Flights of fear: a mechanical wing whistle sounds the alarm in a flocking bird (original) (raw)
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Alarming features: birds use specific acoustic properties to identify heterospecific alarm calls
Vertebrates that eavesdrop on heterospecific alarm calls must distinguish alarms from sounds that can safely be ignored, but the mechanisms for identifying heterospecific alarm calls are poorly understood. While vertebrates learn to identify heterospecific alarms through experience, some can also respond to unfamiliar alarm calls that are acoustically similar to conspecific alarm calls. We used synthetic calls to test the role of specific acoustic properties in alarm call identification by superb fairy-wrens, Malurus cyaneus. Individuals fled more often in response to synthetic calls with peak frequencies closer to those of conspecific calls, even if other acoustic features were dissimilar to that of fairy-wren calls. Further, they then spent more time in cover following calls that had both peak frequencies and frequency modulation rates closer to natural fairy-wren means. Thus, fairy-wrens use similarity in specific acoustic properties to identify alarms and adjust a two-stage antipredator response. Our study reveals how birds respond to heterospecific alarm calls without experience, and, together with previous work using playback of natural calls, shows that both acoustic similarity and learning are important for interspecific eavesdropping. More generally, this study reconciles contrasting views on the importance of alarm signal structure and learning in recognition of heterospecific alarms.
Semantic communication in birds: evidence from field research over the past two decades
What do animal signals mean? This is a central question in studies on animal communication. Research into the semantics of animal signals began in 1980, with evidence that alarm calls of a non-human primate designated predators as external referents. These studies have challenged the historical assumption that such referential signaling is a unique feature of human language and produced a paradigm shift in animal communication research. Over the past two decades, an increasing number of field studies have revealed similar complexity in anti-predator communication of birds. The acoustic structures of avian alarm calls show a high degree of variation in pitch, duration, shape, and repetition rate. In addition to such distinct and graded variations, several birds combine discrete types of notes or calls into higher complex sequences. These variations in alarm calls are typically associated with the predator's attributes, such as predator type and distance, and receivers respond to them with appropriate anti-predator behaviors. Although alarm calls of several bird species, as well as those of monkeys , appear to denote predator attributes, almost nothing is known about the cognitive processes that underlie the production and perception of these signals. In this review, I explore the existing evidence for ref-erential signaling in birds and highlight the importance of the cognitive approach to animal communication research. I hope this review will promote further investigations of alarm-calling behavior in birds and will help enhance our understanding of the ecology and evolution of semantic communication.
Brain, Behavior and Evolution, 2019
Acoustic communication signals are typically generated to influence the behavior of conspecific receivers. In songbirds, for instance, such cues are routinely used by males to influence the behavior of females and rival males. There is remarkable diversity in vocalizations across songbird species, and the mechanisms of vocal production have been studied extensively, yet there has been comparatively little emphasis on how the receiver perceives those signals and uses that information to direct subsequent actions. Here, we emphasize the receiver as an active participant in the communication process. The roles of sender and receiver can alternate between individuals, resulting in an emergent feedback loop that governs the behavior of both. We describe three lines of research that are beginning to reveal the neural mechanisms that underlie the reciprocal exchange of information in communication. These lines of research focus on the perception of the repertoire of songbird vocalizations,...
Aerial alarm calling by male fowl (Gallus gallus) reveals subtle new mechanisms of risk management
Alarm calling is a classic problem in evolutionary biology. Although a signaller may increase the likelihood of survival for group members, which typically include kin and mates, there are inherent risks associated with any behaviour that increases conspicuousness to predators. Callers can increase their indirect benefits by calling only in the presence of an appropriate audience and manage concomitant costs by judicious investment. Possible tactics for controlling costs include facultative variation in call structure and timing, as well as sensitivity to the environmental and social factors that predict personal vulnerability. We examined individual variation in the alarm-calling behaviour of male fowl in naturalistic social groups. Previous studies of cost management have focused on variation at the level of alarm call rate. We took advantage of recent advances in wireless sound recording and remote video monitoring to test for more subtle variation in signal structure and timing. These were then mapped onto individual mating success and moment-to-moment changes in environmental and social context. Results replicate the previous finding that alarm calling is sensitive to both social rank and recent mating success. In addition, we detected systematic variation in call structure as a function of personal vulnerability and proximity to a rival male. The frequency bandwidth of alarms was reliably influenced by degree of vigilance prior to calling, suggesting that this acoustic dimension reflects motivational state. Taken together, these results reveal several novel tactics for risk management, complementing those previously described at the level of gross variation in alarm-calling behaviour.