Mini-breaths and vocal-fry-like laryngeal register alleviate respiratory constraints on tokay (Gekko gecko) mating vocalizations.

Geckos are among the few non-avian reptiles that use acoustic signals for territorial defence, mate attraction and distress signalling. Although previously considered inflexible, male tokay geckos exhibit vocal plasticity by switching to longer, louder call types in noisy environmental conditions. However, they seem to face respiratory constraints limiting longer duration calls. To test this hypothesis, we combined acoustic analysis with deep learning-based pose estimation to quantify respiratory dynamics during spontaneous advertisement calling. Calls were produced exclusively during expiration at a constant rate, supporting the hypothesis that respiratory constraints limit call duration. Tokays use two mechanisms to increase bi-note call duration. First, bi-notes contain an inspiratory 'mini-breath'-a feature previously associated only with songbirds. Second, bi-note duration is increased by adding terminal pulses, whose acoustic signatures suggest vocal fold oscillation in the air-efficient vocal fry register. These findings suggest that tokay advertisement calls function as honest signals of respiratory capacity. We also observed slow closure of the ear opening during vocalizations, indicating a mechanism for protecting the auditory system from self-generated loud sounds. Unlike the reflexive auditory attenuation mechanisms of birds and mammals, this response appears tightly coordinated with vocal-respiratory activity, representing an additional evolutionary innovation associated with tympanic hearing.