Non-Redundant Social Information Use in Avian Flocks with Multisensory Stimuli

Speedy revelations: how alarm calls can convey rapid, reliable information about urgent danger

In the perpetual struggle between high-speed predators and their prey, individuals need to react in the blink of an eye to avoid capture. Alarm calls that warn of danger therefore need to do so sufficiently rapidly that listeners can escape in time. Paradoxically, many species produce more elements in their alarm calls when signalling about more immediate danger, thereby increasing the reliability of transmission of critical information but taking longer to convey the urgent message. We found that New Holland honeyeaters, Phylidonyris novaehollandiae, incorporated more elements in alarm calls given to more dangerous predators, but video analysis revealed that listeners responded in 100 ms, after only the first element. Consistent with this rapid response, the acoustic structure of the first element varied according to the danger, and playbacks confirmed that birds need hear only the first element to assess risk. However, birds hid for longer and were more likely to flee, after calls with more elements. The dual mechanisms of varying both element structure and number may provide a widespread solution to signalling rapidly and reliably about immediate danger.

The role of complex cues in social and reproductive plasticity

Phenotypic plasticity can be a key determinant of fitness. The degree to which the expression of plasticity is adaptive relies upon the accuracy with which information about the state of the environment is integrated. This step might be particularly beneficial when environments, e.g. the social and sexual context, change rapidly. Fluctuating temporal dynamics could increase the difficulty of determining the appropriate level of expression of a plastic response. In this review, we suggest that new insights into plastic responses to the social and sexual environment (social and reproductive plasticity) may be gained by examining the role of complex cues (those comprising multiple, distinct sensory components). Such cues can enable individuals to more accurately monitor their environment in order to respond adaptively to it across the whole life course. We briefly review the hypotheses for the evolution of complex cues and then adapt these ideas to the context of social and sexual plasticity. We propose that the ability to perceive complex cues can facilitate plasticity, increase the associated fitness benefits and decrease the risk of costly 'mismatches' between phenotype and environment by (i) increasing the robustness of information gained from highly variable environments, (ii) fine-tuning responses by using multiple strands of information and (iii) reducing time lags in adaptive responses. We conclude by outlining areas for future research that will help to determine the interplay between complex cues and plasticity.