Heronries Surveys

As a predator at the top of the freshwater food chain, Grey Herons are excellent indicators of environmental health in the countryside. Other colonial heron species, most notably Little Egrets, require monitoring as actual or potential colonists in the UK.

BTO monitors these species through programmes of counts of 'apparently occupied nests' at colonies.

The Heronries Census began in 1928 and is the longest-running breeding-season monitoring scheme in the world. The aim of this census is to collect annual nest counts of herons from as many heronry sites as possible in the United Kingdom. Volunteer observers make counts of apparently occupied nests at heron colonies each year. Changes in the numbers of nests, especially over periods of several years, are a clear measure of the population's trend. The main species covered is Grey Heron Ardea cinerea but Little Egrets Egretta garzetta, which since 1996 have been nesting in a growing number of English and Welsh heronries, are fully included, as are rarer species of colonial herons such as Cattle Egrets Bubulcus ibis (which nested for the first time in Somerset in 2008). Even single nests of any these normally colonial species are relevant to the Heronries Census.

BTO also undertakes periodic Heronries Surveys which expand upon the annual coverage of the ongoing Heronries Census. Heronries Surveys (of varying aims and scope) have been undertaken in 1928, 1954, 1964, 1985 and 2003.

The main output from these heronries counts is the modelled trends of Grey Heron population size, presented in the BTO's 'Wider Countryside' report (birdtrends). Numbers have been rising long-term in England, Scotland and Wales, reaching a UK peak in 2001.

If you know of a place where herons breed (in the UK) that may not be being counted annually for the Heronries Census, or if you would like to contribute to counting herons' nests, please contact your local Regional Representative or John Marchant (email: ) at BTO HQ.

You can help by making a donation to the Heronries Appeal.
£40,130 has been raised (as of 01/09/05). Thank you.