Changes in the biomass of birds breeding in Great Britain, 1968-88

Using published data, this study assesses whether population changes in British breeding birds over the 20-year period, 1968-88, have led to an overall change in biomass. Because of uncertainty in the population estimates, the most extreme estimates of biomass changes are a 6% increase and a 71% decrease. However a parsimonious mid-range estimate suggests that, excluding seabirds and Common Elder Somateria mollissima, bird biomass in Great Britain has fallen from 14 200 tonnes in 1968 to 12 742 tonnes in 1988, a decrease of 10%. If the Pheasant Phasianus colchicus is excluded from the calculations, the decrease becomes 29%. While most of the species contributing to the decrease ave associated with farmland, the species that have increased in biomass form a more heterogenous group, many being commensal with humans.