Comparative abundance of centipedes on organic and conventional farms, and its possible relation to declines in farmland bird populations

The aim of this study was to compare the abundance, species richness and diversity of centipedes on organic and conventional farms. These comparative data are relevant to the 'invertebrate food supply hypothesis' relating to the cause(s) of the marked declines in the abundance of farmland bird species that have been observed over the last few decades. Twelve pairs of organic and conventional farms spread across England and Wales were surveyed. Centipedes were used as an 'indicator taxon' for reasons elaborated in the text. The same species were present on organic and conventional farms. Also, species richness and diversity were broadly similar between the two farm types. The overall density of centipedes was significantly higher in the field margins of organic farms compared with conventional farms. However, densities in woodlands adjoining the two farm types were similar. This pattern is consistent with the effect of pesticides with limited lateral spread on arthropod populations in and close to the areas sprayed. It is argued that a decline in invertebrate density due to pesticide use is one of a number of factors contributing to the overall declines in farmland bird populations that have been observed.