This year marks the 90th anniversary for the British Trust for Ornithology's (BTO) Heronries Census, which has been carried out annually since 1928 and represents the longest-running dataset for any breeding bird in the world.
The census started out as a one-off survey for the journal British Birds and currently covers around two-thirds of the UK’s heronries annually.
The long-term trend since 1928 shows a slow but small increase in Grey Heron numbers. The survey also charts the effect that severe winter weather has had on the species’ population over the years. The hard winter of 1962-63 produced the largest dip, but currently Grey Heron has yet to fully recover from the cold winters of 2008-09 to 2010-11.
Ian Woodward, Heronries Census Organiser at the BTO, said: “Thanks to the volunteers who have taken part in the census over the years, we have a very good picture of where our heronries are and, more importantly, how they are doing. However, more recently we have also been able to chart the rise of Little Egrets breeding here in the UK, many of which have joined our Grey Heron colonies.”