The breeding distribution and abundance of the rook (Corvus frugilegus L.) in Great Britain since the 1920s

A dramatic decline in the breeding density of the rook ( Corvus frugilegus ) took place in Great Britain between 1944/6 and 1975. This was evident from the results of two national surveys conducted in these years and other more local censuses undertaken in the intervening period. The most notable decreases occurred in the eastern counties of England: Cambridgeshire (68%) and Lincolnshire (72%). Data from local surveys indicated that the decrease in rook breeding densities began in the late 1950s and continued into the 1960s. There were regional variations in the timing of this decline.
Regional variation in the breeding density of the rook and rookery distribution was analysed for the two national censuses. The pattern was shown to be similar for both periods, despite the fall in overall densities. Rooks occupied lowland (< 300 m) agricultural land and avoided areas of high human population. Higher rook densities and rookery sizes were consistently found in Scotland compared with England and Wales.