Bird populations are perhaps the most visible, and certainly amongst the most popular, component of biodiversity in Europe. They also provide an easily studied indicator of environmental and land-use change. However, an understanding of why their populations change, and the environmental reasons underlying such changes requires a knowledge of the demography of the population, i.e. birth and death rates, in addition to simple changes in numbers (Baillie 1990). Ringing, particularly under standard conditions, can provide a useful estimate of each of these parameters.
With this in mind, a pilot constant effort ringing project was initiated in Britain in 1981, by a volunteer. In 1986, this became a nationwide project, the Constant Effort Sites (CES) Scheme run by the British Trust for Ornithology (Baillie et al. 1986). Sites participating in the Scheme employ a constant number of nets in the same locations for a standard number of visits each year. Using such a protocol, it is possible to monitor, on an annual basis, changes in:
- adult and juvenile abundance
- productivity (proportion of young birds caught each year)
- adult survival rates (from between-year recaptures).
In Britain, the CES Scheme forms part of an Integrated Population Monitoring (IPM) Programme, which incorporates the Breeding Bird Survey, Nest Record Scheme and national Ringing Scheme, which aims to identify the causes (natural and anthropogenic) of population changes affecting breeding birds in Britain and Ireland.
Following the development of CES ringing in Britain and Ireland, other ringing schemes across Europe set up their own constant effort projects including Finland (commenced in 1987), France (1989), Spain (SYLVIA, 1991) and The Netherlands (1984).
The MAPS (Monitoring Avian Productivity and Survivorship) program in North America was set up in 1989 and closely follows the BTO CES scheme protocols (De Sante et al. 1995, http://www.birdpop.org/nbii/ NBIIHome.asp).
Development of the EURO-CES project
A number of constant effort ringing schemes are now operated across Europe. At the EURING General Meeting on Helgoland in autumn 1999 there was considerable interest expressed by a number of Ringing Schemes in trying to standardise, as far as possible, such schemes across Europe. In addition to allowing schemes to learn from each other’s experiences, this will lead, ultimately, to the possibility of comparing trends in population dynamics between countries, and monitoring populations at a European scale. This is important because many of the factors that influence bird population dynamics (e.g. the climate change and the Common Agricultural Policy) operate at this broad scale.
This project is being led by the British Trust for Ornithology, in collaboration with the French Centre de Recherches sur la Biologie des Populations d’Oiseaux. This project has two main aims:
- To assess the current state of CES-type schemes in Europe and develop agreed protocols for CES fieldwork methodology, data exchange and analysis.
- To assess the potential for producing combined European trends / comparative national trends for a common suite of species.
Guidelines for operating CES in Europe, taking into account its wide latitudinal range have now been developed and early analyses have provided encouraging signs that results from schemes in each country can be combined in a Europe-wide analysis.