Much has been discovered about birds by watching and counting them, but such methods rarely allow birds to be identified as individuals. This is essential if we are to learn about how long they live and when and where they move, questions that are vital for bird conservation. Placing a lightweight, uniquely numbered, metal ring around a bird’s leg provides a reliable and harmless method of identifying birds as individuals. Each ring also has an address so that anyone finding a ringed bird can help by reporting where and when it was found and what happened to it. Some ringing projects also use colour rings to allow individual birds to be identified without being caught.

Although we have been ringing birds in Britain and Ireland for nearly 100 years, we are still discovering new facts about migration routes and wintering areas. However, the main focus of the Ringing Scheme today is monitoring bird populations. Ringing allows us to study how many young birds leave the nest and survive to become adults, as well as how many adults survive the stresses of breeding, migration and severe weather. Changes in survival rates and other aspects of birds’ biology help us to understand the causes of population declines. Such information is so important for conservation that the BTO runs two special projects to collect it. The Constant Effort Sites (CES) scheme provides information on population size, breeding success and survival of bird species living in scrub and wetland habitats. Ringers work at over 130 CES scheme sites each year. The Retrapping Adults for Survival (RAS) project gathers survival data for a wide range of species, particularly those of current conservation concern.

Ringing allowed us to show that declines in the number of Sedge Warblers breeding in Britain and Ireland was linked to lower levels of rainfall in their African wintering quarters. We have also found that the recent dramatic decline in the numbers of Song Thrushes has been caused by a reduction in the survival rate of young birds. This information will help us to identify the environmental factors responsible for the decline.