The Role of Learning and Behavioral Plasticity in Novel Brood Parasite-Host Interactions

Abstract

Nest parasitism is a growing field within behavioral biology. Obligate brood parasites lay their eggs into the nest of host species, abandoning their young and offloading the costs of parental care onto the hosts. Interactions between hosts and parasites are interesting to evolutionary biologists because they can reveal how natural selection favors the evolution of host defenses. The current literature underrepresents the evolution of these early-stage defenses. In this study, we observed the relationship between the parasite pin-tailed whydah (Vidua macroura) and its host the scaly-breasted munia (Lonchura punctulata). Their interactions began recently and are solely observed in California. This system presents an opportunity to observe the early stages of co-evolution of these two birds, potentially leading to the development of host defense mechanisms. We sought to determine whether the munias recognized whydahs as a threat, an antecedent to identifying and later counteracting the parasite. We conducted a playback experiment in which we exposed munias to both whydah and control (house finch) songs. The timed behaviors we observed were classified into either “reaction” or “no reaction” categories. Results from a paired Wilcoxon Signed-Rank test revealed that the whydah song produced a significantly higher “reaction” time than the control, mostly consisting of vigilant behavior. Our observations also detailed aggressive behavior from the munias towards the whydahs, which is remarkable as munias are not aggressive in their native range. These results suggest that munias have learned that pin-tailed whydahs are a threat, an example of behavioral plasticity leading to a frontline defense against brood parasitism. We were unable to determine whether munias are aggressive towards pin-tailed whydahs because they perceive them as a nest parasite, or because they are reacting to aggression by the whydahs in other contexts. Even so, we expect that these results will aid in addressing the gap in our understanding of the emergence of frontline defense mechanisms and provide the foundation for future research on this new and understudied host-parasite relationship.