THE EFFECT OF MIGRATION AND SCALE ON THE STUDY OF BIRD POPULATIONS - 1991 WITHERBY LECTURE

Birds are highly mobile animals and we need to understand the factors and processes that determine numbers throughout their range and annual life cycle. Most avian studies have concentrated on birds using one locality at a particular time of year, but the numbers breeding or wintering in any one locality may be affected by the size of the greater population of which the local group forms a part, as well as by local conditions. Equilibrium theory provides a useful framework within which to analyse populations at this larger scale, although the meaning and usefulness of some of the concepts used for investigating local groups may change. New approaches are required in which mathematical models are used to integrate the results of studies on the behavioural and population ecology of local groups with those of large-scale monitoring programmes of the kind conducted by the BTO.