Using long-term ornithological studies in setting targets for conservation in Britain

Long-term studies are necessary in conservation work for two main purposes: monitoring of population parameters, and defining habitat requirements to set targets for conservation action. Apart from their intrinsic interest, birds may be of value also as a means of monitoring the wider environment. Current developments include the integration of measures of breeding performance and survival with those of population size. This will also aid early warning of changes. The range of normal variation in these measures needs assessment to identify limits beyond which action is needed. Monitoring studies need to be reported in appropriate habitat or geographical units, but cover as wide a geographical area as possible in a coordinated manner, to provide context. Long-term studies are required for defining requirements, as needs may vary with overall population size, weather conditions, and other features which differ between years. Population studies based on age-structures at a moment in time may not be a good approximation of the real performance as assessed by following age-cohorts through time. This may be especially so in rare species. For these, sample sizes also present problems in short studies. Long-term studies may be required also to identify the needs of less obvious components of populations, such as immature individuals.