Clutch destruction and replacement are sometimes observed during studies of cavitynesting birds. This could be due to abandonment by the first female to lay, with subsequent replacement by another female, or to male infanticide. Clutch replacement is accompanied in some cases by evidence of aggressive competition between females and of destruction of eggs/hatchlings immediately prior to a new clutch being laid. This may indicate that clutch replacements are in fact nest take-overs by females after eviction of incumbent females. In the course of long-term studies of pied flycatchers Ficedula hypoleuca iberiae in central Spain, I have found evidence of clutch destruction through egg burial and ejection and replacement during laying or incubation, as well as of female-female aggression. No male involvement has been detected. Clutch replacements occur with a frequency that depends on the density of available nest-boxes and is positively associated with the rate of nest-box occupation by the same or other species. Moreover, clutch replacements can be accompanied by female wounds or death and involve clutch destruction in all cases. Putative replacers within the area of highest occupation frequently display the white forehead patch that is more typical of males, which may thus be associated with social dominance in females in Iberian populations. Clutch replacements in cavity-nesters should be studied in detail to confirm whether they represent cases of nest take-overs by competing females.