Local recruitment of great and blue tits (Parus major, P. caeruleus) in relation to study plot size and degree of isolation

Abstract

Few studies are available that analyse variation in dispersal rates between populations. Here we present data on the degree of local recruitment (LR) of great and blue tits (Parus major, P. caeruleus) in a large number of nest-box plots in northern Belgium that vary in size, degree of isolation and population density. These plots have been studied for varying lengths of time over the past 40 yr. As expected, LR was higher among male than female birds, and this difference was most pronounced in blue tits. Regardless of species and sex, more local recruits were found in larger plots but also in plots with a higher population density. Thus, LR increased with population size (number of pairs) but levelled off in the largest populations at ca 50%, for male birds. LR was higher in forest fragments compared to plots inside continuous forest, suggesting that fragmentation reduces exchange among local populations. However, LR was not related to the degree of isolation of individual fragments. We also found a weak but significant increase in LR with productivity (number of nestlings) of plots, but no relationship with other demographic variables.