Signal brevity and compression in loud calls of the white-headed langur

Zipf's law of brevity and Menzerath's law are linguistic principles, predicting that coding length is minimized for optimal coding efficiency. We tested whether two linguistic laws apply to vocal communication of white-headed langurs inhabiting karst forests. Adult male white-headed langurs produce three loud call types in long-distance sequences. Frequent call types were shorter in duration, supporting Zipf's law of brevity. Patterns related to Menzerath's law were more nuanced. Inter-call intervals shortened in longer sequences, but only wahoo calls showed duration compression. Physiological constraints caused calls to shorten and intervals to lengthen later in sequences. Longer sequences contained proportionally more short snorts and fewer long roars and wahoos. Signal compression reflects a trade-off between energy cost and communication efficiency. Constant durations of snorts and roars may aid long-distance transmission and caller recognition. These findings provide evidence for signal brevity and compression under physiological limits, offering insights into vocal communication evolution in non-human primates.