BTO Heronries Census - 90 not out

23 Mar 2018 | No. 2018-08

2018 marks the 90th anniversary for BTO’s longest running survey, which has been carried out annually since 1928, and represents, as far as anyone is aware, the longest running dataset for any breeding bird in the world.

The Heronries Census started out as a one-off survey for British Birds magazine but from small acorns mighty oaks do grow and currently around two-thirds of the UK’s heronries are covered annually by the census.

The long-term trend since 1928 shows a shallow increase but it also charts the effect that severe winter weather has had on the population over the years. The hard winter of 62/63 produced the largest dip but currently Grey Herons have yet to 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.”

For much of the history of the census Grey Heron has been the only species of interest; however, with the expansion of other heron species from elsewhere in Europe, such as Little Egret, this is likely to change to perhaps include Spoonbill, Great White Egret and Cattle Egret too.

The annual census is supplemented by periodic national surveys; the last full survey of heronries was carried out in 2003. To mark the 90th anniversary BTO is carrying out another comprehensive national survey and is asking birdwatchers to also visit historical sites which may not have been visited in recent years. Those who are interested can view the vacant sites map on the BTO website (

BTO is also asking birdwatchers to tell them about any heronries they see; this will help identify those that aren’t currently covered, adding even more information to this incredibly long-running study. Heronries can be added by clicking on the location in the vacant sites map.

Notes to editors  
1. The long-term Grey Heron trend graph is available from press [at]

2. The BTO is the UK's leading bird research charity. A growing membership and up to 60,000 volunteer birdwatchers contribute to the BTO's surveys, collecting information that underpins conservation action in the UK. The BTO maintains a staff of 100 at its offices in Thetford, Stirling, Bangor (Wales) and Bangor (Northern Ireland), who analyse and publicise the results of surveys and projects. The BTO's work is funded by BTO supporters, government, trusts, industry and conservation

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