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CES in Europe CES Methods Each year CES ringers are asked to make a standard number of visits to their site spread evenly between early May and late August. The same set of mist nets is erected in the same positions on each of the main visits. The total length of standard netting is decided by the ringer, but is typically 100-200m. Ringers are asked to operate their set of standard nets for at least six hours on each visit and to standardise their chosen duration. A typical regime (in Britain) would be to begin netting at dawn and continue until 1100hrs on each of twelve visits. The scheme has some flexibility and permits additional nets to be used during main visits, and also extra visits. Most constant effort sites are located in either wet or dry scrub, reedbeds or deciduous woodland. Sites in coniferous woodland are not accepted because rapid tree growth is likely to cause short-term changes in catching efficiency and the local bird community. Potential constant effort sites are proposed by volunteer ringers, and are generally accepted into the scheme as long as they are located in suitable habitats and are not considered to be undergoing major successional changes. The aim is to have a number of sites with a good geographical spread across the country, so that national figures may be usefully generated. In most schemes there is some level of habitat recording, so that some idea of the representativeness of sites can be formed, and successional (and other) changes in vegetation structure and composition can be quantified. Data collection and routine analysis A certain minimum amount of information should be collected and, ideally, this should be submitted in electronic form by the ringers, or computerised later. The basic information to be collected for each bird includes: ring number, species, age, sex (where appropriate) and date(s) of capture. Additional information on biometrics, moult and breeding status (for example extent of brood patch in females) can usefully be collected and broadens the scope of possible analyses. In Britain and Ireland, the availability of software for submitting ringing data (IPMR, developed by a volunteer ringer) means that the majority (>95%) of CES capture data are submitted electronically via email or computer disc. The small number of paper submissions are computerised and checked by BTO staff. Using changes in standardized catch sizes we are able to measure long-term changes in the abundance of adult and juvenile birds. Long-term changes in catches of songbirds are of much greater conservation interest than annual fluctuations, which may be linked to particular weather events, for example. The indices of abundance and productivity generated by CES ringing have been compared to those other schemes, especially in Britain where many years data are available, to assess their validity. For most species long-term changes in the number of adult birds caught on CES sites are very similar to changes in the numbers of territories counted on Common Birds Census (CBC) plots, suggesting that such standardised mist-netting is a reliable method for assessing extensive changes in songbird populations (Crick et al. 2004). Similarly, the percentage of juveniles in the catch is a good indicator of overall breeding success. Several intensive studies have shown that annual catches of young birds in CES mist-nets do accurately reflect local breeding success (e.g. du Feu & McMeeking 1991). Many passerines show strong site fidelity to breeding sites in successive breeding seasons, so regular sampling of breeding birds can be an effective means of generating between-year recaptures which can be used to estimate survival (return) rates of adult birds. Although most of the well established schemes have a good number of sites participating, mark-recapture data from individual sites are often quite sparse and survival estimates for single sites often lack precision (Peach 1993). This combination of a large numbers of sites, each contributing relatively few individuals, provides large technical challenges for estimating survival rates. Recent advances in analytical techniques, however, allow mark-recapture data to be pooled across CE sites, which can lead to considerable improvements in precision. Work is now in progress to develop routine production of survival rate indices from the British CES scheme. Map of CES Schemes in Europe. Countries in dark green are the three longest-running schemes.
Summary of CES Schemes in Europe operating at June 2004. Details are given on the average number of sites operating in each year, the number of visits made and nets used at each site, together with an indication of whether they operate over the whole breeding season.
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