The Constant Effort Sites scheme (CES) is amonitoring programme that is based on standardized mist-netting and provides data on population changes, productivity and survival of birds.The protocol was introduced in United Kingdom with the objective of 12 visits between May and August annually.This protocol was adapted for the Finnish(1986-) and Swedish (1996-) CES programmes. Annually, an average of 36 and 19 sites were active during the last decade in Finland and Sweden.

In 26 species-specific diagrams, the upper figure is the smoothed population index for each country. Both smoothers average to 1, so annual levels of abundance between the two countries are not directly comparable, but the trends are. The lower figure gives the annual productivity indices for Finland (blue) and Sweden (red) with reference year 2004 for both countries.

In summary, the population trends are generally similar between both countries and also generally similar with regard to trends derived from breeding bird survey data. Some interesting trend differences between the countries are evident, but the reasons for these differences are not easily explained.

Productivity seems to be in surprisingly close synchrony between many species – and between Finland and Sweden especially during the most recent years. Spring temperature has been shown to act as a key factor determining the productivity of boreal passerine populations.