The effects of the number of nests within a neighboring space on reproductive success were examined in Egretta garzetta and Ardea cinerea in a heronry. Two neighboring spaces were defined: (i) the Neighborhood is a space enclosed by a sphere of radius DN whose center is located at a focal nest; (ii) the Surrounding is a space enclosed by a sphere of radius DS (DS > DN) that excludes the Neighborhood. DN and DS were set at several different values. The number of nests in the Neighborhood had a significant negative effect on reproductive success when DN = 0.5 m for E. garzetta and when DN = 1.5 m for A. cinerea . The number of nests within the Surrounding had a significant positive effect on the reproductive success of A. cinerea when DN = 1.5 m and DS = 3 m or DS = 4.5 m. These results suggest that to examine individual differences in reproductive success within colonies, we should choose the appropriate Neighborhood and Surrounding to detect the effects of interactions among neighboring individuals.