The genus "Milvus" contains two other species: the black kite ("M. migrans") and the yellow-billed kite ("M. aegyptius"). The red kite has been known to successfully hybridize with the black kite in captivity where both species were kept together, and in the wild on the Cape Verde Islands and infrequently in other places. The red kites on the Cape Verde Islands are (or rather were) quite distinct in morphology, being somewhat intermediate with black kites. The question whether the Cape Verde kite should be considered a distinct species ("Milvus fasciicauda") or a red kite subspecies has not been settled. A mitochondrial DNA study on museum specimens suggested that Cape Verde birds did not form a monophyletic lineage among or next to red kites. This interpretation is problematic: mtDNA analysis is susceptible to hybridization events, the evolutionary history of the Cape Verde population is not known, and the genetic relationship of red kites is confusing, with geographical proximity being no indicator of genetic relatedness and the overall genetic similarity high, perhaps indicating a relict species. Given the morphological distinctness of the Cape Verde birds and that the Cape Verde population was isolated from other populations of red kites, it cannot be conclusively resolved as to whether the Cape Verde population was not a distinct subspecies (as "M. migrans fasciicauda") or even species that frequently absorbed stragglers from the migrating European populations into its gene pool. The Cape Verde population became effectively extinct since 2000, all surviving birds being hybrids with black kites.