Imagine you hatched out of an egg in a nest near Smithers, you joined your parents on a major flight down to Central America or even northern South America to spend the winter. Then, next spring, you returned north and found your way back to the exact place you were born – no maps, cell phone, guides etc. Could you do it? Many birds can and do year after year.
Even more amazing is that some fledgling birds do not migrate south with their parents but manage on their own to find the same wintering grounds that their parents go to. The ability to go to the same place each time is called site fidelity or philopatry.
Bird migration is a puzzle that scientists have been trying to figure out for a very long time.
We do know that many bird species make long-distance northward migrations in the spring to breed. Even though the journey can be perilous, it offers a clear advantage. Less competition for the abundant insects, food and breeding habitat in the north means that, on average, the migrants can rear 4-6 offspring per year whereas only 2-3 offspring are reared by the same species remaining in their wintering grounds.
We know that birds use the stars and moon at night and the position of the sun during the day like a compass. They also seem to be able to recognize geographical features and it could be that familiar smells guide them to food stops along the way.
For sure, the birds use the earth’s magnetic field to sense which direction to fly in and some species have small amounts of magnetite in their bills that help with this. What we are not sure about is how they know where they are initially, or at any one point along the way.
Recent research studies suggest that birds use a special form of GPS to know exactly where they are at any point in time. Researchers modified the magnetic field within special cages designed to study migratory instincts. Birds placed in these large cages would attempt to fly in a direction that would place them back at their normal migration starting point.
In other words, the birds were able to figure out that they were not in the correct “map” position to start their migration and could not make the necessary adjustments. Birds in cages where the magnetic field had not been modified tried to fly in their normal migratory direction.
