Populations of the Pin-tailed Whydah (Vidua macroura), native to sub-Saharan Africa, have greatly increased in southern California in recent years, prompting speculation as to which species serve as hosts to this obligate brood parasite. Field studies and opportunistic sightings during the summer of 2014 strongly suggest that the Scaly-breasted Munia (Lonchura punctulata), an introduced species also derived from the pet trade, is the principal host species in the region. We present evidence for this based on investigation of munia nests by female whydahs and several instances of adult munias feeding recently fledged whydahs. This novel host–parasite relationship implies that any potential spread of the Pin-tailed Whydah in North America is at least partly dependent on the distribution of the Scaly-breasted Munia.