Long distance calls: negligible information loss of seabird social vocalisations over propagation down to the hearing threshold

Abstract

How well does the information contained in vocal signals travel through the environment? To assess the efficiency of information transfer in little auk (Alle alle, an Arctic seabird) calls over distance, we selected two of the social call types with the highest potential for individuality coding. Using available recordings of known individuals, we calculated the apparent source levels, with apparent maximum peak sound pressure level (ASPL) of 63 dB re 20 {micro}Pa at 1 m for both call types. Further, we created a sound propagation model using meteorological data collected in the vicinity of the little auk colony in Hornsund, Spitsbergen. Using this model, we simulated call propagation up to the putative hearing threshold of the species, calculated to equal ASPL of signals propagated to roughly one kilometre. Those propagated calls were then used in a permuted discriminant function analysis, support vector machine models, and linear models of Beechers information statistic, to investigate whether transmission loss will affect the retention of individual information of the signal. Calls could be correctly classified to individuals above chance level independently of the distance, down to and over the putative physiological hearing threshold. Interestingly, the information capacity of the signal did not decrease with propagation. While this study touches on signal properties purely and cannot provide evidence of the actual use by the animals, it shows that little auk signals can travel long distances with negligible information loss. For the animals, this could mean that they can recognize calls of the members of their social networks as far as those calls are actually audible, and support the hypothesis that vocalisations could facilitate long-distance communication in the species.