We can never be 100% sure that farming changes really drive declining trends in farmland birds. Still, 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 agriculture’s intensification has affected farmland bird populations deleteriously (for full review and supporting literature, see: Wilson et al., 2009). We also recognize 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, 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 and 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. Several 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 unknown whether deteriorating conditions on the breeding grounds in Europe, or the passage, or wintering sites in Africa/Asia are responsible for the declines; it seems likely that a combination of factors is involved. We will continue to review the relevant evidence. The 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 (Voříšek 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 simple arable crop rotation and associated bird community. Since the 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 by implementing 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.