Intraspecific brood parasitism occurs commonly in a large number of bird species. Recent work shows that females parasitize the parental care of conspecifics either as a 'best-of-a-bad-job' strategy or as part of a superior reproductive strategy. A number of parasite and host behaviours, which either facilitate or prevent intraspecific brood parasitism, are similar to those occurring among interspecific brood parasites and their hosts.