Monday, 24 July 2006

Birdwatchers highlight partridge decline

Norfolk is partridge country, the one English county where the grey partridge retains something of a stronghold. Yet, even here, it is under threat and populations have continued to decline. New figures, just published for the Breeding Bird Survey, highlight a 40% decline since 1994 and an 87% decline since 1978. The species is now found on just 9% of the 2,879 sites covered as part of the survey, fewer than for red-legged partridge or pheasant.

The causes of the decline are well known, thanks to the vast amount of research carried out, making this one of the best studied of English birds. The grey partridge favours lowland farmland, using areas of mixed arable and grass leys, with uncultivated margins and hedgerows. Although the hens produce more eggs than any other British bird, typically 12-18, productivity has declined massively since the 1950s because of increasing pesticide use and decreasing amounts of predator control. In particular, the use of herbicides has reduced the availability of those invertebrates taken by partridge chicks after leaving the nest. By understanding what has driven the population decline it has been possible to develop prescriptions to manage farmland in a manner which favours the grey partridges. However, such prescriptions have only really been employed on traditional shooting estates, such as Holkham (which, incidentally, boasts the title of Britain’s premier partridge estate), with the wider countryside far from suitable. If we are to halt the decline in partridge numbers then we need to re-establish the network of hedgerows and field margins that are so important for this species.

That we are able to chart the changing fortunes of this and many other species, is down to the efforts and hard work of the thousands of birdwatchers who give up some of their time each year to participate in long-term surveys. One of the most important of these is the Breeding Bird Survey, administered centrally by the British Trust for Ornithology (BTO) and organised by voluntary regional organisers. Although the survey only began in 1994, the data collected can be compared directly with a previous BTO survey – the Common Birds Census – thanks to a period of overlap between the two, which allowed calibration of the two sets of information. Collectively, the surveys provide a long-term dataset, which can be used to monitor the changing populations of many bird species over a forty year period and across a wide range of habitats, something that is unique within the United Kingdom. For the grey partridge, the efforts of those birdwatchers participating in the Breeding Bird Survey provide a means by which we can evaluate the effectiveness of the conservation measures that are being put into action.

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