Why Ring Birds?
Bird ringing is an essential research tool for biologists and conservationists alike and is used around the world to study the lives of birds. Uniquely numbered rings allow us to follow the life and behaviour of individual birds and answer questions like how long does a bird live for? Where do migratory birds go in winter? Finding the answer to such questions can provide us with vital information, enabling us to take appropriate action when their populations become endangered. The answers also provide us with facts that never cease to amaze and enthral us. Who would have believed before the advent of ringing that Swallows breeding in Britain and other parts of Europe fly some 8000km, crossing seas and deserts, to winter in South Africa.
With so many bird populations in decline throughout the world, it is becoming increasingly important that we can monitor the health of populations. Whilst surveys that record birds by sight or sound can provide useful information, monitoring birds using ringing studies can provide considerably more. Not only can the ringing of birds tell us whether a population is declining or increasing, it can tell us which members of a population are responsible for such changes, as the age of ringed birds is known. For example, population declines may result from either increased mortality of adult or juvenile birds, or may be due to a decrease in the number of chicks surviving to independence.
The Song Thrush has declined significantly in Britain and is now on the red list of Birds of Conservation Concern. Analysis of ringing data by the BTO has shown that dry summers can cause a considerable reduction in the breeding success of this species. This seems to be linked to the birds finding it more difficult to capture prey such as worms when the ground is baked hard.
The migration of billions of birds every year is one of the most remarkable of natural events. In Europe alone, estimates suggest that 4 billion individuals belonging to 200 species make the journey to their African wintering grounds every autumn. Whilst a visit to Africa during the Northern Hemisphere winter will reveal the presence of many of these migratory species, it is impossible to tell where in Europe these birds originated from. The ringing of birds has been instrumental in increasing our understanding of these movements, not only allowing us to discover where they go in Africa but also where they stop along the way. Sometimes the strategies birds adopt and the routes they take are quite surprising. Sedge Warblers ringed in North-west Europe, for example, were regularly recorded on the Atlantic coast of France but rarely further south in Spain or Portugal. It became evident that unlike many migratory species, which stop around the shores of the Mediterranean before attempting to cross the Sahara, Sedge Warblers appeared to routinely make a non-stop flight from France all the way to sub-Saharan Africa. For a bird that typically weighs less than 11g, this flight of 3000km is a phenomenal undertaking. Other species of migrants take completely different routes depending on which part of Europe they originate from. It is not uncommon for individuals that breed in Western Europe to migrate south-west through Europe to wintering sites in West Africa whilst individuals from Eastern Europe migrate south-east, passing through Egypt and the Middle East to wintering areas in East Africa.
These maps show where Swallows and Sedge Warblers that were fitted with uniquely numbered rings at the Wetland Trust's reserve in Sussex, England were later caught. Those caught within Britain will have travelled to Africa and back at least once before being caught close to their breeding areas.