Blackbirds feeding on insects and on the berries on shrubs and plants in gardens are a familiar sight in autumn and winter. While many householders might think they are the same blackbirds, it is not always the case, as blackbirds are migratory birds and can travel over mainland Europe and as far north as Scandinavia.

So how does anyone tell them apart?

This is where the ringing of birds comes in to help find out how and when birds move around the countryside and from country to country — though is is not something the casaul birdwatcher from the kitchen window will want to undertake.

A small group of members have resurrected the bird ringing once carried out by Banbury Ornithological Society (BOS).

They spend a fair amount of their spare time ringing birds and recording them and passing on their results to the British Trust for Ornithology (BTO).

The BTO co-ordinates all the records sent into them from a large network of bird ringers and it is able to draw up maps that enable it to discover how the migratory flights of birds change over the years and how species are thriving or whether they are endangered.

In fact, the work of bird ringers complements the other methods of counting birds undertaken by societies like the BOS and people taking part in the regular Big Garden Watches run by the Royal Society for the Proection of Birds (RSPB).

One of the ringers in north Oxfordshire is Andy Turner, who has been a member of BOS for about ten years and who has been ringing birds for about two years.

“Ornithologists have been ringing and recording birds in Britain for 100 years this year.

“We have to be licensed by the Department for the Environment and Rural Affairs through the BTO.

“It takes several years before you can go out and ring birds on your own,” said Andy, who lives in a village near Banbury.

There are three levels of licence beginning with trainee status and working up to being fully competent and able to work alone.

A trainee always has to go out with a fully-fledged trained ringer to learn how to handle birds.

“The safety of birds being captured and ringed is paramount. The trainee has to learn how to take out a bird from the net in which it has been captured and how to put a ring on a bird’s leg without causing distress or injury,” said Andy.

Birds are caught by using very fine nets known as “mist nets” that are strung between poles against something like a hedge so the birds cannot see the net in advance.

Rings are of different sizes and weights depending on the size of the bird.

For example, birds such as sparrows or finches are small compared with gulls — at least eight gulls are found in Britain.

All rings are identified by codes that are unique to the ringer and registered with the BTO.

“Some rings have different colours too and in colour combinations such as black figures or letters on an orange background.

“Some rings too are put on right or left legs of a bird,” said Andy.

The colours and leg on which a ring is attached mean that the rings can be read at distance by ornithologists using binoculars.

Andy added: “This enables a birdwatcher to easily record the information and pass it on to the BTO and the ornithologist who put the ring on, as everything is recorded.

“In this way, birds can be tracked around the country, as can their flights to and from mainland Europe. For example, an ornithologist in Germany can tell me that a bird I have ringed has turned up in his patch.”

Gulls are a relevant example of the benefits of ringing. At one time gulls were found mainly in coastal regions but they have moved inland, probably because shoals of fish have moved to another part of the seas, possibly due to changes in water temperature or because of over-fishing.

“Gulls these days, such as the herring gull or the black-headed gull, can be found feeding on rubbish tips where there are often easy pickings. I have recorded gulls at Ardley quarry, near Bicester, and also on tips in Essex.

“However, we are not sure what will happen to the population of gulls — some of which are endangered species — when landfill sites are closed in the coming years,” said Andy.

Apart from discovering the movements of birds through ringing, a bird ringer can tell the health of a bird.

“You can tell how well a bird is from the size of the pectoral muscles and also the length of wings. You can also find out from its condition whether a bird has been struggling against bad weather on a flight into this country from Europe.

“All information that can be gathered is important in assessing what is happening to birds as so many birds that were once familiar are now endangered,” said Andy.