Amazing Facts About Avian Migration
Most people are aware that some birds migrate but it is only relatively recently that we have become aware of migration. It was only in the 19th century that it became evident that birds might be spending their winters elsewhere. The evidence arrived in the shape of a stork which landed in Germany with an African spear through its body. The ancient Greeks believed that birds turned into fish over the winter!
Indeed different societies across the world had some fantastical explanations for the absence of the birds in the winter months. Some people thought that birds turned into barnacles whilst others believed that the birds were hibernating in cliffs or at the bottom of ponds! Now we know better!
The earliest clues about migration were provided by captive birds in the 18th century. Birds were seen to be behaving strangely at the time of the year when they would have migrated. The caged birds would become restless, more active at night and gain weight. They would also scratch at the same area of the cage repeatedly.
Migration is dangerous and many of the birds who set out for warmer climes never arrive at their detination. Young birds are particularly vulnerable and it is thought that over 80% of songbird deaths are those of young migrating birds. But there is evidence to suggest that the birds which do survive their first migration tend to live longer than those which don’t migrate at all.
How to They Do It?
Birds benefit from an internal clock which tells them when it is time to travel. They sense the time coming and begin to physically prepare for the journey. Birds tend to gain weight prior to migration and some of their organs shrink to enable oxygen and fat to be used efficiently in flight. In many cases the migration route is written into the birds’ genes whilst other species follow relatives on their journeys. Interestingly when scientists crossbred species with different migratory routes, the offspring followed a path halfway between those of their parents!
Finding the Same Branch
Birds are such brilliant navigators that they can return to exactly the same place year after year and we have yet to discover how they do it. They can fly thousands of miles and land on the same branch as the previous year!
Sniffing Out a Route
Birds need their sense of smell in order to migrate. Research into homing pigeons has shown that without their sense of smell, these birds stop being able to find their way back to their home. Recent experiments have demonstrated that migratory birds also rely on their sense of smell.
In adidition, birds can navigate via the Earth’s magnetic field. They can’t tell the difference between north and south but they do know whether they are flying towards one of the poles or the equator. It is thought that birds may be able to tell where they are using the magnetic field but this ability is yet to be fully understood.