What are the likely causes of the decline in the farmland bird indicator?
The European farmland bird indicator has declined by nearly 50% since 1980. A change in farming practices towards more intensive and specialised agricultural methods over a number of decades with an associated loss of hedgerows and marginal semi-natural habitats, along with changes in cropping patterns and increased use of fertilizers and pesticides, are all thought to have contributed to the large-scale decline of farmland bird populations in Europe. These changes have impacted upon the farmland birds´ nesting habitats and food resources. Evidence also suggests that increased predation may affect some ground-nesting species to a degree, such as waders and game birds, but is unlikely to have driven the decline of songbirds and the wider decline of farmland birds. Note also the likely interaction between predation and habitat management such that increasing predation rates may be caused by, or exacerbated by, the effects of agricultural change. See Wilson et al. (2009) for a full review.
The farmland bird indicator contains birds that are long-distance migrants. Studies have shown that some long-distance migrant birds have declined more steeply than resident birds. 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. However, an analysis of European trends of farmland birds has shown, that among this group of species, long – distance migrants have declined less than short – distance migrants and residents (Voříšek et al., 2010).