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Constant Effort Sites
The Constant Effort Sites (CES) scheme is a national standardised ringing programme set up by the British Trust for Ornithology and has been running since 1983. The CES scheme uses catches from standardised mist-netting to monitor key aspects of the demography of 28 common breeding songbirds. All sites in the scheme follow the national methodology of putting up the same number of nets, in the same sites and at the same intervals throughout the breeding season, so that the catches reflect, as far as possible, the natural abundance of bird species in the area. Changes in the total number of adults caught provide a measure of changing population size, while the proportion of young birds caught forms an index of breeding success. Retraps of adult birds ringed in previous years are used to estimate annual survival rates. Individual site data is fed into the national database, which allows fluctuations due to local influences to be ‘smoothed’ and species caught locally in small numbers to be meaningfully analysed. Constant effort ringing schemes similar to the one run by the BTO have now been set up in several European countries as well as the USA, adding an international perspective to this successful monitoring tool.
The
first of the groups CES projects began in 1984 at West Thurrock Marsh
on the north bank of the Thames. This site was first used by the group
in 1977 and a regular ringing program continued there until 1987 when
the site was developed as a shopping centre and industrial park. In 1987
the group started a new CES project at Littlebrook Power Station near
Dartford in Kent, where the study ran from 1989 to 1996. This site was
the original home of the group and had been used as a study area since
1968 until it became untenable due to vandalism and the impending development
of the area as a science park. More recently the group has embarked on
two new CES studies; the first at the Jeffery Harrison Reserve at Sevenoaks,
Kent was started in 2000; the
secord was started in 2003 at Crossness Nature Reserve, Thamesmead, Greater
London and both are beginning to provide a useful insight into the population
dynamics of the local bird populations, as well as adding valuable data
to the national picture.
For details of the 2005 or 2006 CES results please click on one of the links below.
Want to learn more about CES? Click this link to the BTO web site.