O'Connor R.J. (1980) Pattern and process in Great Tit Parus major populations in Britain. ARDEA 68 (1-4): 165-183

The population dynamics of the Great Tit Parus major through the whole of Great Britain are investigated using a new approach to such studies: the integration of extensive data on relevant aspects of the biology of the species collected independently by the largely amateur membership of the British Trust for Ornithology. Annual data on the size of the territorial population of Great Tits have been obtained from approximately 100 farmland plots since 1962 and from approximately 80 woodland plots since 1964, using the mapping method of censussing. These results suggest the woodland population is regulated by density-dependent factors, with farmland (and possibly other habitats) serving to some extent as buffer habitats. Analysis of breeding performance (monitored in the BTO's Nest Records Scheme) showed that clutch size was steeply and negatively density dependent, with over 60 per cent of the variation in annual mean clutch size correlated with population density. Average hatching success was independent of population level but the proportion of total clutch losses decreased with density, implying that birds breeding in these years were more likely to hatch at least some young. Nestling rearing success also decreased with population density. Ringing data showed that full-grown birds ringed in a high population year were less likely to survive for a further 400 days than those ringed in a low population year. Pulli showed a trend in the same direction. This pattern was largely due to females surviving well at low densities and poorly at high densities whilst males experienced a relatively constant mortality risk at all densities. Both sexes showed relatively more frequent long distance (above 10 km) movements at high population densities. Great Tits were more likely to overwinter successfully when November temperatures were high than when low and when fewer birds resorting to artificial feeders in gardens than when many did so (because natural foods had run out?). The temperature dependence was close to that expected in Britain for a bird of Great Tit size and was independent of the dependence on artificial feeders. These findings are generally consistent with or represent extensions of the results of the Oxford study of the species and suggest the technique of mass data analysis can be applied safely to less well-studied species.