Integrated Population Monitoring

Survey and monitoring form the bedrock for conservation. Without knowledge of the distribution and size of populations and how they are changing, the actions of conservationists must necessarily be based upon hunches and intuition that have a high chance of failing the species or habitats they wish to conserve.

Fortunately, for bird conservationists in the UK, there is a long tradition of volunteer support for ornithological surveys and monitoring, and the British Trust for Ornithology has been the medium for channelling much of these efforts towards well-structured programmes of increasing value. The statutory conservation bodies in the UK were farsighted enough to realise the superb cost-effectiveness of volunteer monitoring by contracting the BTO to provide monitoring data from the early 1960s. The Joint Nature Conservation Committee (JNCC) and its predecessor bodies have benefitted greatly from this work which provides it and the Country Agencies (English Nature, Scottish Natural Heritage, Countryside Council for Wales and the Environment & Heritage Service in Northern Ireland) with an unrivalled comprehensive overview of the long- term trends for a major component of the UK's wildlife. This overview covers changes in population size as well as changes in reproductive success and survival that might have caused the population changes. When a declining population is detected, the BTO can inform conservationists of which stage of the life-cycle appears to have been detrimentally affected. Conservationists are thereby able to target their action or further research effectively. This is the main function of the BTO's Integrated Population Monitoring programme for UK birds.

The Integrated Population Monitoring Programme has been developed by the BTO under the BTO/JNCC contract to monitor the numbers, breeding performance and survival rates of a wide range of bird species. It has the following specific aims:

1. To establish thresholds that will be used to notify conservation bodies of requirements for further research or conservation action.
2. To identify the stage of the life cycle at which changes are taking place.
3. To provide data that will assist in identifying the causes of change.
4. To distinguish changes in populations induced by human activities from those that arenatural population fluctuations.

The programme brings together data from several long-running BTO schemes. Changes in numbers of breeding birds are measured by the Common Birds Census, Waterways Bird Survey and Constant Effort Sites Scheme (based on bird ringing). The recently established BTO/JNCC/RSPB Breeding Bird Survey can only provide information on short-term population changes at the moment, but will gradually develop into the major component of this work. The Nest Record Scheme and Constant Effort Sites Scheme provide data on productivity, while the Ringing Scheme and Constant Effort Sites Scheme provide data on survival rates.

The value of combining results from different monitoring schemes

A current and important example relates to severe declines in the population size of 10-20 species of birds on farmland measured by the Common Birds Census over the past 15-20 years. This has identified a major problem in the wider countryside that has to be tackled by conservationists. While the problem has been identified, the causes of these declines could involve changes in productivity or in survival. Intensive studies of these 10-20 species would be very costly and may not necessarily be representative of the wider countryside because intensive study plots would be small. The existence of long-term BTO datasets has allowed us to tackle this issue immediately and has produced some very important results that will help to guide the conservation bodies in the future.

Results from the Nest Record Scheme have revealed which species have suffered declines in productivity that parallel declines in population size (e.g. Linnet). More detailed analyses can relatively quickly probe such preliminary results to show, for example, that every aspect of Corn Bunting and Skylark productivity per nesting attempt has increased markedly during their population declines. In this way the Nest Record Scheme has been able to direct conservation research towards investigating survival rates outside the breeding season for species such as Corn Bunting, but towards the nesting season for Linnet.

Similarly, BTO-led studies of the Lapwing population have shown that productivity declines and not changes in survival appear to have driven its population decline. Detailed analysis of the decline of the Song Thrush population has shown that declines in first-year survival rates were sufficiently large to account for the observed changes in population size; other aspects of survival and productivity have not varied sufficiently to have had a major impact. Analyses of declining Sedge Warbler populations using data from a variety of BTO monitoring schemes showed that changes in over-wintering survival, associated with below average rainfall in the Sahel wintering quarters, was the most important factor determining population change. Analyses of the population dynamics of seven Palaearctic-African migrant passerines have shown that over- wintering survival was the most important factor in all cases.

The value of the BTO's historical databases in helping to diagnose the problems facing these species will be invaluable and more cost-effective than initiating between 50 and 100 individual studies. Of course, this is not the only function of the BTO's Integrated Population Monitoring programme, because, once conservation actions have been initiated, their successes will be monitored and be assessed against the background information provided by the BTO's long-term schemes. This is the only way that conservation bodies can measure the effectiveness of their actions at a national scale in a cost-effective manner.