There is a decline in the farmland bird indicator and this is attributed to agricultural intensification. However, we know that other drivers play their role, for example climate change. For instance, Lapwing Vanellus vanellus, part of the farmland bird indicator, is supposed to decline as a result of climate change. Increasing numbers of predators and invasive species might also be important. How can we be sure that declining trends in farmland birds are driven really by changes in farmland and not by other forces?
AnswerWe can never be 100% sure that declining trends in farmland birds are really driven by changes to farming, but on the balance of evidence available at this time, that is the most parsimonious explanation. Indeed, there is compelling and ample evidence to show that the intensification of agriculture has affected farmland bird populations deleteriously (for full review and supporting literature see: Wilson et al., 2009). We also recognise that many other factors, such as short- or longer- term changes in the weather/climate, migration strategy of the species, predation pressure, disease incidence, interspecific competition, and even alien invasive species, might all affect farmland bird populations in an integrated and complicated manner. However, the best evidence, of which there is a good deal across Europe, points to the central role of agricultural change in the decline of many farmland birds, as well as other farmland animals and plants. There is relatively little hard evidence to support alternative explanations for the wide-scale decline of farmland birds and other wildlife, though there are individual examples. A number of studies have shown that some long-distance migrant birds have declined more steeply than resident birds, regardless of the preferred breeding habitat in Europe. It is not known whether deteriorating conditions on the breeding grounds in Europe, or on passage, or wintering sites in Africa/Asia is responsible for the declines; it seems likely that a combination of factors is involved. We will continue to review the relevant evidence. A fact, that long-distance migrants among farmland birds have declined less than short-distance migrants and residents in Europe suggests that habitat changes on breeding grounds (i.e. within Europe) are more important for this group of species (Voří¹ek et al., 2010).
Note that recent climate change and climate warming in Europe, a pattern observed from the late 1980s, cannot explain the earlier precipitous decline of farmland birds in the 1970s and 1980s; change in agricultural practices around that time remains the most parsimonious explanation.
To take a practical example, in 1999 the RSPB purchased Hope Farm near Cambridge, a site with a simple arable crop rotation and associated bird community. Since acquisition, the number of breeding territories of the UK Government´s Farmland Bird Indicator species has more than doubled and species richness has increased. This has been achieved through the implementation of a suite of wildlife friendly measures that deliver food and nest sites for birds. At the same time, profits on the farm have also increased. Hope Farm shows how changing the way land is managed can reverse the fortunes of farmland birds.