do not do. The energy requirement would be high, they would have to combat extreme sleep deprivation and dehydration. These birds are able to put on a lot of fat before migration, which they burn up by the time they reach their destination. This physiological adaptation is only a part of the story.
Discovering all the routes and feats would not have been possible had we just used traditional methods to study migration. Satellite tracking enables recording routes and timing over extremely great distances accurately and helps in determining stop overs too. Satellite tracking of Bar-headed Geese coming to Bharathpur near Agra, has shown that the ‘hop’ to China, just happens within in a day right over the Himalaya, at elevations exceeding twenty thousand feet!
A via media between ringing and satellite tracking, for large birds like Bar-headed Geese, would be the bold neck bands with very ‘visible’ numbers that Dr Gilbert used. Our local photographers have done a remarkable job in photographing such marked geese in our lake-tanks. By this information, the photographed birds were traced back to the place where they were marked in Mongolia in 2008 and 2009. Other birds bearing bands like Great Knots have also been photographed in India.
An important thing we have learnt in many of these studies is that birds also require areas called ‘staging grounds’ where they rest and put on weight before migration. This in a way ties them down to the land. They are thus ruled by the state of the habitat they are part of and become vulnerable to human activities which destroy their habitat. Sadly, two-thirds of the endangered bird species globally are threatened because of habitat loss, and not all of them are migratory.
The local scenario for example, too has been the same story. Birdwatchers in Bangalore used to count the number of water birds found in our lakes every January for a decade ending 1996. Nearly a lakh birds would be counted in about eighty to a hundred sites. Sadly much of these sites are gone and just about a third are perhaps remaining. The birds which wade into the shoreline, the shore-birds, are vastly reduced and hardly a couple of individuals figuratively, are to be seen in those sites today, while they used to occur in the hundreds and thousands earlier. The singular loss of a sloping shoreline in our lake-tanks would have mainly led to this decline locally.
Though water and shore birds normally steal the show when we think of migration, there are others which actually live in our midst. Blyth’s Reed-Warblers and Greenish Leaf-Warblers live on the shrubs and trees that we have here, and could be found right in your garden in Bangalore. These birds too have shown an amazing decline in numbers, with the rampant loss of greenery in Bangalore. Maybe, we all need to think how much land we waste without using optimally, and do something about it. A wanton loss in not even prudent at the least!
Krishna.mb, Wednesday, February 17, 2010.
Published in Deccan Herald.
