Female preference for fast-rate, high-pitched calls in Hermann's tortoises Testudo hermanni

The courtship and mounting behavior of promiscuous tortoises is based on a multiple signaling system that includes visual, olfactory, tactile, and acoustic signals. Vocalizations related to mounting seem to be particularly intriguing because tortoises vocalize mainly at this time. Vocalizations and courtship behavior might be costly for males, and if these costs increase differentially for different males, then the potential exists for vocalizations and displays to reveal male individual quality on which females could base their mate choice. In the present study, by using individuals breeding in seminatural enclosures, we experimentally investigated whether the mounting call of male Hermann's tortoises (Testudo hermanni) represents a relevant stimulus to both males and females. We also looked for potential preference toward different acoustic stimuli in order to determine which call features, if any, played a role in attracting potential partners or deterring rivals. Females were sensitive to call playback, whereas males apparently paid little attention to playback. In addition, females showed a significant preference toward high-pitched calls emitted at high rate. Also, females exhibited a strong tendency toward short-duration calls. Because call rate is related to hematocrit in Hermann's tortoise males, by responding to fast-rate calls females are also choosing high-quality partners as sires of their offspring. This is the first study in which an attractive function of tortoise vocalizations has been documented.