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

Using published data, this study assesses whether population changes in Bri tish breeding birds over the 20-year period, 1968-88, have led to an overal l change in biomass. Because of uncertainty in the population estimates, th e most extreme estimates of biomass changes are a 6% increase and a 71% dec rease. However a parsimonious mid-range estimate suggests that, excluding s eabirds and Common Elder Somateria mollissima, bird biomass in Great Britai n has fallen from 14 200 tonnes in 1968 to 12 742 tonnes in 1988, a decreas e of 10%. If the Pheasant Phasianus colchicus is excluded from the calculat ions, the decrease becomes 29%. While most of the species contributing to t he decrease ave associated with farmland, the species that have increased i n biomass form a more heterogenous group, many being commensal with humans.