Haemosporidian parasites missed the boat during the introduction of common waxbills (Estrilda astrild) in Iberia.

Exotic species can experience fast expansion in new environments, especially if they left their pathogens behind (Enemy Release hypothesis) or brought novel pathogens to the native competitors (Novel Weapon hypothesis). Common waxbills (Estrilda astrild) are native to sub-Saharan Africa and invaded west Iberia since the 1960s. Past haemosporidian parasite surveys at four locations in Portugal showed that waxbills can be infected with parasites, though with very low prevalence. However, it is not known if this pattern generalizes across their distribution range, or if there are geographic differences in parasite prevalence. It is also not discussed if this is a case of Enemy Release, as opposed to waxbills being also little parasitized in their native range. We screened 617 waxbills in 23 sites in Portugal and detected nine parasite lineages, most of them only known to the Palearctic. Only ten individuals were parasitized, and there was no significant geographical pattern on the prevalence. Overall, this population shows very low prevalence of haemosporidians (1.6% prevalence), which contrasts with significantly higher prevalence in native grounds, as compiled from the literature. These data support Enemy Release as the most likely hypothesis, which may have been important for their success as an exotic species.