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

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 nes t-box plots in northern Belgium that vary in size. degree of isolation and population density. These plots have been studied for varying lengths of ti me over the past 40 yr. As expected, LR was higher among male than female b irds, and this difference was most pronounced in blue tits. Regardless of s pecies 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 insid e continuous Forest. suggesting that fragmentation reduces exchange among l ocal populations However, LR was not related to the degree of isolation of individual fragments. We also found a weak but significant increase in LR w ith productivity (number of nestlings) of plots: bur no relationship with o ther demographic variables.