Alert signals enhance animal communication in “noisy” environments

Abstract

Environmental noise that reduces the probability that animals will detect communicative signals poses a special challenge for longrange communication. The application of signal-detection theory to animal communication lead to the prediction that signals directed at distant receivers in noisy environments will begin with conspicuous "alerting" components to attract the attention of receivers, before delivery of the information-rich portion of the signal. Whether animals actually adopt this strategy is not clear, despite suggestions that alerts might exist in a variety of taxa. By using a combination of behavioral observations and experimental manipulations with robotic lizard "playbacks," we show that free-living territorial Anolis lizards add an "alert" to visual displays when communicating to distant receivers in situations of poor visibility, and that these introductory alerts in turn enhance signal detection in adverse signaling conditions. Our results show that Anolis lizards are able to evaluate environmental conditions that affect the degradation of long-distance signals and adjust their behavior accordingly. This study demonstrates that free-living animals enhance the efficiency of long-range communication through the modulation of signal design and the facultative addition of an alert. Our findings confirm that alert signals are an important strategy for communicating in "noisy" conditions and suggest a reexamination of the existence of alerts in other animals relying on long-range communication.animal signals ͉ habitat noise ͉ robotic lizard playbacks ͉ tropical lizard S ocial communication requires that signals be successively transmitted through the environment and detected by receivers. How animals minimize the effects of environmental degradation on signal propagation is a classic focus of communication research (1-3) and is often central to understanding the way animals communicate (4-6) and interact with each other (7-9). Signal detection theory (10) and empirical studies (3) show that simple signal components suffer lower rates of environmental attenuation than more complex, information-rich components. This results in a fundamental tradeoff in the evolution of signal design. A solution would be the production of a composite signal beginning with a simple conspicuous component (an "alert") that attracts the attention of a receiver, which is then followed by a more detailed "message" component

Is sociality required for the evolution of communicative complexity? Evidence weighed against alternative hypotheses in diverse taxonomic groups

“…This support can then be used to justify a more refined comparative analysis in which direct measures or more accurate data are collected by the comparative biologists themselves (e.g. see exploratory literature-based analysis of Ord & Martins [11] and subsequent follow-up field study by Ord et al [105]) or focused experimental research that confirms causal links between a putative selective force and its adaptive outcome [39,106].…”

“…On the one hand, the constraints acting on signal efficiency in microhabitats near noise sources or physical obstructions limit the range of signal designs that can be detected by receivers. On the other hand, animals can minimize masking by adding alert or amplifier components to signals and, in the process, increase the complexity of their signals [39,41]. Whether environmental variables constrain or promote signal complexity is unclear (but see [35]).…”

“…The influence of the environment on the transmission of animal signals is well documented [27 -30]. Background acoustic or visual noise masks calls [31,32] and displays [33,34] and obstructions in the environment deflect and scatter sound waves [28] and obscure visual signals [35,36], as does the reduced visibility imposed by poor light [37][38][39]. The strategies animals adopt to enhance signal fidelity in noisy, cluttered or dim habitats are varied.…”

“…There are, however, some instances where noisy environments can facilitate signal complexity by promoting the evolution of alert components. These are new components added to signals to attract the attention of receivers, before the more information rich portion of the signal is delivered [39,41]. Here, poor signal environments promote the evolution of more complex signals (i.e.…”

Arguments for the Integration of the Non-Zero-Sum Logic of Complex Animal Communication with Information Theory

“…Social communication requires signals to be detected by receivers. Research on communication has been so far focused on how animals are able to minimize the effects of environmental degradation on signal propagation [12], which is often crucial to the understanding of the way animals communicate and interact with each other (e.g., [13,14,15]). However, communication on noisy environments has not been adequately approached using the principles of communication theory.…”