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.

Signalling with a cryptic trait: the regularity of barred plumage in common waxbills.

Sexual signals often compromise camouflage because of their conspicuousness. Pigmentation patterns, on the contrary, aid in camouflage. It was hypothesized that a particular type of pattern-barred plumage in birds, whereby pigmented bars extend across feathers-could simultaneously signal individual quality, because disruptions of these patterns should be perceptually salient at close range and help assess plumage condition. Here we show that common waxbills (Estrilda astrild), which have extensive barred plumage, have more regular patterns as adults than as juveniles, and that adult males have more regular patterns than females. Both these differences are indicative of sexual signalling in species with conventional sex roles. More regular barred plumage was related to better body condition in adult males. Colour ornamentation traits were also related to aspects of quality, either the same as barred plumage (body condition) or a different one (good feather development), supporting both the 'redundant message' and the 'multiple message' hypotheses for the coexistence of multiple sexual signals. Although receiver responses to the regularity of barred plumage were not studied here, research on other species has shown that barred plumage can mediate social interactions. We conclude that using barred plumage as a signal of quality helps circumvent the functional compromise between camouflage and communication.