Trends in farmland bird populations in Member States with a higher share of intensive agriculture
The curves should not be compared by index value, but by the slope of the curve in year intervals. The population index value is centred on the average (i.e. the index values are lying close to 100). Source for country agricultural intensification ranking Donald P.F., Green R. E. and Heath M. F. 2001. Agricultural intensification and the collapse of Europe's farmland bird populations. Proc. R. Soc. Lond. 268, 25-29.