Risky business: boldness and neophobia vary with host specialization in two avian brood parasites

Abstract

Brood parasites have evolved unique morphological, physiological and behavioural traits to evade host defences and exploit host parental care. Key adaptations, such as rapid egg laying, egg mimicry and manipulative begging behaviour by chicks and fledglings, enable these species to maximize reproductive success. Brood parasites range from extreme host generalists to host specialists, with generalists encountering a broader range of ecological conditions and host behaviours than specialists. We examined the relationship between specialization in host use and behavioural traits often associated with personality in females of two closely related cowbird species: the generalist shiny cowbird, Molothrus bonariensis, and the specialist screaming cowbird, Molothrus rufoaxillaris. We predicted that shiny cowbird females would be bolder, less neophobic and more exploratory than screaming cowbird females. Through standardized experiments, we assessed risk aversion, neophobia and exploratory behaviour in 47 wild-caught shiny cowbird and 33 screaming cowbird females. Shiny cowbird females resumed feeding more quickly after a startling event and approached a feeder with a novel object more frequently than screaming cowbird females. However, we found no differences in exploratory behaviour between the two species. Our findings highlight the importance of considering the degree of host specialization when examining behavioural traits in brood parasites. Specifically, reduced neophobia in shiny cowbird females may facilitate their invasive capabilities, allowing them to successfully navigate novel environments and hosts.