Behavioral and morphological responses to perceived predation risk: a field experiment in passerines

Predators can affect prey both directly (consumptive effects) and indirectly (nonconsumptive effects), with a growing body of literature showing the latter may have pronounced effects. Prey populations are comprised of individuals that differ in perception of and willingness to take risk; therefore, studying how different types of individuals respond to predation risk is necessary to fully understand prey dynamics. Playbacks were used to experimentally manipulate perceived predation risk in nest-box populations of wild great tits (Parus major) to examine the nonconsumptive effects of avian predators on prey behavior and morphology, and to explore individual differences in prey response. Individuals responded to our treatment, and responses differed depending on both treatment and pre-manipulation behavioral type. Birds in areas exposed to predator playback tended to decrease in body mass more than birds exposed to nonthreatening (control) playback. Differences between treatment groups were mainly driven by initially fast exploring birds: In the control treatment, fast explorers increased in mass, whereas the initially fast exploring birds in the predation treatment decreased in mass. Furthermore, birds exposed to predator playback decreased exploratory tendency compared with controls. These findings demonstrate that predation risk alters great tit behavior (exploration) and morphology (body mass) and that plasticity in response to risk relates to an individual's willingness to take risks. Our findings suggest that individuals differ in susceptibility to predation risk, causing adaptive individual differences in responsiveness to changes in predation risk. Acknowledging individuality in responses to perceived predation risk has important consequences for understanding prey dynamics.