Strictly for the birds

Tony Gilland questions the assumption that modern agriculture is threatening farmland birds

Conservation groups claim that modern pesticides have been so effective in removing weeds and insects in farmers' fields that many birds are being starved of their food supply. GM crops, they argue, might usher in yet more effective farming practices and make the situation worse. Data from the British Trust for Ornithology (BTO) shows that tree sparrows have declined by 87 percent, grey partridges by 78 percent, corn buntings by 74 percent and reed buntings, turtle doves, skylarks and yellowhammers all by 60 percent or more during the period 1972 to 1996. These species form part of the Department for the Environment, Transport and the Regions' (DETR's) new index of 20 more common 'farmland species' which have fallen from a base value of 100 in 1970 to a value of 69 in 1997.

As the plight of birds has already played a major role in determining the future of GM crops, it is worth taking a closer look at the assumption that intensified farming has caused their decline.

Attention has focused on correlations made between the decline in a number of species of birds, which began around the mid-1970s, and changes in certain agricultural practices since that time. This work seems to indicate that new agricultural practices have had a negative impact on birds that live predominantly on farmland (specialists), while other species (generalists) have coped with the changes rather well. But conducting the field experiments necessary to prove how specific factors impact on particular birds is difficult and expensive, and there are many hypotheses to be tested. BTO experts acknowledge that they 'remain ignorant of the precise causes of the majority of farmland bird declines' (Baille et al, Farmland Bird Declines: patterns, processes and prospects, 1997). Even on the hypothesis that pesticides reduce available food supplies, many ornithologists accept that 'the only species for which such an effect has been demonstrated beyond doubt is the grey partridge'.

Yet in response to the question 'can we be sure that the bird declines in the United Kingdom are caused by agricultural intensification?', four leading ornithologists recently argued that 'most of the evidence is by association, but in sum total it is damning'. They cited annual BTO censuses for 42 species of breeding birds, which show that 13 species of farmland specialists - such as the skylark and corn bunting - declined by an average of 30 percent between 1968 and 1995. Meanwhile, 29 species of habitat generalists - like the carrion crow and the wren - have increased by an average of 23 percent. Apparently, generalists are more able to adapt to change and to nest and feed elsewhere, while those whose ecological requirements are more specific - and used to be well-suited to farmland - are suffering the consequences of agricultural change (Krebs et al, 'The second silent spring?', Nature, 12 August 1999).

This argument is highly plausible. Birds found on and around farmland are living in a habitat heavily shaped by human activities, so one would expect changes in these activities to have an impact. But these correlations and indexes hide a lot of important contextual information. There are many more bird species to be found on farmland than the so-called specialists. As Krebs et al point out, the 29 generalists found on farmland 'have increased by an average of 23 percent'. So even though 75 percent of UK land is used for farming and the specialists are thought to have declined by around 30 percent, our countryside is certainly not becoming devoid of birdlife.

Despite intensification of farming, not all the specialists are declining. For six of the 20 'farmland species' included in the DETR index (goldfinch, greenfinch, woodpigeon, whitethroat, jackdaw and stock dove), BTO data shows an increase in population, four by more than 50 percent. This suggests that the relationship between intensification and bird populations is not as straightforward as some might have us believe. Dr Dick Potts, director general of the Game Conservancy Trust, is convinced that agricultural changes are the primary cause for the decline of six to eight species, but for others 'the jury is still out'. According to Potts, 'people have been too hasty altogether to blame farming, which in recent years has improved in many ways', while other plausible factors have received less attention. And even if some species have declined as a result of intensified agricultural practices, the real question remains, 'so what?'.

This was the response of Michael Lancaster, a retired scientist who describes himself as an 'amateur ornithologist' and a 'loyal member of the BTO for the past 30 years'. He has become increasingly concerned about the misleading impression being created by the use of panic-laden statistics, and argues that too much emphasis is placed upon the category 'farmland' in relation to birds. The skylark, he points out, is naturally a species of steppe which has taken advantage of farmland while it can. If it is now retreating from a less favourable habitat which it once expanded into, 'so what?'. There are currently thought to be over a million pairs of skylark breeding in Britain despite their decline. And according to the BTO, 'after a severe population decline between the mid-1970s and mid-1980s, the population has remained relatively stable' (Crick et al, Breeding Birds in the Wider Countryside: their conservation status (1972-1996), 1998). So while BTO data might show a striking 60 percent decline from 1972 to 1996, over the past 10-15 years its data presumably shows relatively little change.

Dr Tim Sharrock, managing editor of British Birds and coordinator of the BTO's first Bird Breeding Atlas in the early 1970s, is similarly sanguine. Prompted by mass media coverage of 'the latest doom-and-gloom story', Sharrock wrote an editorial for the September issue of the journal entitled 'Panic ye not', which counselled against looking for 'the one simple answer'. Tim Sharrock and Michael Lancaster seem to share a philosophy that change, whether due to 'natural' effects or man's impact, is to be expected and should be no cause for alarm. As Sharrock explains, 'these birds are only here because of the inefficiencies of past agricultural methods'. He adds that 'as some species decline, others increase and take their place'. Indeed, a recent BTO report found that 'the number of species showing long-term trends of declining population size approximately equalled the number showing increases' (Crick et al, 1998).

Lord Derek Barber is even more critical of the way the current debate about birdlife has been shaped. Lord Barber, who was the chair of the Royal Society for the Protection of Birds (RSPB) from 1976 to 1981, and chair of the Countryside Commission from 1980 to 1990, argues that 'everything as far as the RSPB is concerned is always in grave danger. Bodies like the RSPB and Worldwide Fund for Nature cry wolf at every opportunity. They tend to go for exaggerating all the time and they tend in due course to believe their own exaggeration'.

So what if bird populations are changing? None of the 'farmland species' hitting the headlines as a result of press statements released by conservation organisations is endangered. And while conservationists might point to the government's Biodiversity Action Plans, and its commitment to 'halt or reverse' the declines of many of these species, others might ask why these commitments were made in the first instance.

Corn bunting, grey partridge, tree sparrow and skylark are all birds which have featured in many alarmist press statements, and for which there are Biodiversity Action Plans. Corn buntings breed in their millions in Spain and Turkey and are thought to be currently enjoying a population increase in these preferred locations, where the climate is warmer and drier. Skylarks and tree sparrows breed in their millions around the world, and even the grey partridge, which is less numerous, is not listed as a 'globally threatened' species. More than 1100 of the world's 10 000 identified bird species have been listed as 'globally threatened'. Yet only 24 of these 1100 species breed in Europe, and only a handful in the UK (Globally Threatened Birds In Europe, Council of Europe, 1996). This shows the need for some perspective: why should these birds be of any real concern to the British public and its government?

When everything is taken into account, it seems that this discussion has very little to do with birds. Rather, it has become one more way to raise broader concerns about modern farming, and particularly GM crops. Whatever the problems or potential with new agricultural technologies, getting into a flap about birds will not help move this debate forward.