Trends in average number of introduced birds
The graphs below show trends in the national average number of introduced birds counted per garden each year from 2007 to 2013. The national average counts were derived from regional average counts weighted by the proportion of households in each of the 16 administrative regions of the country. The weighting was needed because the number of survey returns that came from each region was not in proportion to the number of households, and also because the percentage of survey returns that came from each region varied from year to year.
