Constant Effort Sites Scheme (CES)

CES is a national standardised ringing programme organised by the BTO. The same nets are operated each year in the same locations over the same time period at regular intervals through the breeding season. There are twelve 10/11 day intervals within which a CES ringing session needs to be run, starting in late April and ending in late August.

There are currently about 120 participating sites throughout the UK. CVRS started with CES in 1983 and over most of that time ran two separate CES sites but is currently only still running one of these.

CES takes priority over all other ringing. It is most important that no nets are set in CES sites during the three days immediately preceding each visit, but there are plenty of other well established net lanes that can be used instead.

Further information on CES, including the start and end dates for the 12 visit periods for the current year, can be found at The Constant Effort Sites Scheme (CES) | BTO - British Trust for Ornithology.