Intraspecific relationships between abundance and occupancy among species of Paridae and Sylviidae in Britain

Relationships between local abundance and occupancy of two groups of three bird species from the families Paridae and Sylviidae were examined using da ta from the Common Birds Census over the period 1968-1991. Temporal trends in local abundance and occupancy are described and their covariation assess ed on a species-by-species basis in both farmland and woodland habitats. Fo r the most part, members of the Paridae have increased in abundance and occ upancy over this period while members of the Sylviidae show a range of popu lation trajectories. These associations are translated into positive intras pecific abundance-occupancy relationships for all species on farmland, but for none in woodland. We speculate that the failure to establish abundance- occupancy correlations in woodland is due to greater variance in measures o f local abundance (and occupancy) within this habitat. Biological and non-b iological explanations for this variance are discussed.