Insectivores birds such as swifts and swallows, also fly during the day, feeding on insects as they fly; as do flocking birds such as waterfowl and some finches. Most songbirds, however, travel at night. The cooler night temperatures also keeps their body temperature down, allowing them to continue flying while burning less fat than they would during the daytime.
PREPARATION
Birds prepare for migration in many ways. Some hoard the fat in the body. Besides laying down fat reserves, migratory birds also need to eat a lot to keep their feathers in the best condition possible during the flight. For this they need to shed the old worn out feathers and replace them with new ones. This is called moulting.
The ruby-throated hummingbird weighs only 4.8 grams and can use stored fat to fuel a non-stop, 24-hour flight across a 600-mile stretch of open water from the US Gulf coast to the Yucatan Peninsula of Mexico!
NAVIGATION
Birds don’t go to school nor do they learn to use a compass like us; but they find their way with unerring skill! They can reach their destination using the position of the sun during the day, and the stars at night.
Birds can also sense the magnetic north; they have tiny grains of a mineral called magnetite just above their nostrils. Scientists believe these may help them to navigate using the Earth’s magnetic field.
They can identify a location by sight, the smell of the sea, sound of the waves on shores, the winds through mountain passes.
Most amazingly, the location, route and perhaps even the techniques are hard-wired into their brains. Many migrating birds abandon their young as soon as they can fly, and a short time later, the young migrate on their own.
STOPOVERS
Like us, even birds need to stop and refuel themselves during their journey. These are called stopover habitats which are essential for successful bird migrations. Patches of woods, wetlands, mudflats, and beaches with adequate food and shelter are excellent stopovers.
THREATS
Human activities have threatened many migratory bird species, especially since they often cross the political boundaries of countries.Hunting them along the migratory route take a heavy toll. The populations of Siberian Cranes that migrated to India declined due to hunting along the route, particularly in Afghanistan and Central Asia. Power lines, wind farms and offshore oilrigs and changes in the landscape especially reclaiming wetlands as well as a change in the climate all pose a threat to bird migration.
FEATHER FACTS
Bar-tailed Godwits take a non-stop flight of 11,000 km from Alaska to New Zealand. To prepare themselves for this long journey, they store fat in their body. Of their total body weight,55 per cent of it is fat.
Flamingos usually fly by night and travel up to 500-600 kms. They prefer to fly in a cloudless sky when winds are favourable. They fly very high to avoid predators like vultures and eagles.
The longest migration is undertaken by the Arctic Tern. It breeds in the Arctic North in the summer, then flies all the way to to winter on the Antarctic ice pack. The shortest distance between the two poles is 15,000 kms, but the birds travel a longer route, covering up to 20,000 kms and making a round trip of 30-40,000 kms!
