Bird migration is a rather mysterious occurrence and if you have never thought about it you should! Birds migrate during the day as well as at night and cover enormous distances to travel to warmer climates during the cold winter. So how do birds travel and know the exact location of where they are heading without an obvious GPS device? First, a lot of song bird species (warblers, thrushes) migrate at night, setting out shortly after sunset due to calmer night climates and also in order to avoid predators that might catch them during the day. The nights are also cooler so the birds don’t over-heat. Birds like Swainson’s thrushes actually send out strong vocal signals to let other birds know where they are heading. The path songbirds take during their migrations are usually quite broad. Often they will move between their breeding grounds and the path often depends on the winds. Since these bird species are small they get blown around a fair bit so they wait for the ideal wind direction before they take flight. Another amazing fact is that around the time birds migrate many of the birds are only a few weeks old, conseqently many don’t make it past a year due to the rigours of migration.
So how do these young birds know where they are going? The birds use the direction of the sunset to cue them, they know which stars are at the centre of rotation (look for the North Star) and even have a magnetic compass all guiding them to their destination. There are thought to be about 9,700 bird species that migrate around the world. But this is not a perfect system. Unfor-tunately we, humans produce such great amounts of light pollution that birds can sometimes lose their way. The tall communication towers are the worst culprits, causing the birds to fly towards the red light and crash into unlit guidelines by the towers. But for the most part, birds have survived thousands of years of changing climates and terrains and managed to continue to ha-ve almost perfect insight when it comes to finding their way.
The writer is a Ph.D. in Molecular Genetics and Genomics and is working on skin cancer at Novartis