The figure shows two trends.
1. Population trends of open farmland birds.
2. Population trends of farmyard and thicket.
Each of these two trends is divided into three time periods.
1. 1900 to 1960 based on little data.
2. 1960 to 1990 based on more data.
3. 1990 to 2023 based on standardized observations.

The last period contains the average index figures and a trend line calculated through them starts at 100 in 1990.