Migration is one of the most studied, yet poorly understood aspects of the natural world. Let us look at the history of man’s observations on migration, on how man first began to notice and explain the appearance and disappearance of birds and animals around him. Young naturalists will discover in time how migration and animal behaviour are closely linked.
As the monsoon wanes and winter arrives, there is a noticeable change in the birdlife over most of the country. Hundreds of thousands of migrant birds from the Himalaya, central Asia and Europe now come into mainland India, scattering over the length and breath of the land, from the Himalayan foothills to the extreme south; from dense jungles and open scrub, to grasslands, coastal stretches and islands. On the move are giant birds such as cranes and storks weighing 15 kg. as well as tiny Willow Warblers weighing barely a few grammes. All may undertake journeys of several thousand kilometres.
Come wintertime, even the most casual observer will notice an increased number of birds, be it in the wilderness, or in the midst of the city garden or even your own backyard. Though most forms of animal life, including reptiles and insects undertake great seasonal journeys, it is the birds, which best typify migration.
It was not until the time of Aristotle, that great naturalist who lived between 384 and 322 B.C., that the first explanations of migration emerged. In his enormous work of natural history, the Historia Animalium, Aristotle suggested that some creatures stay put for winter, while others move to the south after the autumn equinox (about September 22) to avoid the cold. Following the spring equinox (March 20), these species move northwards again, he said, this time to avoid coming heat. Aristotle was also the first person, perhaps, to realise that while certain creatures undergo local migration, others like cranes “may be said to come from the ends of the world.”
Aristotle also wrote “The birds in front wait for those in the rear, owing to the fact that when the flock is passing over the intervening mountain range, the birds in the rear lose sight of their companions.”
This more than 2,000 year old observation could also explain why and how flocks stay together. Yet, another of Aristotle’s classic observations was that “All creatures are fatter in migrating”. This has been confirmed by recent scientific studies. Hormonal changes cause the birds to develop more fat, thereby ensuring energy for their long arduous journey. Further studies have revealed that it is only after the fat content has exceeded a certain critical level that actual migration commences!
Of course, in that early time, Aristotle did make some errors. He said, for instance, that some birds might hibernate instead of migrating for winter. “Some birds decline the trouble of migration and simply hide themselves where they are”, he wrote. Birds that Aristotle must have found in cavities and suchlike shaded confines were most certainly dead, and not hibernating birds (one American bird – the oilbird does indeed hibernate). Amazingly, this view of hibernation remained in vogue for almost 2000 years. Aristotle also put forth another bizarre theory – that of transmutation – saying that some species changed into others with the seasons!
400 years after Aristotle, Pliny, the Roman naturalist (20 to 79 A.D.) wrote about migration but his ideas did not differ much from Aristotle’s. Pliny also said that hibernation and wakening are determined precisely by the stars. For nearly 1,500 years after Pliny, migration seemed to have taken the backseat for advancing mankind.
Emperor Frederick II of Germany (1194 -1250 A.D.), himself a fowler and falconer, came up with some intelligent ideas on migration saying that “not all (birds) do so (migrate) by moving great distances; some come down from the mountains to the valleys as winter approaches and climb again in the spring.” He also said that the exodus might be delayed if food is plentiful and weather is good. He described the V-shaped formation of the high-flying geese and cranes. But some of the beliefs were pure poppy cock!
More than 300 years later, Olaus Magnus, the Archbishop of Uppsala actually swore that the swallows spent the winter under water! Many a great scientist-naturalist in the years to come, including the great Swede, Linnaeus accepted, in some measure, the theory and story of swallow immersion.
And so on, more and more observations were put on migration in the years to come until early scientific investigations began in the nineteenth century.
Things to do
You could begin right away by new bird arrival in your neighbourhood. Make a note of the date and the kind of trees on the ground upon which you see them. Note the weather conditions, temperatures etc. in your diary. This will help you compare their arrival from year to year with the prevailing climatic condition.
For instance, if winter is delayed, perhaps their arrival too may be delayed. Note down how many birds you see together, i.e. singly, in pairs or in flocks. Do they enjoy the water and do they hunt fish?
Very often, resident Indian birds seem to enjoy fish, while some migrants tend to enjoy eating grain and vegetable matter. Only if you can follow them closely, armed with binoculars and patience, will you be able to discover what they eat.
The writer is the editor of Sanctuary Asia magazine