Haemosporidian infections influence risk-taking behaviours in young male blackcaps, Sylvia atricapilla

Abstract

Animal behaviour becomes essential to the dynamics of parasitism if some behaviours favour pathogen transmission or increase exposure to infection. Infections may also influence host behaviour when health and future fitness are compromised, which predicts infected individuals will adaptively change risk-taking behaviours. We studied whether haemosporidian infection influences exploratory, foraging and antipredator behaviours of male young blackcaps before their first migration. The study was conducted in captivity using subjects of a medication experiment with the antimalarial drug primaquine, which had temporarily cleared parasite blood stages of treated individuals 1 month before. In an initial exploration test in a cage unknown to the birds, infected birds started exploring earlier than uninfected ones. Risk-taking behaviours were further assessed in a sequence of tests starting with the opening of new feeders to induce a startle response, and continuing with simulations of increased predation risk. We first challenged birds with acoustic cues of predation risk by playing recorded conspecific alarm calls, using heterospecific song as a control for the reaction to sound. Then, we challenged birds with visual cues of risk, showing them a taxidermic sparrowhawk and a bottle as a control for the reaction to an unspecific threat. Uninfected birds showed appropriate sentinel behaviour, turning around more frequently in the presence of the sparrowhawk compared to the bottle, while infected birds tended to behave similarly when faced with both stimuli, a behavioural difference that was driven by individuals with single parasite infections. Throughout the trial, infected medicated individuals tended to alarm-call more often than infected unmedicated individuals, a weak effect of medication which was not observed in parasite-free birds. Our results show that haemosporidian infections can influence blackcap risk-taking behaviours and support the view that host behavioural repertoires are broadly associated with parasitism.