Like an aeroplane that tanks up before international flight, migratory birds fatten themselves up, some to the point of doubling their weight, by bingeing on energy foods ahead of their intercontinental flight, says a study.
The findings, which were part of a study by German scientists and researchers of the Gurukul Kangri University in Haridwar, were revealed at a workshop organised by the university in the city on Saturday.
The dean of department of zoology and life science in the university, Dinesh Bhatt, said: "The migratory birds feed on food which gives them energy before taking flight. They fly nonstop for thousands of miles.”
Migration is the seasonal movement of birds, sometimes in search of food and sometimes to breed and raise their young. These migratory birds include both aquatic and forest varieties.
Some migrants almost double their body weight by storing fat before migration, said Frenze Vierlin, the director of Institute of Avian Research in Germany, who was part of the study.
"To prepare for migration, birds become hyperphagic - meaning they eat more food, which is stored as fat for their long migratory journey. Fat is normally 3% to 5% of a bird's body mass. Some migrants almost double their body weight by storing fat before migration," he said during his visit to Haridwar.
So how do birds know it’s time to gorge on fat-rich food.
Their body is programmed to release certain enzymes during the migratory season of the year, which sets off the urge to pick up fat-rich diet, said Bhatt.
Through the central route of the globe, 322 species of birds migrate to India from Europe while 281 come from the African subcontinent.
Arctic tern, a seabird, holds the record for longest migration distance—flying about 30,000 km each year travelling between its Arctic breeding ground and non-breeding area in the Antarctic.
Only 29% of bird species migrate from one country to another. Birds such as hawks and vultures migrate during the day while many songbirds are unable to fly to their non-breeding grounds non-stop. They make pit stops to rest and feed during migration.