Finding out more
In the last hundred years, we have learned much more about bird migration.
All about ringing
By ringing birds, scientists first discovered where they went. Modern technology, such as satellite tracking and DNA testing, has brought us even more detailed information.
Ringing is only carried out by qualified people so that the birds are not harmed or distressed. First, bird ringers catch the bird at a special trapping place, or at the nest when the bird is still a fledgling.
The ring is fitted, details of the species, its age and its condition and the location it is being ringed in are noted and then the bird is released as soon as possible.
Bird rings are designed by the BTO (British Trust for Ornithology), and are made of lightweight metal that does not harm the bird. They come in different sizes to fit different species.
A unique number on each ring shows where and when the bird was caught, and a return address shows where to send information. If the bird is caught or seen somewhere else, this number tells scientists where it has come from.
Only specially trained ornithologists (bird scientists), called ringers, have a licence to do the ringing. The coloured rings on cage birds and racing pigeons are for identifying their owners, and have nothing to do with studying migration.
Catch the birdie
Ringers usually work at bird observatories and other special ringing sites. These are often on islands or headlands where lots of migrants pass through. They use nets with a very fine mesh, called mist nets, which they set up between bushes to catch birds flying past.
Another kind of trap, called the Heligoland trap, directs birds down a narrowing tunnel of nets until they are caught at the end. Large nets are sometimes fired with rockets to catch larger birds, such as geese, as they feed on the ground.
Handling, ringing and releasing birds is a tricky job. Ringers need skill and experience to make sure that birds are not harmed or distressed. First they untangle the bird very carefully. Then they identify it and fit the ring. Finally, before releasing it, they make measurements and record information about its size, weight and age.
Other ways to track birds
Ringing is not the only way to mark birds. Scientists sometimes use brightly-coloured dye on larger birds, such as geese. The colour stands out from a distance so, unlike ringing, there is no need to catch the bird again to check where it has come from. The dye does not harm the birds, but the colour usually disappears when they moult their feathers.
Migrating birds also show up on radar. During World War Two, British forces looking for enemy aircraft noticed unexplained patterns on their radar screens, which they called ‘angels’. These turned out to be flocks of small birds crossing the English Channel. Today radar can even detect individual birds. It can even work out, from the pattern of wing beats, roughly what size they are.
Scientists can now follow migrating birds by attaching lightweight electronic transmitters to them and tracing the signals. At first they used radio transmitters, but these stopped working when the batteries ran out. Today they use solar-powered satellite transmitters, which last much longer.
The signals are beamed back to scientists via satellites in space, and allow them to track every twist and turn of a bird’s journey. A signal was once even picked up from a dead brent goose hanging in the freezer of the hunter who had shot it!
Using your eyes
Don't worry; you don't need satellite technology to observe migration. You can see it with your own eyes. Pick the right time and place, and you'll find that migrating birds are very obvious.
At migration 'hotspots' such as Gibraltar, where thousands of birds of prey pass through every spring and autumn, observers record every one by sight.
And you can do it anywhere: in London, from 24 September to 13 November 1960, a team of observers got up early every morning and recorded more than 4 million migrants. Even oil rig workers have made some amazing observations, recording species such as quails and long-eared owls in the middle of the North Sea!
Observatories are special watch points set up at good migration spots where researchers can observe migrating birds. Most famous observatories in the UK are built on headlands and islands, such as Fair Isle, Dungeness and Portland Bill. Ornithologists who work at observatories also ring and study the birds that pass through.
Moon watching’ is a traditional way of observing migration at night. The idea is to watch the moon during good migration conditions (a calm, clear night during spring or autumn) and to count the number of birds that you see flying across its face.
You won’t spot many, and it is hard to tell what they are. But the number gives a rough picture of the amount of migration from one night to the next. At night you can also listen out for the contact calls of flocks migrating overhead, such as the seep seep of redwings.