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 data from the Common Birds Census over the period 1968-1991. Temporal trends in local abundance and occupancy are described and their covariation assessed on a species-by-species basis in both farmland and woodland habitats. For the most part, members of the Paridae have increased in abundance and occupancy over this period while members of the Sylviidae show a range of population trajectories. These associations are translated into positive intraspecific 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 of local abundance (and occupancy) within this habitat. Biological and non-biological explanations for this variance are discussed.