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Bird decline |
Bird decline
The declines in some songbird populations are a worrying phenomenon. Some of these declines have taken place on a national scale over several decades, but because they happen slowly and gradually, may not be obvious. The national monitoring schemes of British breeding birds are designed to detect any changes in bird numbers, long-term or year to year. Because the breeding success and the winter survival of birds varies from one year to the next, several years of data is needed before it is possible to separate any long term decline from the year to year fluctuations. In any one locality it can be possible to detect changes if bird numbers are compared from one year to the next, or better still, a few years apart. These changes may be linked to national declines, but many of them simply reflect local changes in habitat or the annual cycles of bird behaviour. 'In any one locality it can be possible to detect changes if bird numbers are compared from one year to the next, or better still, a few years apart' A wide variety of reasons can cause real or apparent local reductions in bird numbers any time of the year. These include: clearance of an area of scrub/woodland etc for a housing or road development, grubbing up of hedgerows, and change in the crops planted in surrounding farmland. In towns, even changes in air pollution levels, prevailing gardening fashions and introduction of cats can have a noticeable local impact under some circumstances. These local changes in bird numbers tend to show up rather faster than any underlying national trends, especially if caused by the destruction of the habitat a particular species depends on in the area. For instance, cutting down the only woodland could cause a sudden disappearance of woodpeckers from the area. Seasonal changes in birds’ behaviour can seem equally sudden and dramatic. People understandably get worried when it seems that birds have gradually or suddenly disappeared from their area. In these pages we describe and explain many of the real and apparent reasons why birds ‘disappear’. Last modified: 08 August 2005 |
Flower borders in front of RSPB The Lodge reserve, Bedfordshire - Andy Hay (rspb-images.com, Ref: 1999_0503_009 )
Family Birdwatching through living room window - Andy Hay (rspb-images.com)
Nestbox on tree, RSPB Wood of Cree reserve - Andy Hay (rspb-images.com, Ref: D_2006_11968_0009 )