A red kite (Milvus milvus) clone, which cross-hybridizes to a human minisatellite, reveals complex polymorphic patterns in members of the Accipitridae, a family of 217 species of birds of prey, which includes the kites, hawks and eagles. The total absence of hybridization to males implies that the sequence is located on the W chromosome, and stable inheritance from mother to daughter suggests that the patterns evolve as haploid matrilines. This has allowed not only the development of a simple and rapid sexing technique but may also provide a means of monitoring matriarchal success and dispersion. As an example, a survey of 36 continental European red kite nests revealed 24 different haplotypes, whereas only 2 were found among 53 Welsh nests. The results show the effect of a dramatic bottleneck in Wales and may provide evidence of recent introgression from the continent.