Does antiparasite behavior improve with experience? An experimental test of the priming hypothesis

Behavior is usually the first line of defense against parasites. Antiparasite behaviors, such as grooming, or outright avoidance, have been shown to reduce the risk of parasitism in a wide variety of host–parasite systems. However, despite the central importance of antiparasite behavior, little is known about the extent to which prior exposure to parasites improves effectiveness. Here, we report the results of a 2-year study designed to test whether exposure to parasites can "prime" behavior, loosely analogous to priming of the immune system. We tested whether preening improves with experience by infesting captive-bred rock pigeons (Columba livia) with 2 common species of rock pigeon feather lice. We infested "primed" birds in Years 1 and 2 of the study and "nonprimed" birds only in Year 2. Birds with lice preened about a third more, on average, than birds without lice. Birds subsequently cleared of lice resumed preening at the same rate as birds that never had lice. Thus, our results confirm that preening is an inducible, reversible defense that is partly triggered by the presence of lice. Surprisingly, primed birds did not differ significantly from nonprimed birds in the overall rate or the efficacy of preening. Primed and nonprimed birds preened at similar rates and had similar numbers of lice at the end of the study. Our results therefore provide little evidence that antiparasite behavior improves with experience, at least in the case of preening as a defense against feather lice.