Anglian Water/BTO Birds on Waste Water Treatment Works Project

Anglian Water (AW) asked us to study the birds found on a selection of their 1000 Waste Water Treatment Works (WWTW). The AW region is vast, stretching from the Humber in the north to south Essex in the south, the whole of East Anglia and as far west as Rutland and Northampton. Between September 2001 and September 2002 a dedicated band of volunteers, both from BTO and AW, took part in this survey recording the birds and the habitats available on their chosen sites.

During the course of the survey visits were made in the summer and winter so that we got a complete picture of bird use of the sites throughout the year. All the birds encountered using the sites were recorded, and habitat information was also collected during an initial visit. This has allowed us to look at the bird-habitat relationships within these WWTW throughout the year and pinpoint the most important habitats.

In all, 35 sites were covered in the winter and 25 during the summer. The major variation between the sites was in size – from tiny village sites to large urban ones serving major cities. An amazing 123 species were recorded in total, including such surprises as American Wigeon, Jack Snipe, Ruff and Whooper Swan, although the species richness varied dramatically from just 9 species to 81. Perhaps unsurprisingly species richness tended to increase with increasing size of site, and also with increasing habitat diversity, however, there was no significant correlation between site size and habitat diversity. What this means is that even on the smallest sites increased habitat diversity will have a positive effect upon species richness.

One exciting method of analysis we used involved combining data from this project with that from another BTO survey. We compared the species visiting the Treatment Works sites in summer with BBS (Breeding Bird Survey) data for the same areas. From this comparison we discovered that Pied Wagtail, the commonest species on the WWTW, is not even in the ‘top-ten’ in the surrounding countryside, and Starling was ranked seventh most common species on the WWTW list, and yet tenth on the BBS list. It emerged that a number of species on the red or amber ‘Birds of Conservation Concern’ list were also more frequently recorded on AW sites than surrounding habitats. These include Tree Sparrow, Corn Bunting, Willow Tit, House Sparrow, Reed Bunting and Grey Wagtail.

Grassland proved to be an important and common habitat type, but on many sites almost all the grass is regularly cut. Those sites that did have areas of longer grass attracted many more pipits, wagtails and thrushes, and a management routine that means cutting only part of the grass at WWTW could benefit both AW – who wouldn’t have to spend as much time and money on mowing - and the wildlife using the sites; a happy situation for both!

One fast declining habitat type traditionally associated with old-fashioned Sewage Farms were the flood meadows and areas of marsh and reeds. In modern works small, efficient filters take the place of the large meadows, which has led to a loss of these valuable wet areas. Nowadays, however, once the essential cleaning processes have taken place on the waste water some sites send the water through an additional ‘tertiary’ process, which does, in fact, involve soaking through a wet meadow or reedbed. The larger sites that have tertiary meadows could well benefit from having specific site management plans drawn up to make the most of the available habitats and improve them for birds and other wildlife.

Other important habitats that are found on many of the works include scrub patches and hedgerows, both associated with typical birds, such as warblers and Turtle Doves. Buildings provided nesting sites for Blue Tits and Swallow, and the rotary filter beds – such a feature of modern works, and the only installation common to ALL the sites visited – are important feeding grounds for Pied and Grey Wagtails, Starlings and gulls.

A full-colour leaflet, written by BTO and funded by AW called ‘Creating and managing habitats for birds on Waste Water Treatment Sites’ has been produced using the results of this project.

Thank you to all the volunteer observers from BTO and AW who undertook the fieldwork, and to Andy Brown and David Quincey of Anglian Water. This project was funded by Anglian Water.

For further information on this project, or to request a copy of the leaflet, please contact