 Some 600 species (a quarter of the total) are known from a single record from a single host.Over 94% of species are associated with mammalian hosts, and only about 3% of species can be considered to be specific parasites of birds.The fleas on birds are thought to have originated from mammalian fleas; at least sixteen separate groups of fleas switched to avian hosts during the evolutionary history of the Siphonaptera.