Superb Fairy-wrens (Malurus cyaneus) increase vigilance near their nest with the perceived risk of brood parasitism

Brood parasites typically impose costs on their hosts, which select for host defenses. However, where defenses are costly, hosts can benefit by facultative expression of defenses in relation to the risk of parasitism. The results of our model-presentation experiments show that Superb Fairy-wrens (Malurus cyaneus) mediate vigilance around their nest according to their perceived risk of brood parasitism; when the risk of parasitism is high, they increase the time they spend in the vicinity of their nests. In combination with previous studies, these data suggest that Superb Fairy-wrens have a plastic defense portfolio that can be acquired rapidly and deployed facultatively to prevent parasitism while minimizing wasteful investment in defenses in the absence of parasitism.