आभाळातल्या पाऊलवाटा Aabhalatalya Paulvata (Footpaths in the Sky - Bird Migration)

पक्ष्यांच्या दुनियेतली एक आश्चर्यकारक गोष्ट म्हणजे अनेक पक्षी वर्षातून दोनदा हजारो मैलांचा प्रवास करतात. हिवाळ्याच्या सुरुवातीला भारतातील सरोवरे अचानक हजारो बदकांनी भरून जातात, जे काही महिन्यांपूर्वी तिथे नव्हतेच.

The author notes that many things about birds are astonishing, but the most striking is the thousands-of-miles journey that many bird species make twice a year. At the start of winter, any lake in India appears literally covered with different species of ducks - birds that were nowhere to be seen just a month or two earlier. The author poses the question: where do these thousands of birds suddenly come from?

बदकांसह असंख्य पक्षी युरोप व उत्तर आशियातून हजारो मैल प्रवास करून हिवाळ्यात भारतात येतात - श्वेतबलाक जर्मनीतून, तर काही बदके सायबेरियातून येतात. कालिदासाच्या साहित्यातही या स्थलांतराचा उल्लेख सापडतो.

The author explains that not just ducks but countless other bird species regularly arrive in India from Europe and northern Asia at the start of winter, after journeys of thousands of miles. The white storks that visit India come from Germany, while some duck species come from Siberia. References to stork migration appear even in the writings of Kalidasa, and ancient literature notes that swans disappear during the monsoon, though it offers no clue as to where they actually go. In Europe too, birds vanished each winter, but exactly what became of them remained a mystery for a long time - some believed the birds buried themselves in mud like frogs and hibernated. It was only once humans began travelling from one continent to another that people realised birds vanishing from one continent appeared in another during the same season.

पक्ष्यांचे स्थलांतर अभ्यासण्यासाठी शास्त्रज्ञ त्यांच्या पायात हलके ॲल्युमिनियमचे वाळे अडकवतात, ज्यावर संस्थेचे नाव व क्रमांक असतो. हे पक्षी नंतर पुन्हा सोडले जातात, आणि जेव्हा कोणाला असा पक्षी सापडतो तेव्हा तो संस्थेला कळवतो.

Studying bird migration is not easy, but a simple method has been used for the past century - catching several birds in a given area and fitting lightweight aluminium identification rings on their legs, marked with the research institute's name and a serial number. The banded birds are then released, and it is hoped that whoever finds such a bird, alive or dead, will report it to the institute. Not every ring is ever recovered, but even one or two out of a hundred can yield valuable information - for instance, wagtails ringed in Kerala have been found in Kabul, Afghanistan and north-western Pakistan, while a stork ringed in Germany was found in Bikaner. In recent times, aircraft and radar systems have also provided valuable information about migration, though many mysteries of these habits remain unsolved.

हिमालयातील पक्षी थंडीत खाली दरीत उतरतात व उन्हाळ्यात परत वर जातात, हे कमी अंतराचे स्थलांतर आहे. दुष्काळ किंवा बर्फवृष्टीमुळे अन्न न मिळाल्यास पक्षी तात्पुरते दुसरीकडे जातात - अन्नाची कमतरता हीच स्थलांतरामागची मूळ प्रेरणा आहे, थंडी नव्हे.

The author explains that bird migration takes several forms. Birds in mountain ranges like the Himalayas descend into the valleys during winter and climb back up in summer - a relatively short journey. When drought, floods or heavy snow make food scarce in an area, birds temporarily leave for elsewhere; scarcity of food, not cold, is the fundamental driver of migration, the author clarifies. If food is plentiful, birds can thrive even in snowy regions - as shown by the alpine chough, normally found at two to five thousand metres, which has been recorded following Everest climbers up to about 8,500 metres, apparently unaffected by the cold, snow or thinning air at that altitude.

काही पक्षी बर्फ पडण्याआधीच, अन्न पुरेसे असतानाही दक्षिणेकडे प्रवास सुरू करतात. सूर्य दक्षिणेकडे झुकताच त्यांच्या मनात अस्वस्थता वाढते आणि ते ठरावीक मुहूर्तावर उडून जातात - हे जणू त्यांच्या जीवनाचा धार्मिक विधीच बनला आहे.

Finally, the author notes that many birds begin their journey south well before snow starts falling, even while food is still abundant. These birds do not wait for food to run short - as the sun begins to tilt southward, an inner restlessness stirs within them, a pull towards the south grows, and they become agitated. Many birds of one species gather together and set off at a particular moment. For these birds migration is no longer tied to food at all; taking flight in a set direction during a set season has become, almost like a ritual, simply a part of their lives. And with spring's return, the same unnamed pull draws them back north to their homes.