This national survey is ongoing.
The BTO's Heronries Census has gathered nest counts annually since 1928 at an increasing proportion of the UK's heronries. The aim is to count as many heronries as possible each year and to ensure that newly established sites are quickly discovered and brought into the programme of annual counts.
The main species covered is Grey Heron, but Little Egret is fully included, as are rarer species of colonial water birds such as Cattle Egrets (which nested in the UK for the first time in 2008). Nest counts of Cormorants are also collected, especially where they are nesting alongside herons. Data are shared with county recorders and for rare species with the Rare Breeding Birds Panel.
In the Herts BTO region (which includes the Essex side of the Lea Valley), the known heronries are: -
Amwell NR, Great Hardmead Lake
Nether Hall GPs
Holyfield Lake, Lea Valley CP
Cheshunt GP, Bowyers Water
Waltham Abbey Woods, Perme North
Brocket Park, Lemsford
Stanborough Lakes, Welwyn Garden City
Verulamium Park, St Albans
Stockers Lake, Rickmansworth
Marsworth & Tringford Reservoirs, Tring
Wilstone Reservoir, Tring
Frogmore Lakes nr Radlett
Aldenham CP, Elstree
Additionally, former/existing sites at Luton Hoo Park (Beds) and Bourne End (Berkhamsted) are on the Herts BTO region list of sites but have no recent data. I would be grateful if someone would like to check these locations for the presence of breeding Herons, and potentially take on counting any active colony if present.
If anyone is aware of Grey Herons, Little Egrets or Cormorants breeding at a site not listed above, or would like to get involved with the Heronries Census, please contact Murray Orchard at firstname.lastname@example.org